Contents - Plural Publishing

Contents - Plural Publishing
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Contents
Preface
ix
1. INTRODUCTION
1
Overall Scope
Introductory Acoustics
Numbers Large and Small
Sound Transmission and Velocity
Waveforms
Sine Waves and Harmonics
Short-Term and Long-Term Average Spectra
Spectrograms
Decibels
The Performer’s Voice
Summary
Further Reading
2. THE HUMAN VOICE
1
2
3
5
8
10
12
15
18
21
21
23
25
Introduction
Voice Production
Power Source in Voice Production
Sound Source in Voice Production
Sound Modifiers in Voice Production
Voice
Place
Manner
Acoustics of the Vocal Output
Power Source and Sound Source
The Sound Modifiers
Perturbation Theory
Formants in Singing
Developing and Maintaining a Healthy Professional Voice
Computers in Voice Training
Tips for Maintaining a Healthy Voice
Maintaining a Healthy Voice—Summary
Summary
Further Reading
v
25
26
26
29
33
34
36
38
38
38
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51
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60
63
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VOICE SCIENCE, ACOUSTICS, AND RECORDING
3. THE VOICE ON LOCATION
Introduction
Acoustics of Spaces
Introduction
Sound Source into a Space
Sound Modification by a Space
Sound Output from a Space
Modifying the Acoustics of a Space
Introduction
Acoustics of Surface Materials
Calculating Reverberation Time for a Room
Changing Surface Materials in a Space
Performing to Best Acoustic Advantage in a Space
Introduction
Acoustic, Visual, and Practical Considerations
Working the Space to Best Acoustic Advantage
Vocal Performance Considerations
Summary
Further Reading
4. AUDIO SYSTEM FUNDAMENTALS
Introduction
Microphones
Introduction
Microphone Directivity Patterns
Microphone Frequency Response
Other Important Microphone Considerations
Microphone Summary
Voice Recording Systems
Introduction
The Microphone Preamp Stage
Conditioning the Signal Further—Inserts and EQ
Interfacing with External Devices—The Auxiliary Section
Routing and Output
Hearing the Result—The Group Outputs and Master Section
Insert Effects
Aux Send Effects
The Recording Medium
Vocal Sound Reinforcement
Introduction
Small Venues
Medium Sized Venues
Large Venues/More Complex Sound Reinforcement Systems
Operational Guidelines
Summary
Further Reading
67
67
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68
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75
78
78
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80
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85
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86
86
88
91
91
93
93
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CONTENTS
5. PRACTICAL VOICE RECORDING AND REINFORCEMENT
Introduction
Single Vocal Sources
Introduction
Recording for Research
Studio Vocal Recording
Live Vocal Sound Reinforcement
Spoken Word
Recording on Location
Anechoic Recording
Multiple Vocal Sources
Introduction
Stereo Recording
Multiple Soloists
Ensemble Recording
Background Vocals in Popular Music
Summary
Further Reading
Appendix
Appendix
Appendix
Appendix
Index
1:
2:
3:
4:
Glossary
Power Source (Breathing) Flip Book
Sound Source (Vocal Fold Vibration) Flip Book
Sound Modifier (Oral Tract Area) Flip Book
vii
147
147
149
149
149
150
155
158
160
162
164
164
164
169
173
176
177
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179
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191
195
199
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CHAPTER 2
The Human Voice
as the child is told for example, to “pipe
down,” “stop making such a noise,” “stop
shouting as we cannot hear ourselves
think,” “only speak when spoken to,”
“be seen and not heard,” “make a noise
quietly,” or “stop singing” Depending
on the severity with which such instructions are given, a typical response might
be some degree of clamming up in terms
of vocal output. This is likely to be
accompanied by and in part due to
increased muscular stress, especially in
the neck and shoulder regions, which is
in itself a common habit associated with
21st century living that is fundamental
to poor vocal health. Coupled with the
psychological result of being told by
parents and peers that a loud vocal output executed in a free and efficient manner is not routinely acceptable in daily
life, the clamming up and stressed
response becomes normal vocal habit
for many.
Unpacking these and other aspects
of less efficient, unnatural, and clammed
up vocal output is a key step to healthy
voice production and being able to project the voice efficiently in a babylike
fashion. Some knowledge of the voice
INTRODUCTION
One of the first things that a newborn
baby does is to cry in a wonderfully loud,
natural, unimpeded, and open manner.
This most basic activity provides a
means of communicating with those
around to request essential needs for living and growing up. A baby is born with
the ability to make sounds using the
voice production instrument, and during
the early years of childhood, the sounds
produced develop into the language in
local use through listening, imitating, and
observation of the responses obtained.
The cry of a newborn baby is acoustically efficient, free, and very well projected. It can be heard at a considerable
distance and the instrument itself is
working in a highly efficient manner.
However, this natural formula for playing the vocal instrument is rarely left
unhindered and therefore does not last.
A child’s developing use of the vocal
instrument is conditioned by parental
and peer response, which so often serves
to inhibit efficient voice production and
dampen vocal performance confidence
25
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VOICE SCIENCE, ACOUSTICS, AND RECORDING
production process in terms of its
anatomy and physiology, as well as the
acoustics of both the voice production
process and rooms, can greatly enhance
progress in healthy voice development.
Singing and speech make use of the same
vocal instrument, and the underlying
anatomical, physiological, and acoustic
principles involved are common to both
activities.
This chapter provides an introduction to the anatomy and physiology of
the human vocal instrument and then
focuses on the resulting acoustic output.
The presentation concentrates only on
those aspects that are vital for a proper
and fully informed understanding of the
basics of human voice production in the
context of vocal health and efficiency, as
well as vocal production in different
acoustic environments and making a
successful voice recording. The singing
as well as the speaking voice is considered, and the chapter ends with a number of everyday tactics that can be
employed to maintain the voice in a
healthy state.
VOICE PRODUCTION
This section describes the main parts of
the human body that are involved in
voice production, whether speaking or
singing. In order to produce a sound with
any system, whether an acoustic musical
instrument, an environmental noise, the
call of an animal, or an electronically
synthesized sound, three essential features must exist:
■ power source
■ sound source
■ sound modifiers
Human voice production during speech
or singing is no exception, and therefore
it will be described here in terms of the
power source, sound source, and sound
modifiers. During sung notes, these correspond anatomically to the action of the
lungs, the vocal folds, and the vocal tract,
respectively. These are illustrated in
Figure 2–1, which also shows an equivalent mechanical model, indicating with
double-ended arrows those parts that
can be moved during speech or singing.
The relevant anatomical and physiological detail of the power source, sound
source, and sound modifiers are described below in terms of their function
during voice production, the acoustic
output, and useful tips for maintaining a
healthy voice.
Power Source in Voice
Production
The power source in a musical instrument might, for example, be the bow
moving across the string of a stringed
instrument; a finger plucking a string on
a stringed instrument; the lungs blowing
air into a woodwind or brass instrument; a finger striking the key of a piano
or harpsichord; the electrical power supply of an electronic instrument; the
blower of a pipe organ; or the stick or
beater striking a percussion instrument.
For the human voice, the power source
is the flow of air from the lungs via the
throat and mouth and/or nose during
exhalation. Indeed, it is the same power
source used when playing woodwind
and brass musical instruments.
Breathing is a natural function which
is automatic and basic to life itself. While
the airways are open and the lungs
maintain a higher air pressure than the
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THE HUMAN VOICE
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Figure 2–1. An overview of the human vocal instrument when the
vocal folds are vibrating during either singing or speech in terms of its
three main constituent parts: power source (lungs), sound source
(vocal fold vibration), and sound modifiers (vocal tract spaces). The
anatomical equivalent is shown on the right and an equivalent simple
mechanical model on the left.
atmospheric pressure outside the body,
air flow is sustained from the lungs to
the outside world via the mouth and/or
nose. When lung air pressure is lower
than the atmospheric pressure of the
local environment, air flow is sustained
to the lungs from the outside world. This
is the basic physics behind how we
breathe. We change the air pressure in
the lungs relative to atmospheric pressure when we breathe. On breathing in
when singing or speaking in a healthy
manner, air is drawn into the lungs
by enlarging the lung spaces through
muscular action, which is equivalent to
pulling the piston in Figure 2–1 downwards and the bellows outwards. This
produces a lung pressure that is lower
than external atmospheric pressure
(same quantity of air now occupying a
larger volume results in a reduction in
pressure), and air will flow into the
lungs (providing the upper airway is
open). When we breathe out, through
muscular action we contract the lungs
(equivalent to pushing the piston in Figure 2–1 upwards and/or the bellows
inwards), thus producing a lung pressure that is higher than external atmospheric pressure (same quantity of air
now occupying a smaller volume results
in an increase in pressure) and air flows
out from the lungs (providing the upper
airway is open).
The lungs themselves are such that if
they were removed from the body they
would shrink greatly in size. Each lung
can in this respect be considered, albeit
rather crudely, as being somewhat similar to a balloon. However, there is a
fundamental difference between a lung
and a balloon in terms of inflation and
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VOICE SCIENCE, ACOUSTICS, AND RECORDING
deflation. The lungs are supported externally within the rib cage and from below
by the diaphragm so that they can be
physically enlarged to suck air in. Breathing in and out is a result of lung expansion and contraction, which is achieved
by the actions of muscles as illustrated in
Figure 2–2. First, there is a group of muscles that can move the rib cage by
expanding it outwards or contracting
it inwards. The muscles that join with
and control the size of the rib cage during breathing are known as the intercostals. The inspiratory intercostals
expand the rib cage and are therefore
used when breathing in, and the expiratory intercostals contract the size of the
rib cage and hence can be used when
breathing out.
Second, there is the action of the diaphragm which is attached to the lungs.
The diaphragm is bowed upwards
below the lungs when it is relaxed, as
shown in Figure 2–2. When it is contracted, it becomes shorter and its shape
flatter, expanding the lungs by pulling
them downwards (like a piston in a
cylinder). In addition, the lower rib cage
is opened outwards (rather like a blacksmith’s bellows). The lower part of Figure 2–2 illustrates an ideal breathing
sequence for which there is a flip book
version in Appendix 2. The diaphragm
sits over the abdominal wall, and since
Figure 2–2. An overview of breathing during singing and speech
showing how the lungs can be expanded and contracted using the rib
cage and/or the diaphragm, alongside the power source part of the
equivalent mechanical model shown in Figure 2–1. The double-ended
arrows indicate movement which can increase and decrease the volume of the lungs, and the model indicates the piston- and bellows-like
nature of lung action during breathing. The lower part of the figure
shows an idealized breathing sequence for which a flip book version
can be found in Appendix 2.
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THE HUMAN VOICE
the volume of the abdomen itself and its
contents cannot be altered appreciably,
any diaphragm contraction serves to
push down on the abdomen, which
causes the abdominal wall to bulge
outwards and air to enter the lungs (if
the airway is open). The diaphragm
is relaxed following contraction, and
it returns to its rest position and air is
expelled from the lungs (if the airway is
open). Note that the lungs are not empty
when the diaphragm is at its rest position; they can be further compressed to
enable longer phrases to be spoken or
sung. Abdominal wall expansion and
contraction are readily observed externally in the region of the navel, and this
provides a useful indicator of diaphragmatic breathing.
In summary, during breathing the
following muscles can be used:
■ breathing in: the inspiratory
intercostals and/or the diaphragm
■ breathing out: the expiratory
intercostals and/or the abdominals
Notice that these are the muscles we can
use to breathe and stay alive. The upper
chest region can also become engaged in
the process of breathing, as observed for
example during rapid panting. However, healthy voice use requires that the
upper body (chest, shoulder, and neck
region) remains relaxed in order that the
neck and larynx are relaxed and under
no excessive strain. This precludes the
use of the upper chest region for breathing when engaged in healthy voice production, so the predominant muscles
used for breathing are the diaphragm,
intercostals, and abdominals. Many voice
teachers refer to the notion of support or
supported breathing, which provides a
practical form of instruction, something
29
that might be termed a psychological hook,
to focus the mind of the performer on
controlling (or supporting) the lungs
from below.
Sound Source in
Voice Production
The sound source during sung notes
results from the vibration of the vocal
folds in the larynx. In this book, the term
vocal folds is used to describe the vibrating elements in the larynx, because it
describes most appropriately the physical nature of the vibrating structures. In
medical circles, the vocal folds are more
usually referred to as the vocal cords,
which has its origins in what Manuel
Garcia saw when he looked down the
throat with his 45 degree mirror (probably seeing the light reflecting from the
upper edges of each vocal fold, which
would have appeared to be string- or
cordlike). The media and other sources
often use the term vocal chords, which is a
misnomer, although one quick-thinking
York student justified the use of this
term in his submitted work by arguing
that the observed shape of each vocal
fold from above was a chord of a circle!
When a sung note is produced and
the vocal folds vibrate, the resulting
sound is heard as having a pitch. Such
sounds are described as being voiced,
because they involve vocal fold vibration in the larynx or voice box. Not all of
the sounds used in spoken communication are voiced and produced as a result
of the vibrating vocal folds, however.
There are unvoiced or nonvoiced sounds in
speech that result from air being forced
past a narrow constriction in the mouth
or oral cavity, such as the final consonants in the words pass, stiff, and pitch.
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Finally, there is a third sound source
used in voice production which is a mixture of the voiced and voiceless source,
when the vocal folds vibrate and air is
forced past a constriction, and this sound
source is termed mixed. The final consonants in the words fez, pave, and badge
have a sound source that is mixed.
In summary then, there are three
sound sources used in speech and
singing as follows:
■ voiceless (involving air being forced
past a constriction in the vocal tract)
■ voiced (involving vocal fold vibration)
■ mixed (involving voiced and voiceless
sound sources)
In terms of vocal training, almost all
effort relating to the sound source is
devoted to voiced sounds and the vibrating vocal folds. This is particularly true
for singing training, since a basic requirement is to gain a much wider pitch range
than is used for normal speech.
A voiceless sound source involves
a narrow constriction somewhere in
the vocal tract, for example between the
upper teeth and lower lip during the
production of the final consonant in stiff.
If air flows sufficiently fast through the
constriction, it becomes turbulent and a
noiselike sound is produced. Such sounds
are known phonetically as fricatives. The
occurrence of a noiselike sound when air
flow is rapid enough can be confirmed
by forming a constriction between the
upper teeth and lower lip in preparation
for producing an f sound and adjusting
the air flow from slow to fast while listening to the acoustic result. Voiceless
sounds have no definite pitch associated
with them; you cannot sing notes on
them—try singing the final consonants
in pass, stiff, and pitch. The production of
a voiceless sound source is learned as
speech is acquired, and unless there is
some speech-related issue about inappropriate positioning of the constriction
within the vocal tract, which would be
dealt with by a speech and language
therapist, nothing additional is needed
for the professional voice user. The
remainder of this section therefore concentrates on the voiced sound source.
The voiced sound source results
from the vibration of the vocal folds in
the larynx. The larynx is situated in the
neck, and it can be located by moving
the side of an index finger gently up and
down the front of the neck to find the
prominence on the thyroid cartilage,
known as the Adam’s apple, which can be
observed in the illustration of the larynx
shown in Figure 2–3. The Adam’s apple
is usually more obvious and clearly visible for men than it is for women,
because the adult male larynx is approximately twice as large in its linear
dimensions. If the side of the index finger is placed in contact with the neck on
the prominence of the Adam’s apple
while swallowing, a vertical movement
of the whole larynx structure can be felt.
This demonstrates that the larynx is supported by muscles in the neck; it is not
held rigidly in position.
Vocal fold vibration for a voiced
sound source is initiated by bringing the
vocal folds closer together horizontally—a movement known as vocal fold
adduction. Voiced sounds are normally
produced when exhaling (breathing
out). As air is expelled past the gap
between the adducted folds (this gap is
known as the glottis), the velocity of air
flow must increase because the airway is
narrower. One physical consequence of
increasing the velocity of air flow due to
a constriction is that the push or pres-
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THE HUMAN VOICE
sure that it exerts on the sides of the tube
is reduced. This is known as the Bernoulli
effect. It should be noted that it is possible
to produce voiced sounds when inhaling
(breathing in). This is something that can
occur automatically when one is communicating in a high state of panic,
shock, or fright to allow communication
Figure 2–3. Illustration of the tilting mechanism of the larynx, which enables the
length of the vocal folds to be altered and
thereby the fundamental frequency of
their vibration and the perceived pitch. The
upper panel shows a side view to illustrate
how the thyroid cartilage hinges on the
cricoid cartilage (marked with the black
circle). The lower panel looks down on the
larynx, revealing the vocal folds, which are
stretched and relaxed as a direct result of
the tilting mechanism.
31
to take place continuously, even when
breathing in. Producing a voiced sound
source when inhaling is also part of some
vocal warm-up/cool-down exercises.
The Bernoulli effect is also the principle upon which aircraft fly. Aircraft
wings are shaped as shown in the upper
part of Figure 2–4. Air flowing across the
upper surface has further to travel due
to the upward curve in the wing profile,
and therefore less pressure is exerted
downward on the upper surface of the
wing compared to the pressure exerted
upward on the lower surface, resulting
in lift, as illustrated. The Bernoulli effect
as it relates to the closure of the vocal
folds can be demonstrated by blowing
across a sheet of paper held at the end
nearest the lips, as shown in the lower
part of Figure 2–4. The sheet will rise up
(note the similarity in shape between the
curved sheet and the upper surface of
the aircraft wing) due to the Bernoulli
effect.
Figure 2–4. Illustration of the Bernoulli
principle as it relates to how aircraft fly
based on the profile of their wings (upper),
and a demonstration of the Bernoulli principle by blowing across a sheet of paper
held as shown at the end nearest the lips
(lower).
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During vocal fold vibration, air
flows between the adducted vocal folds
through the narrowed glottis, where the
air velocity increases with the consequential decrease in pressure on the
sides of the tube (the vocal folds themselves), as described by the Bernoulli
effect. The reduction in pressure on the
vocal folds acts to move them towards
each other, in a manner somewhat analogous to the lift on an airplane wing.
The result of moving closer together is
that the glottis is narrowed even more,
the air flow velocity increases, the pressure exerted on the vocal folds (tube
walls) reduces, and the force pulling the
folds together increases. The vocal folds
therefore accelerate towards each other
as they get closer together, until finally
they meet at the midline with a “snap”
as the glottis closes.
From the closed position, the vocal
folds will open because they have closed
off the air flow from the lungs, where air
is under pressure. In addition, the folds
have a natural tendency to return to
their rest/starting position— each vocal
fold can be thought of as behaving like
an oscillating pendulum. Each vocal fold
will move like a pendulum past its rest,
or equilibrium, position, on to its fully
open configuration, and back towards
its equilibrium position. The Bernoulli
effect again comes into play and the cycle
repeats, resulting in sustained oscillation. As the vocal folds vibrate, their
lower edges will meet and part before
their upper edges, since the folds have
depth as well as width (see Figure 2–5),
and the Bernoulli effect acts on their
lower edges first, due to the direction of
air flow. A flip book version can be
found in Appendix 3.
In speech and singing, the pitch of
the voice is always changing. Even in
Figure 2–5. Illustration of the sequence
of vibration of the vocal folds viewed from
the front (a flip book version of this figure
is available in Appendix 3). Notice that
opening and closing start from the lower
margins and move upwards.
singing when one attempts to sing a
steady note, there will be small changes
in pitch. During speech, changes in voice
pitch are the “tune” of the language, or
intonation pattern. English uses intonation to signify, for example, whether or
not one is uttering a statement or a question as in the following: “That train is
late!” and “That train is late?” Singers
change the pitch to alter the note they
are singing, and to tune their voices
with other singers or any accompanying
musical instrument(s). In speech, pitch
tends to be thought of in terms of a
changing contour, whereas in singing,
pitch relates to discrete notes.
The pitch of the vibrating vocal folds
can be changed by altering their mass,
tension, and/or elasticity; this is described
by the myoelastic aerodynamic theory of
vocal fold vibration (see Van den Berg
[1958] in the further reading list for more
details). Increasing the mass, reducing
the tension, or making the elasticity
smaller will have the effect of lowering
the pitch, and vice versa. In practice, the
mass can be changed by holding a portion of each vocal fold immobile, which
means that their vibrating masses are
reduced and the pitch will rise. The vocal
folds are supported within the larynx
within a hinged structure, as illustrated
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THE HUMAN VOICE
in Figure 2–3, in such a way that the
folds can be stretched and released, raising and lowering their f0, respectively.
Sound Modifiers in
Voice Production
The acoustic characteristics of a sound
will be modified by the spaces through
which it passes in much the same way as
the sound of the voice varies in different
rooms and buildings. In the case of
speech and singing, the sound modifiers
are the spaces through which the sound
source passes to emerge from the between
the lips and/or nostrils of the speaker or
singer. It is the shape of these spaces that
serves to modify acoustically the output
from the sound source. There are two
spaces that make up the vocal tract:
■ the oral cavity (the space between
the glottis and the lips)
33
■ the nasal cavity (the space between
the velum and the nostrils, or the
nose)
The main way in which the shape of the
oral cavity (mouth and pharynx in Figure 2–6) can be altered is by moving the
tongue, jaw, and lips. Such moving parts
are known as the articulators, and those
that can be moved when speaking or
singing are illustrated in Figure 2–6
with double-ended arrows on the equivalent mechanical model of the sound
modifiers.
The main articulators serve to alter
the shape of the mouth, and the main
ways in which this can be achieved in
speech and singing are by varying the
height of the jaw, the position of the lips
between being rounded (as in the vowel
in boo) and spread (as in the vowel in
bee), and/or by changing the shape of
the tongue by increasing the constriction
between it and the hard palate using its
Figure 2–6. The human vocal tract showing the main parts associated
with voice production (left) alongside the sound source and sound
modifier equivalent mechanical model (right), shown in Figure 2–1. The
parts that can be moved are indicated by double-ended arrows on
the mechanical model and their names can be found by referring to the
vocal tract (left).
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VOICE SCIENCE, ACOUSTICS, AND RECORDING
tip, blade, front, or back. The nose is
rather different because its shape cannot
be altered. It is used in voice production
for sounds such as the final consonants
in boom, bean, and bring, the so called
nasal consonants in English. The nose is
engaged by changing the position of the
soft palate or velum, which works as a
valve to allow sound to pass through the
nose or not, depending on whether it is
lowered or raised, respectively (see the
mechanical model in Figure 2–6). It is
possible to feel the action of the velum
if a hum is produced that is broken up
by forming but not releasing a b (the
first consonant in boo); one might write
this as mmmbmmmbmmmb. “Not releasing a b” sound means not opening the
lips—let it revert to the hum. It should
be possible to feel the action of the
velum as it is raised when the b is
formed (to shut the nose off from the
airstream), and lowered for the hum (to
allow air to flow through the nose and
out via the nostrils).
The minimum set of sounds required
to distinguish the words of a language
are those that are uniquely in the words
of that language. For example, the English words ton, done, shun, son, gun, run,
won, nun, fun indicate that the initial consonant sounds are unique phonemes for
English, since exchanging them in this
context produces different meaningful
words. Similarly, the vowel sounds that
distinguish the words bat, bit, but, bet,
boat, bait, bite, bought, beat, boot, Bert, and
Bart are also phonemes of English. It
turns out that English has 24 consonants
and 20 vowels (a total of 44 phonemes)
when its unique sounds are considered,
which is very different from the 5 vowels
and 21 consonants (a total of 26 letters)
that exist in the alphabet used when
writing words; the correspondence
between the phonemes used to indicate
how a word is spoken and how the word
is spelt is rarely one-to-one.
The articulation of the phonemes
in English would be described by phoneticians in terms of three descriptors:
voice, place, and manner, which indicate
whether the vocal folds vibrate or not
(voice), where (place), and how (manner)
the sound is produced. Table 2–1 lists
the 44 phonemes of English using the
SAMPA (Speech Assessment Methodologies Phonetic Alphabet) transcription
system introduced by John Wells in
1989. The SAMPA system is used here
because it makes use only of characters
that are available on a standard computer keyboard using ordinary fonts.
For each phoneme, an example word
(from the world of yachting) is provided
along with its SAMPA transcription, and
for the consonants, their voice, place,
and manner labels are provided, which
are described in the next sections.
Voice
The voice label indicates whether or not
the vocal folds vibrate during the production of the phoneme, which is described
as being either voiced (V+) because the
vocal folds vibrate or voiceless (V−)
because they do not. A quick check to
confirm whether the vocal folds vibrate
while producing a sound can be made
by either (a) putting hands over the ears
and listening for a loud buzzing sound,
(b) trying to sing the sound, or (c) feeling
either side of the throat gently near the
level of the Adam’s apple for vibration.
A number of English phonemes differ
only by voice including the initial consonants in Sue and zoo, fire and via, chew and
Jew, pan and ban, ton and done, as well as
p
b
t
d
k
g
T
D
f
v
s
z
S
Z
h
tS
dZ
m
n
N
w
r
l
j
rope
buoy
tide
deck
cabin
galley
thwart
weather
fog
rung
sea
zenith
ship
treasure
heeling
chain
jibe
mast
main
rigging
winch
rain
lee
yacht
Word
/[email protected]/
/bOI/
/taId/
/dEk/
/k{bIn/
/g{li/
/TwOt/
/[email protected]/
/fQg/
/rVN/
/si/
/zEnIT/
/Sip/
/[email protected]/
/hilIN/
/tSeIn/
/dZaIb/
/mAst/
/meIn/
/rIgIN/
/wIntS/
/rein/
/li/
/jQt/
Trans.
V−
V+
V−
V+
V−
V+
V−
V+
V−
V+
V−
V+
V−
V+
V−
V−
V+
V+
V+
V+
V+
V+
V+
V+
Voice
bilabial
bilabial
alveolar
alveolar
velar
velar
dental
dental
labio-dental
labio-dental
alveolar
alveolar
palato-alveolar
palato-alveolar
glottal
palato-alveolar
palato-alveolar
bilabial
alveolar
velar
bilabial
alveolar
alveolar
palatal
Place
plosive
plosive
plosive
plosive
plosive
plosive
fricative
fricative
fricative
fricative
fricative
fricative
fricative
fricative
fricative
affricate
affricate
nasal
nasal
nasal
semivowel
semivowel
semivowel
semivowel
Manner
i
I
E
{
A
Q
O
U
u
V
3
@
eI
aI
OI
@U
aU
[email protected]
[email protected]
[email protected]
Sym.
neap
jib
red
anchor
hard
locker
port
foot
food
rudder
stern
tiller
weigh
light
oilskin
row
bow
pier
fare
fuel
Word
/nip/
/dZIb/
/rEd/
/{[email protected]/
/hAd/
/[email protected]/
/pOt/
/fUt/
/fud/
/[email protected]/
/st3n/
/[email protected]/
/weI/
/laIt/
/OIlskIn/
/[email protected]/
/baU/
/[email protected]/
/[email protected]/
/[email protected]/
Trans.
ENGLISH VOWELS
10/7/07
Sym.
ENGLISH CONSONANTS
Table 2–1. The 24 consonants and 20 vowel sounds in English with their SAMPA symbols (Sym.), example
words (Word), and SAMPA (see Wells, 1989, in the reading list) transcription (Trans.). The voice, place, and
manner descriptions are listed for the consonants
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VOICE SCIENCE, ACOUSTICS, AND RECORDING
cot and got. In each of these examples,
the first of the pair is voiceless and the
second is voiced. Table 2–1 shows the
voice label for each English consonant.
Place
The place of articulation describes where
in the vocal tract there is either a complete closure or vocal tract narrowing.
The main places of articulation used
for English consonants are shown in
Figure 2–7 and are listed in Table 2–1.
The bilabial sounds /p/, /b/, and /m/
involve contact between the lips. The
labio-dental sounds /f/ and /v/ result
from contact between the lower lip and
the upper teeth. Dental articulation is
used for the sounds /T/ and /D/, which
use contact between the tongue tip and
the upper teeth. The alveolar sounds
are /t/, /d/, /n/, /l/, /s/, and /z/, for
which the tongue tip or blade makes
Figure 2–7. The places of articulation used
for English consonants.
contact with the alveolar ridge. The /r/
sound is post-alveolar because it is usually produced with tongue contact further back along the hard palate than for
the alveolar sounds. There is close
approximation between the front of the
tongue and the area between the alveolar ridge and hard palate for /S/, /Z/,
/tS/, /dZ/, and /j/, which are therefore
known as palato-alveolar. For /k/, /g/,
and /N/, the back of the tongue makes
contact with the soft palate or velum
and their place is described as velar. The
sound /h/ is produced with a close
approximation of the vocal folds, and its
place is known as glottal (the space
between the vocal folds is the glottis).
The vowel sounds in British English
include both those that remain steady
throughout (/i/, /I/, /E/, /{/, /A/, /Q/,
/O/, /U/, /u/, /V/, /3/, and /@/),
which are known as monophthongs, and
those that change from one vowel to
another during their production (/eI/,
/aI/, /OI/, /@U/, /aU/, /[email protected]/, /[email protected]/, and
/[email protected]/), which are known as diphthongs.
The production of monophthongs is described in terms of four elements: (a) how
close or open the constriction is between
the closest part of the tongue to the roof
of the mouth, (b) whether it is the front,
center, or back of the tongue which is
making that constriction, (c) whether
the lips are rounded or unrounded, and
(d) whether the vowel is nasalized.
Traditionally, vowels are shown on
a vowel quadrilateral, which shows the
position of each vowel by indicating
the position of the highest point of the
tongue. The vowel quadrilateral for
the English monophthongs is shown in
Figure 2–8, along with an indication of
the position of the quadrilateral itself in
relation to tongue position in the mouth.
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37
Figure 2–8. The approximate position of the vowel quadrilateral within
the vocal tract (upper left) with vowel quadrilateral plots of English
monophthongs (upper right), closing diphthongs (lower left), and centering diphthongs (lower right) plotted on vowel quadrilaterals. SAMPA
(Wells, 1989) symbols are used throughout.
The vertical and horizontal axes are
open/close and front/back, respectively.
Lip rounding can be externally observed.
The full description for the vowel /i/ is
front, close, and unrounded, while /u/
is back, close, and rounded, and /{/ is
front, open, and unrounded.
Any vowel can become nasalized
when the velum is lowered and the
nasal cavity is coupled to the oral cavity.
This happens when there is a nasal consonant either before or after the vowel,
and the velum is either still lowered after
the nasal consonant, or lowered in preparation for the nasal consonant. A nasalized vowel is sometimes described as
sounding hollow when compared to its
non-nasalized counterpart.
Diphthongs are vowels which do not
remain steady; rather, there is a change
from one monophthong to another. This
can be readily appreciated in Figure 2–8
where the traditional representation of
each diphthong is shown as an arrow
from the first to second monophthong,
which provides a representation of the
associated movement of the highest part
of the tongue during their production.
For example, the diphthong /aI/ (eye)
involves a glide between the monophthongs /a/ and /I/, and the diphthong
/[email protected]/ (ear) glides between /I/ and /@/.
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been specifically acoustically designed
as performance spaces. In many cases,
humans are using their voices on a daily
basis in rooms that have been constructed
with no consideration having been given
to acoustic design, such as many school
classrooms, seminar rooms, lecture halls,
hotel ballrooms, club back rooms, and
church halls. Intelligibility depends on
the relative levels of the direct sound
and the reverberant field; this and the
importance of the critical distance have
been introduced in the section Sound
Modification by a Space. In terms of a
vocal performer, there are two key
aspects to consider: (a) how well the performer can monitor her/his own voice,
and (b) how comfortably and intelligibly
the audience can hear the sound. There
are a number of things that can typically
be used to improve both these situations
in practice, and practical suggestions
supported with underlying reasoning
are provided below.
PERFORMING TO BEST
ACOUSTIC ADVANTAGE
IN A SPACE
Introduction
Any performance requires preparation,
and since the acoustics of the performance space affect the sound received by
the listeners, attention should be paid to
achieving the best acoustic result from
the space itself. Some time needs to be
devoted to this prior to any performance
in order to gain familiarity with the
acoustics of the space itself, and to consider making changes to its layout. No
special equipment is needed but the
results can be dramatic in terms of the
85
overall performance as seen and heard
by the audience. The acoustics of the
space should be viewed as a tool that is
available to the vocal performer. While
proper attention to making the space
work well acoustically can enhance the
final result, using it as offered having
gained no familiarity with it in advance
can trip up even the best vocal practitioners to the detriment of the final result.
Bearing in mind that the acoustics of
a space are determined by the relative
positions of the sound source and the
listener, it is worth thinking creatively
about how a room is laid out for a performance. Even if there is a stage, it is
not necessarily the case that that stage
is the acoustically optimal place from
which to perform. If the audience seating is not fixed, the possibility of moving
the seating around should be considered. This is especially important when
working in spaces that have not been
designed acoustically for optimum vocal
performance such as most church halls,
school classrooms, seminar rooms, conference breakout rooms, hotel ballrooms,
and other spaces where the seating is
moveable. When considering where to
perform from within a space, however,
there are clearly also visual and practical
issues to resolve when considering changing the sound source and/or listener
position for best acoustic effect.
Different types of music work better
acoustically in different spaces, and
choral conductors should be aware of
this when planning programs to be performed in different venues. Music with
much rapid contrapuntal detail will tend
to become blurred and the detail lost in
a building with a high reverberation time,
whereas slow-moving polyphonic music
works can be significantly enhanced
when performed in spaces with high
reverberation times, such as a cathedral.
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VOICE SCIENCE, ACOUSTICS, AND RECORDING
Acoustic, Visual, and
Practical Considerations
Acoustically it is important (see section
on Sound Modification by a Space) that
(a) the balance between the direct sound
and the reverberant field is optimized
for intelligibility, pleasantness, and overall loudness, and (b) the performer is
able to monitor the output comfortably
to combat any tendency towards vocal
strain. It is better acoustically to have
the audience close to the performers to
allow a maximum number to be within
the critical distance, thereby providing
them with a high direct sound level. If
those in the audience who are further
away are having difficulty hearing a
vocalist, then the acoustic level can be
raised by increasing the reverberant
field level. This requires an increase in
reflected sound, which might be achieved
by opening curtains to acoustically
expose window glass, or by removing
acoustically absorbing surfaces or objects.
Conversely, if the sound is too reverberant, which will tend to impair intelligibility particularly for those at the greatest distance from the performers, the
reverberant field level can be reduced by
closing curtains and/or adding acoustically absorbing surfaces or objects. Such
modifications have to be done judiciously, however, to achieve a balance
between overall level and intelligibility,
noting that this can never be optimal for
every member of the audience.
Visually it is important that the performers can be seen clearly by the audience and that the number of blind spots
(such as seats with obscured views due
to pillars, other members of the audience
sitting further forward, or other obstructions) is minimized. It is also essential
that the performers can see the audience
easily to gain and maintain eye contact,
to enable their reaction to be gauged
during the performance, and to make
appropriate changes as the performance
progresses. There may, of course, be issues
relating to the lighting to be resolved to
ensure that visual contact is two-way. If
there are blind spots, it can be useful if
the performer moves around whenever
possible to help resolve them, but it
is worth being aware that movement is
likely to create new blind spots elsewhere. A constant awareness of one’s
audience gained by looking around will
keep track of and allow something to be
done about full audience inclusion. Bear
in mind that a blind spot blocking the
view for a member of the audience is also
a blind spot preventing the performer
from seeing that member of the audience.
Practically, there can be a large
acoustic difference in performing from
different positions. In many situations it
is not feasible to move the audience; perhaps the seating is fixed, there is a stage,
podium, or lectern, or regulations state
that the fire exit doors have to be at the
back, front, or side. However, as a performer there is always the possibility of
making an informed decision as to the
performance position. The presence of
a lectern or podium does not necessarily
indicate the optimal position from
where to perform; its position has more
likely been decided based on overall
visual appearance.
Working the Space to Best
Acoustic Advantage
Finding a good acoustic position from
which to perform can be done by testing
the acoustics of the space by moving
around it using a handclap as a sound
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source and listening to the result. A handclap is a single, short acoustic sound
input to the space, and the sound modifying effect of any space will present the
direct sound, early sound, and reverberant sound (see Figure 3–4) to any ear or
microphone within the space. One thing
to listen out for is flutter echoes, which
are best described as a ping—a ringing
note. If flutter echoes are present, it
means that any sound produced by a
sound source placed in the position
where the handclap was made will be
colored by that ping. Flutter echoes
occur when the sound source is between
two exactly parallel and smooth surfaces, and the resulting sound modification effect is to produce a ping as the
sound is trapped between the parallel
surfaces, being reflected back and forth.
Flutter echoes should be avoided if at all
possible; continue moving around the
space testing with handclaps to find a
spot without them (they are usually
localized over quite a small region of
sound source positions).
When performing on a stage, it is
important to be aware that the stage
is acoustically like a small room linked
to a larger room (the auditorium). This
is particularly the case when there is a
proscenium arch at the join and the
sound energy levels arriving in the auditorium can be considerably lower than
those in the stage area. Once again the
best advice is to listen to the space and
get to know its sound. Ask a colleague to
stand and speak or sing from the performer’s position on stage and move
around both the stage and the auditorium to obtain a listener’s ear view of
the sound output from the space in different positions as well as a comparison
between the sound energy levels onand off-stage.
87
In some situations, background noise
can be a serious issue. This is less likely
in a space designed for public performances, such as theaters, lecture halls,
and opera houses, but relatively high
levels of noise are sometimes present in
other spaces where one is asked to perform vocally, such as classrooms, church
halls, or back rooms in pubs, clubs, or
hotels. These are the unwanted sound
sources as illustrated in Figure 3–2, and
they can either be internal or external.
Noise can obscure or mask other sounds,
and in the context of speech or singing,
certain sounds of the language can be
lost to the listener depending on the
nature of the noise, thereby compromising intelligibility.
The sounds that are affected by noise
will depend on the nature of the noise
itself. Noise that is hisslike contains high
frequency components and it will tend
to mask sounds with high frequency
components (see Chapter 2) such as
fricatives. Buzzlike noises, such as the
drone of electric motors in ventilation or
air conditioning systems, will tend to
mask frequency components in the formant frequency range, potentially masking vowels. Traffic or aircraft noise tends
to cover a wide frequency range and
therefore has the potential to mask all
sounds. Short bursts of noise, perhaps
from hammering, can affect the perception of plosive bursts.
One way to combat noise is to speak
or sing at a higher level, but this is not an
ideal solution as it places undue strain
on the performer’s voice. It is worth listening to a space to appreciate the nature
of the unwanted noise—it is rare to find
a space with no unwanted noise! Sometimes the source of the noise can be
turned off. Perhaps a heater or ventilation fan could be turned off at the start
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VOICE SCIENCE, ACOUSTICS, AND RECORDING
of the session, turned on again in the
interval, and off again for the second
half. If the noise is external, perhaps
from traffic or aircraft, then it is worth
ensuring that windows are closed properly, noting that if they are required to
be open for ventilation, they could be
closed at the start of the session, opened
in the interval, and closed again for the
second half.
The sources of some noises may not
be identifiable or may not be locally controllable. Usually a noise will be worse
in some parts of the space, and if this can
be identified by careful listening, there
may be scope for changing the layout of
the room to avoid any noise hot spots.
One other form of noise that cannot be
checked beforehand is that produced by
the audience. Have a strategy thought
out for dealing with audience noise such
as chatter, mobile telephones, or late
arrivals. Raising the performance level
to combat such noises rarely works since
the noise levels will often be raised also,
and this does have an acoustic energy
cost that could result in vocal problems
if it becomes a persistent habit. One
method that can work very well is
silence—a silent pause accompanied
with a stare towards the noise source can
be most effective and it has no acoustic
energy cost!
Vocal Performance
Considerations
A key element of vocal performance,
whether singing or speaking, is communication of the text. The acoustic effect
of the space can serve to destroy all
endeavors to annunciate consonants
carefully, because the overall sound
reaching the ears of listeners who are well
beyond the critical distance (see Sound
Modification by a Space) is “blurred” or
“mushy,” so that the acoustic detail that
is important for distinguishing between
individual sounds is lost, with the result
that the message becomes very difficult
to understand.
Figure 3–8 illustrates this effect in
terms of how reverberation serves to
extend individual sounds acoustically in
time, and the potential there is for them
to overlap. The figure shows the average
pressure level of the two consonants in
the word beat (SAMPA: /bit/), for the
situations where /b/ is louder than /t/
and /t/ is louder than /b/. The reverberation decay is indicated for a short
and a long reverberation time (RT60); this
is how the energy of each consonant
would decay. Notice that the later consonant is the one that could be obscured or
masked by the reverberant decay of the
first, and that this is the case for the long
RT60 shown. When the later consonant
/t/ is louder than the first /b/, complete
masking cannot occur. Deliberate articulation of final consonants is therefore
particularly important in highly reverberant spaces to combat this effect and
ensure that the listener is provided with
the acoustic cues required to enable all
sounds to be heard clearly and identified. In addition, shortening individual
syllables or sounds and lengthening the
gaps between them will make space to
allow the reverberation to die away
before the next acoustic event.
One of the less well understood and
compensated for acoustic issues facing
anyone using his voice regularly in front
of a group of people is the extent to
which he can hear himself adequately.
This is vitally important, because our
vocal output is continuously being monitored by our brain, known as self-
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89
Figure 3–8. Illustration of the potential masking effect of a short
and a long reverberation time (RT60 ) on the second consonant /t/
in beat (SAMPA: /bit/) by the first consonant /b/, depending on
their relative levels.
monitoring. If the acoustic energy level
reaching our ears is insufficient, the
brain insists that we speak louder so that
it can carry out its monitoring job effectively. This is what triggers a tendency to
speak or sing louder than is comfortable
(and often louder than is actually necessary as far as the audience is concerned),
and therein is a common route to vocal
strain or more serious vocal problems.
This is particularly an issue for those
such as teachers or lecturers who use
their voices over long periods. Teachers
are the largest group presenting for
medical attention relating to vocal issues
such as strain, laryngitis, or hoarseness.
So often, the cause is simply an inability
to self-monitor adequately.
Increasing the level of the direct
sound that is fed back to the ears of the
performer can help to sort this issue out,
and this can be achieved in a relatively
straightforward manner. Starting with
an awareness of the issue, creative possibilities can be thought through to
improve matters through the use of
acoustically reflecting surfaces placed
close to the performer to provide foldback. Such reflectors are usually placed
behind the performer, so that they are
not only of benefit to the performer, but
they also enhance the overall sound
level that reaches the audience.
Specially made reflectors do exist,
but there are ways of moving towards
improving foldback using existing materials or apparatus. Any hard surface,
such as a white board or blackboard, will
serve as an acoustic reflector to provide
foldback, and often these are on wheels
and can be readily moved. Acoustic
screens are becoming increasingly available for use in orchestras and music
groups to shield the ears of players
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sitting in front of loud instruments (e.g.,
percussion and brass) following renewed
concerns about overall sound levels in
public spaces. In some areas (in the
United Kingdom this last occurred in
April 2006), the maximum levels allowed
have been lowered, prompting the provision of acoustic screens on health and
safety grounds. Where such screens,
which are usually made of thick acrylic
and mounted on wheels, are available,
try them out as reflectors to enhance
what the performer is hearing.
When a reflector is set up to provide
foldback to the performer, it is important
to ensure that the delay involved is not
too great. Delay will be incurred because
the path travelled by the acoustic wave
from the performer to the reflector and
back to the performer’s ears takes time,
which can be determined from the velocity of sound (usually taken as 344 meters
per second— see Chapter 1). A delay of
no more than about 25 ms will typically
not interfere with the benefits provided
by the foldback, and in that time sound
can travel 8.6 m. (The velocity of sound
is 344 meters per second, so in 25 ms [or
0.25 s], sound will travel a distance equal
to the time multiplied by the velocity,
which is 344 × 0.25 = 8.6 m.) Remembering that the sound has to get to the
reflector and back, this means that a
foldback reflector should be placed
within 4.3 m (half of 8.6 m) of the performer. In a small room, there is likely to
be at least one wall within 4.3 m of the
performer that will serve to provide
foldback. However, in a large hall there
probably will not be a surface that is
close enough to act as a foldback reflector, and that is when it is worth setting
up a local reflector.
When working on stage with scenery,
it is worth being aware of the potential
benefit of improving foldback, especially when performing a major speech,
song, or aria. If a speaker is suffering
unanticipated vocal strain or a singer is
experiencing unexpected tuning difficulties, this could be due to a lack of
an appropriate foldback level. With the
director’s agreement (or instruction),
they could perhaps be positioned within
4.3 m of a piece of scenery that could
provide acoustic foldback, or perhaps the
scenery could be appropriately added to
or rearranged.
The importance of foldback has been
known to professional pop groups for a
long time. Vocal performers are provided
with local loudspeakers to provide an
appropriate mix of the overall sound
output as foldback, which includes their
own vocal output. These loudspeakers
are usually placed on the stage, so as not
to be visually intrusive, with their loudspeakers facing upwards at 45 degrees
towards the ears of the performer to
localize the sound. Due to the shape of
the loudspeaker cases, they are often
referred to as wedges. Alternatively, foldback can be provided directly into the
ears of vocal performers via bud earphones. This is known as in ear monitoring
and it is especially useful for performers
who move around a lot. For vocalists, it
is vital that the foldback balance of relative levels of the different instruments
and their own vocal output is appropriate. Good working relationships between
whoever is in charge, the sound team,
and the vocalists are an important part
of vocal care in such situations.
When performing with acoustic
instrument accompaniment, it is important to ensure that the accompaniment
can be heard comfortably to maintain
intonation and a proper balance for both
performers and audience. It is always
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worth moving around to find the best
position acoustically, and then to consider
how that position might be modified to
provide best visual presentation to the
audience. Often, just a small repositioning can make a huge difference to the
overall acoustic coherence of a performance while also serving to provide less
chance of problems for vocalists.
SUMMARY
This chapter has introduced sound transmission in a space from the sound source
to the microphone or ear of the listener.
The concepts of direct sound, early
sound, and reverberant sound enable the
nature of the sound output from a space
to be better understood in terms of how
this output sound changes for different
sound source or listener positions in
a space, and the possibilities that exist
for practical and inexpensive acoustic
modifications that might be made to a
space.
When performing as a vocalist in a
space, it is essential to remember that the
acoustics of the space itself are a part of
the performance. The acoustics of the
space should be used to best advantage.
Performance spaces are often well set up
acoustically, and often there is little
choice as to the performance position.
Everyday work spaces are rarely set up
acoustically, and there are a number of
things that can be considered that can
make it easier both for listeners to comprehend the message and for the performer’s voice. Any use of the voice in
any job is a performance. Considering it
as such while taking advantage of the
advice given herein has the potential not
only to improve the quality of vocal life,
91
but also to gain esteem from those observing the performance. You only have one
voice; look after it and use it well.
FURTHER READING
Acoustics of Spaces
Beranek, L. L. (1954). Acoustics. New York:
McGraw-Hill.
Howard, D. M., & Angus, J. A. S. (2001).
Room acoustics: How they affect vocal
production and perception. In P. H.
Dejonckere (Ed.), Occupational voice—Care
and cure (pp. 29–46). The Hague, Netherlands: Kugler.
Howard, D. M., & Angus, J. A. S. (2006).
Acoustics and psychoacoustics (3rd ed.).
Oxford, UK: Focal Press.
Modifying the Acoustics
of a Space
Everest, F. A. (1984). The master handbook of
acoustics. TAB Books.
Everest, F. A. (1989). Acoustic techniques for
home and studio (2nd ed.). TAB Books.
Howard, D. M., & Angus, J. A. S. (2006).
Acoustics and psychoacoustics (3rd ed.)
Oxford, UK: Focal Press.
Performing to Best Advantage
in a Space
Howard, D. M., & Angus, J. A. S. (2001).
Room acoustics: How they affect vocal
production and perception. In P. H.
Dejonckere (Ed.), Occupational voice—Care
and cure (pp. 29–46). The Hague, Netherlands: Kugler.
Potter, J. (2001). The Cambridge companion to
singing. Cambridge, UK: Cambridge University Press.
Smith, B., & Sataloff, R. T. (2000). Choral
pedagogy. San Diego, CA: Singular.
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been working hard for some time. Computer hard drives can also be sources of
noise. In such a situation it is very worthwhile to try to source quiet equipment
that will not cause such problems. Noncomputer based stand-alone recorders
or flash memory devices that have no
mechanical parts might be good compromises. Alternatively, arrange additional absorbing material around the
noisy equipment and place it carefully
away from the vocal source in a corner
of the chamber if possible. The other
consideration with bringing in additional equipment is that it may be a possible cause of acoustic reflections (e.g., a
laptop screen), and so careful positioning and the use of additional absorbing
material should be considered.
The second problem to consider is
the nature of the environment itself and
its impact on the vocal performer. Listening to one’s own voice in a completely
reflection-free environment is a very
unusual experience and can become tiring after prolonged exposure. Regular
rest breaks in the session might be
required, or alternatively, the performer
should have a good headphone foldback
mix with some additional reverberation
added. If the latter approach is used,
care should be taken to keep levels low
to avoid headphone sound leaking into
the microphone.
MULTIPLE VOCAL SOURCES
ronment, this section is concerned with
capturing the entire acoustic event— the
sound of the voice source in the acoustic
space within which it has been placed.
Generally, this implies that there is no
longer a solo performer but rather a
number of vocalists that make up the
specific sonic event. These vocalists may
be spatially distinct and therefore considered as separate solo sources or, more
commonly, be grouped together in an
ensemble such as a choir. Stereo microphone techniques are also introduced
as these methods are generally more
appropriate for capturing the complete
source plus environment combination
rather than just the individual source.
The one exception to this that was not
included in the previous section is soloist
recording in a performance venue without sound reinforcement. In this scenario,
the desire is again to capture the sound of
the complete event rather than the individual, and a stereo recording is the most
appropriate solution. Hence, this special
case is covered as part of what follows.
Stereo Recording
Under normal listening conditions we
use our two ears, separated by our head,
to locate the direction from which a
sound source is originating. We rely on
a number of auditory mechanisms to
help us determine this source direction
and they are summarized as follows.
Interaural Time Difference (ITD)
Introduction
Whereas the entire purpose of the previous section was to use microphone and
recording techniques to remove the solo
vocal source from the surrounding envi-
Depending on direction, the sound
source will arrive at one ear before the
other, resulting in a very small amount
of difference in arrival time between left
and right ears. This only works for low
frequencies.
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Interaural Level Difference (ILD)
Depending on direction, the sound source
will be louder in the ear that is oriented
more closely to the source, resulting in
level difference between left and right ears
of up to 20 dB SPL at some frequencies.
This does not work at low frequencies,
as the sound wave will diffract around
the head such that the level difference
between the two ears is negligible.
Pinnae Cues
ITD and ILD only give enough information to locate a source in two dimensions. The actual shape of the outer ear
imparts a direction dependent frequency
characteristic on the incident sound that
helps to resolve front-back and up-down
differences.
Head Movement
When attempting to work out the direction of a sound source, very slight head
movements act to constantly change the
relative ITD, ILD, and pinnae cues so that
a listener can more easily and quickly
determine source location. Primarily this
acts to minimize ITD and ILD values to
a point that they are essentially zero.
This implies that the sound source is
either directly in front of or behind the
listener, and pinnae cues—and of course
sight—can help to determine the final
source direction.
With knowledge of these directional
properties of the ear, particularly those
relating to ITD and ILD, it is possible to
fool the ear into perceiving a directional
effect through just a pair of speakers or
headphones—what we typically refer to
as stereophonic or stereo audio presentation.
There are two main ways of recording
stereo sound images for presentation over
a pair of loudspeakers—coincident stereo
and spaced stereo microphone techniques.
165
Coincident Stereo Microphone
Recording
This technique uses a pair of identical
directional (not omnidirectional) microphones, each connected to a separate
audio channel. To create robust, stable
sound images suitable for stereo presentation, it is considered important to minimize time differences between left and
right channels, and so the two microphones must be placed as close together
as is physically possible — hence the
term coincident stereo (also known as,
XY, crossed pair, or normal stereo). The
result is that sound sources are captured
with differing levels between the two
channels. This is due to the directional
characteristics of the microphones used
and the fact that signal amplitudes will
vary in direct relation to the physical
angle between the microphone pair and
the sound source. Hence, this technique
works well at presenting realistic and
natural stereo sound because it is based
on how the ILD works with the auditory
system. The normal method is to place
the capsule of one microphone immediately above the other, so that they are
coincident in the horizontal plane, which
is the dimension from which sound
image positions will be created.
Coincident stereo is actually based
on simple amplitude panning, as implemented in the mixing desk channel pan
control (see Chapter 4, Routing and Output section), where altering the relative
level of a mono signal between two
stereo speakers will cause the sound
image to be perceived as moving between
them. This same relative panning effect
can be replicated for a sound source
moving between two coincident figureof-eight microphones at an angle of
90 degrees to each other. This arrangement of microphones is called a Blumlein
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pair, after Alan Blumlein, who first
experimented with these techniques in
the 1930s, and the resultant polar pickup
patterns are shown in Figure 5–4.
The Blumlein pair arrangement gives
accurate stereo imaging between two
loudspeakers of the original position of
the acoustic source. Note that the stereo
image will be reversed for sources to the
rear. Ideally, the 90 degree angle should
be maintained and all relevant sources
should be within the acceptance angle;
this is defined as the usable working area
in front of the microphone as defined by
their polar patterns, and as also used
when considering single microphones, as
already discussed in the section Microphone Directivity Patterns in Chapter 4.
Acceptance angle will therefore act to
restrict the range of possible source to
Figure 5–4. The directivity patterns of a
crossed pair of figure-of-eight microphones,
used for coincident stereo recording. The
angle of separation is 90 degrees, and
this is also known as a Blumlein pair. This
arrangement will result in the same stereo
imaging as a standard mixing desk channel
pan pot.
microphone distances that will result in
good stereo playback. The acceptance
angle for a Blumlein pair is 70 degrees.
If cardioid microphones rather than
figure-of-eights are used, the angle
between the capsules needs to be wider
in order to produce the same relative
level differences between microphones
for a given source position. This angle is
actually taken as the point at which the
response drops by 3 dB relative to the
on-axis position, and for cardioids is
defined as 131 degrees, as shown in Figure 5–5. This gives a much wider acceptance angle of 130 degrees, meaning that
the pair can be moved closer to the
source.
In practice, 90 degrees (giving an
acceptance angle of 170 degrees) is the
commonly used angle of separation for
a crossed pair of cardioids, as it is easiest to set up, although it is possible to
change this angle over a small range to
Figure 5–5. The directivity patterns of a
crossed pair of cardioid microphones, used
for coincident stereo recording. The angle
of separation for level differences equivalent to a Blumlein pair is 131 degrees.
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PRACTICAL VOICE RECORDING AND REINFORCEMENT
adjust the precise relationship between
the physical sound source positions in
front of the microphones and their perceived positions in the stereo image.
Greater than 130 degrees will leave a
“hole-in-the-middle” of the stereo field
where there will be a noticeable drop in
level and where central sound sources
will fall outside the optimal polar pickup
angle of each microphone. If the angle is
smaller than 80 degrees, the acceptance
angle becomes greater than 180 degrees,
with the small focused overlap of the
microphone directivity patterns meaning
that lateral sound sources are considerably attenuated. A coincident pair based
on hypercardioid microphones will be
halfway between a cardioid and figureof-eight, and hence the angle between
the capsules should be 105 degrees.
One problem with the crossed pair
techniques is that the center of the vocal
source is off-axis from both microphones.
This can lead to timbral coloration due
to the less-than-ideal off-axis frequency
response of the microphones. Mid-side
(M-S) recording uses one microphone to
capture the middle signal, which would
be obtained if the outputs of a stereo
crossed pair were added together. The
other microphone captures the side
signal, which would be obtained if the
output of one microphone was subtracted from the other. The most common arrangement is to use a cardioid
microphone facing forward (the mid
microphone) together with a figure-ofeight microphone (the side microphone)
facing sideways at 90 degrees, as shown
in Figure 5–6. When these M-S signals
are converted into normal left-right
stereo, they produce an identical acceptance angle to conventional crossed
cardioids.
167
Figure 5–6. The directivity patterns of a
mid-side coincident microphone arrangement. The mid microphone is a cardioid
that will be on-axis with the source (rather
than off-axis with a crossed pair). The side
microphone is a figure-of-eight. After conversion to normal stereo, this arrangement
allows manipulation of the stereo image
acceptance angle and to some extent the
balance of direct to reflected sound.
The two signals have to go through
a conversion process before being auditioned on loudspeakers or headphones
as in normal left-right stereo. The most
useful aspect of the system for everyday
recording tasks is that the acceptance
angle and hence the perceived spread of
sound sources across the stereo image
can be controlled easily from the mixing
desk or even after the recording. This
will also to some extent allow control
over the direct to lateral sound—giving
some control over the amount of reverberation received relative to the direct
sound. As the level of the mid microphone is increased relative to the side
microphone, the useful acceptance angle
and hence the perceived width of the
stereo field is increased. As the level of
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the mid microphone decreases the acceptance angle and relative stereo field
also decreases. The M-S signals are converted to conventional stereo as follows:
1. Pan the M microphone to the
center.
2. Split the S microphone to feed a
pair of adjacent channels.
3. Pan the S channels hard left and
right, phase reversing the right
channel.
4. Listen with the monitoring
switched to mono and balance the
gains of the two S channels for
minimal output.
5. Revert to stereo monitoring, and
fade up the M channel.
6. Adjust the balance between the M
and S signals for the desired image
spread.
Note that it is also possible to use
specific stereo microphones consisting
of multiple microphone diaphragms in a
single capsule, which makes the process
of setting up for a stereo recording session significantly easier. In some stereo
microphone designs the internal arrangement is fixed, in others it is variable and
some control over the stereo image will
be facilitated through external controls.
Designs exist based on both the crossed
pair technique and the M-S arrangement, with the latter giving somewhat
greater flexibility for stereo field manipulation as part of the post-recording
editing/mixing process.
Spaced Microphone Techniques
This method uses two (or more) identical but spaced microphones, each connected to a separate audio channel as
before. However, with this technique, as
the microphones are spatially separated,
a sound will arrive at each capsule at a
slightly different time according to the
relative distance between it and the
source. Hence, the spaced microphones
effectively receive time-of-arrival information, and so this technique generates
a stereo image based on timing differences (rather than level differences) and
is comparable to how ITD works with
the auditory system. However, the final
stereo image, when presented over loudspeakers, is less stable and robust when
compared with a similar coincident
recording. This is because the sound
emanating from each loudspeaker will
arrive at both left and right ears (rather
than left speaker to left ear only, right
speaker to right ear only), and there will
be a slight time delay added to the additional signal received at the opposite ear
due to the off-center positioning of each
speaker, as shown in Figure 5–7. This
additional set of ITDs imparted onto the
ITDs of the original spaced microphone
recording tends to lead to confusion in
terms of where a source is perceived to
originate from.
An additional disadvantage — although less critical in modern audio distribution—is that if the outputs from the
spaced microphones are mixed together
to produce a single mono signal, the timbre of the overall mix might be altered
due to phase cancellation effects (compare with problematic reflections when
miking a single source and how direct
and reflected path can cause the same
effects). The greater the number of combined microphones, the worse the effect is
likely to be. The big advantage of spaced
miking, however, is that this technique
allows the use of omnidirectional microphones, as the relative level of the
acoustic source and how it varies with
direction is not critical. The implication
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Figure 5–7. When listening to stereo
material using two loudspeakers, an additional set of interaural time difference
auditory cues will be imparted onto the
audio signal. This is due to the fact that the
signal from each loudspeaker will arrive at
both ears, and in each case the dotted line
path is slightly longer than the solid line
path, implying a time-of-arrival difference.
This can confuse stereo information that is
already dependent upon time differences
captured from spatially separate microphones, leading to poor stereo imaging.
of using such microphones is a significantly improved frequency response,
particularly in the low end, and a more
natural and transparent sound.
Although not necessarily accurate or
stable in terms of stereo imaging, the final
sound is normally perceived as having
width and a certain amount of imaging
information, and it usually sounds more
spacious than a coincident recording.
The recording might also suffer from a
hole-in-the-middle if the microphones
are too widely spaced apart. The simplest spaced microphone technique is to
place an identical pair of omnidirectional microphones a distance apart in
front of the sound source. A microphone
spacing of between about a half and a
169
third of the width of the actual sound
stage [the width of the source(s) that
must be recorded] is a good place to
start in terms of positioning. This could
be improved through the use of additional directional microphones to alleviate any potential hole-in-the-middle
effects. Other spaced techniques that use
directional microphones are often called
near coincident techniques because they
combine the level difference recording
characteristics of directional coincident
microphones with spaced arrays. For
instance, the ORTF method uses a pair of
cardioid microphones with a separation
angle of 110 degrees spaced about 17 cm
apart from one another.
Multiple Soloists
Working with multiple soloists is based
on an extension of the techniques introduced in the section, Single Vocal Sources,
when recording the solo voice. As with
the other applications discussed so far,
the final listeners should be first considered when approaching the problem—
what perspective will they have on the
presented sound, and what is important
for them to hear? If the multiple voices
are supposed to be heard in the context
of the space in which they are presented,
it is probably best to consider them as an
ensemble and to use a stereo recording
technique to capture the sound of the
overall event (see the section, Ensemble
Recording). However, this will generally
only apply to a limited set of possible
applications, such as classical-style music
performance, and there are a great many
other situations where clarity of direct
sound, separation, and control are more
important factors to be considered. Examples might include studio recording of
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multiple lead vocal lines, sound reinforcement of lead and backing vocals in amplified performance, interviews for radio or
television broadcast, musical theater, and
even applications such as teleconferencing. In each case, once the individual
vocal sources are captured they will be
subject to further manipulation, editing,
or studio processing post-capture.
Sources and Location
In terms of location, studio work is generally the easiest to control as there
should be enough space to separate the
vocal performers, and this can be
improved through the use of acoustic
screens. Generally, the acoustics of a studio space will not influence the final
recording too much, particularly if care
is given to source and microphone positioning, and this will of course be helped
further by using directional microphones.
The main problem to consider will be
spill from each performer bleeding into
the other microphones, so achieving
good sound source separation is important. However, problematic spill may
well be masked when placed in the context of the wider music production and
so might not be too serious a problem,
although every effort should be made to
minimize its effects. Working with multiple solo performers in an anechoic
environment will offer many of the
advantages of the studio in terms of control and clarity of direct sound. Care
should be given to the possibility of
problematic reflections, however, and
there might not be as much space available in which to arrange the vocalists
themselves. Studio based radio broadcasting will be a very similar situation
given that the environment is optimized
for the best sound for spoken voice, with
good separation between announcers/
broadcasters, and little influence from
the surrounding acoustics.
Just about every other example of
working with multiple vocal performers
will introduce problems related to the
recording environment that will have to
be considered and solved. Live sound
reinforcement work is a simple extension of the solo vocalist case, although
with every additional performer and
microphone used will come the requirement for additional foldback monitoring
and therefore another potential source of
feedback. Every separate channel of
monitoring should have a dedicated
pre-fade auxiliary send from the main
FOH mixing desk (if a separate monitoring desk is not being used) and most
importantly its own graphic EQ for
tuning out problematic frequencies.
These vary with positioning and sourcemicrophone distance, and so each microphone/monitor combination will require
its own individual EQ settings. Also the
more microphones that are used on
stage, the more spill picked up from
other off-axis sources. Therefore, noncritical microphone channels should be
muted when not in use, or noise gates
used to achieve the same effect automatically. Again, this will help to minimize
possible feedback and generally make
the mixing process easier. Obviously,
directional microphones should be used
at all times.
Other forms of broadcasting, particularly those based in television studios,
will make use of lavalier/lapel/tie-clip
microphones to ensure good capture
of direct sound from each individual.
Care should be taken in positioning
the microphone well. The “tie” position
works best, as it will center the microphone with the mouth, although it
should not be so high that the chin shad-
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PRACTICAL VOICE RECORDING AND REINFORCEMENT
ows the microphone, perhaps when the
person’s head moves to read written
notes. Generally, such microphones also
have a rolled off bass-response to take
care of possible proximity effects if it has
a cardioid family directivity pattern, and
to compensate for a possible bass-rise
from the resonance of the person’s chest
cavity. Similarly, the high end may be
boosted slightly to compensate for the
microphone being positioned off-axis. In
general, once attached, the resulting
sound should be checked for any major
problems or variability as the talker goes
about his regular business. This should
include checking that the microphone
sound/positioning is not affected by the
subject’s normal movements.
These types of microphones, usually
mounted in a headset, are also used
extensively in theater productions (especially musical theater) where the challenge is to get good sound from each
actor while keeping the microphone and
cables out of sight as much as possible.
They are often only used for the principal performers, and so for capturing, for
instance, the chorus or other on-stage
sound, shotgun microphones are arranged around the edge of the stage to
give good overall coverage. Graphic EQ
might again have to be used to minimize
feedback, although the levels involved
are generally considerably less than
amplified sound reinforcement and so
are less of a problem. Another type of
microphone used in this and similar
vocal applications is the boundary microphone — sometimes also called a float.
These microphones generally have a
hemispherical (half omnidirectional)
pickup pattern and are designed to be
mounted on a flat surface (such as the
front stage area or a wall). They operate
on a different principle from the micro-
171
phones introduced so far (although they
are generally a condenser type design)
and use the acoustics of direct and
reflected sound at a surface to give effective rejection of nondirect/reflected
sound in favor of direct sound only (and
hence will also help to minimize feedback problems). However, despite their
good rejection of background sound,
given their almost omnidirectional behavior, they should be used with care in
terms of source pickup, applied gain, and
possible feedback. Also, as they have to
be physically placed on a wall or floor,
they will be subject to possible mechanical vibrations from, for instance, footsteps.
In research applications, if multiple
talkers or singers must be captured
simultaneously, with clarity, separation,
and accuracy being the important influencing factors, probably the only option
available is to use headset microphones.
If the recording location is large, with a
controlled acoustic such that good separation can be achieved and reflections
and spill minimized, there may be more
options available, and the use of spaced
omnidirectional microphones (favored
for research applications) might be possible. However, this is generally unlikely
given that the favored space for this
approach would be a large anechoic
chamber. Generally then, the headset
method is perhaps the best way forward
and has been reported as being successful in a number of studies. Note that
additional microphones may be required
to ensure that the headset microphones
are calibrated correctly, as detailed in the
section Recording for Research.
Where there is a requirement to capture multiple talkers and individual
lavalier/headset microphones are not
practical or possible, a simple one-toone arrangement of spaced directional
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microphones is probably the best option.
This may be used for instance in roundtable style conference presentations, or
in multiple talker teleconferencing. In
the latter application, if source separation is not critical a single (for mono) or
multiply arranged (for stereo) boundary
microphones placed appropriately will
provide a good compromise. As with
theater sound, care should be taken to
avoid possible sources of mechanical
vibrations that will be captured due to the
microphone being directly placed on a
local surface—typically a tabletop in this
case—with drumming fingers or moving
papers, pens, etc., being obvious sources.
Potential Problems
In the majority of these applications, the
purpose of the sound system used is to
ensure that the direct sound is captured
in such a way that is it clear and separate
from background sounds, particularly
the other sources present in the local
vicinity, so that control can be obtained
over each individual source. However,
as soon as more that one microphone
is used—for even a single source—then
the application verges on being a spaced
stereo recording, even if single channel
capture is the required outcome. This
means that the related problems already
discussed in this and the previous chapter are combined and must be considered
and dealt with. These can be summarized as follows.
Omnidirectional vs. cardioid family.
Omnis will give a flat frequency response
and transparent sound at the expense of
loss of separation and increased spill
and background sound (including reverberation and reflections). Cardioid family microphones will improve separation
and reject nondirect sound but poten-
tially alter the timbre of the captured
vocal source.
Source separation and background
noise. Priority is given to the capture of
the individual direct voice source and
rejection of background noise to facilitate maximum control of individual
sources. However, no microphone is
ideal, and every microphone added to a
particular scenario will capture every
source present to some degree, reducing
separation and ultimately compromising control.
Off-axis colorization. Nondirect sounds
will be captured off-axis by other nearby
microphones. The off-axis frequency
response of a directional microphone is
not at all ideal, leading to potential timbral colorization problems when multiple channels are summed or auditioned
together—giving a total result that consists of optimal on-axis direct sound
from the source microphone, together
with colored, off-axis spill captured from
another adjacent microphone.
Phase cancellation effects. Spaced mi-
crophones imply captured timing differences for a particular source. This may
lead to phase cancellation based timbral
colorization due to the delay between
signals when summed or auditioned
together and/or confused stereo imaging.
This problem will be more pronounced if
there are major reflections also present.
As a helpful guideline, wherever
possible, aim to have the distance between spaced microphones at least three
(and preferably closer to five) times that
of the individual source-microphone
distance. In summary, maintaining good
separation is the key to achieving a good
recording or good sound in these and
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other similar multiple solo source scenarios. Time, experimentation, and positioning will all help in this regard and
ultimately provide greater flexibility,
control, and creative options in editing,
mixing, and post-production stages.
Ensemble Recording
Ensemble recording here refers to the
capture of vocalists performing in a particular venue. Source separation is not
the key focus; rather, priority is given to
the accurate and transparent capture of
the whole sound event, to include all
performers, their relative balance, blend,
and spatial positioning, and the acoustics of the venue itself. The most common example of where these techniques
are appropriate would be choral recording, although this may include much
smaller ensembles such as a barbershop
quartet or the performance of spoken
word. Note, however, that with smaller
ensembles, production or aesthetic preferences may dictate that they should be
recorded as multiple individual sources,
as discussed in the previous section,
rather than as a natural whole ensemble.
Sound reinforcement is less common,
as ensembles are sized for the material
and space in which they will be heard,
although individual microphones may
be used to help soloists as part of the
wider group (for instance spoken narration plus choral performance), and the
use of such spot microphones will be considered as part of this section. In this
context, the ensemble considered will also
include solo performers where individual close-up miking is less appropriate
and the sound in its totality in combination with the space is the desired result.
Ultimately, what is being attempted is
173
the capture and permanent recording of
a particular sonic event so that the listener hears what the audience would
have heard in the venue (often in the
best seat) during the performance itself.
Hence, stereo microphone techniques
are the primary method of realizing this
desire.
Source and Location
In general, the aim is to arrange the
ensemble around the stereo microphone
arrangement in such a way that they
occupy the complete stereo image, or
rather to place the microphones so that
they capture the complete stereo sound
stage. Considering a large choir, as might
be found accompanying an orchestra, as
the vocal ensemble source, coincident
crossed cardioids might be best placed
above and close to the conductor position in order to achieve the desired
stereo image width. However, a Blumlein pair of crossed figure-of-eights
would have to be positioned a long way
down the venue, much further away
from the choir, to achieve the same
stereo width due to their narrower
acceptance angle of 70 degrees. In choosing the polar patterns for the stereo
microphone arrangement, the physical
separation between sound sources and
microphones is determined for a given
stereo width and therefore the listener’s
perspective of the recording.
In this example the cardioids would
give a very close-perspective sound,
with little reverberation, due to both
close positioning and directivity pattern
influenced rear rejection, and a distorted
choral balance favoring those singers
closer to the front and more centrally
positioned. The figure-of-eights would
give a much more natural and balanced
perspective to the choir, but would also
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capture a great deal of the reverberant
sound, due to both their positioning and
their increased rear pickup, which might
make the recording rather more distant
than anticipated. A compromise solution
might use crossed hypercardioid mikes
at some midpoint between cardioid and
figure-of-eight extremes, or a scattering
of close spot microphones to reinforce
the weaker sections of the choir.
Microphone Positioning
As a starting point, the most commonly
used method and easiest to get good
results while still allowing a degree of
experimentation is the crossed pair.
These should be good quality cardioid
condenser microphones, positioned one
above the other, angled at between 90
and 120 degrees, according to source
width. As mentioned above, they will
also help to cut down on the amount of
reverberation captured in the recording,
due to the null pickup point at their rear.
In general, a good level of direct sound
compared with the reverberant sound is
required to ensure overall clarity. Placing
the microphones in a typical audience
seat location will usually result in too
much reverb when auditioned over
loudspeakers. Experiment with distance
to achieve the best balance between
closeness/clarity and liveness/reverberance. It helps when setting sourcemicrophone distance to have an estimate
of the critical distance/reverberation
radius of the space where direct and
reverberant sound for a particular source
are theoretically balanced. Clearly, the
microphones should not be placed
beyond this distance. It obviously helps
when experimenting with position in
this way to be able to listen directly to
the results from the microphones to aid
the decision-making process. If possible,
stereo loudspeakers in a separate control
room should be used, although realistically for most scenarios, good headphone (preferably enclosed) listening
will be the main method of monitoring
the microphone signals.
Once an optimum distance for the
microphones has been decided the stereo
imaging produced by the coincident pair
should be considered. Monitor the performers over headphones and listen to
make sure that what is heard agrees with
what can be seen and heard in the actual
venue. If the stereo spread is either too
wide or too narrow, then the angle of
separation (and hence the acceptance
angle) can be adjusted. If the stereo
image appears off-center, ensure that
gain levels are equal for both microphone channels and that they are pointing in the appropriate direction. If possible, before the performers enter the
venue, make a recording of someone
walking across the front of the performance area from stage left to stage right
and listen back to the result to make
sure the recorded stereo imaging is in
good agreement.
Always use stands that give good
stability and allow the microphones to
be raised to a good, high level. Raising
or lowering the microphones in this
manner can also achieve a good balance
between any soloists and the accompanying ensemble if this is required, or
the ensemble as a whole if it consists
of many people. Use shock mounts
wherever possible to minimize possible
noise from vibrations, or place the
stands on some rubber or sponge mats
to decouple them from the floor of
the venue (carpet tiles can also be useful). A good starting position in terms
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of microphone distance and height is
about 12 feet from the performers and
about 12 feet above the floor.
Potential Problems
If it is not possible to achieve an optimum
balance between direct and reflected
sound or stereo width due to limitations
of time in setting up or restrictions in
terms of microphone positioning, a combination technique might have to be
used. This consists of a main stereo pair
together with individual spot microphones. This technique is also appropriate
if additional minimal sound reinforcement is required for particular aspects of
the ensemble or for soloists working
with them in combination, or if an omnidirectional spaced pair is used as the
main microphone arrangement resulting
in a hole-in-the-middle stereo imaging
problem. A spot microphone is basically
a close-up microphone used in combination with a more distanced main stereo
pair to reinforce or generally improve
the overall balance of sound sources.
There are three things to consider with
this combination technique.
Image position. The main microphone
pair will establish stereo image positions
for each aspect of the ensemble, and the
close-up spot microphones should not
contradict this virtual sound stage.
Hence, each spot microphone must be
panned appropriately to match the main
stereo mix. The best technique for setting the individual pan positions is to
concentrate on the stereo image of a particular vocal part from the main stereo
pair, then slowly fade up the corresponding spot microphone, paying particular
attention to how the image moves in the
stereo field as this happens. If the image
175
pulls to the right, fade the spot microphone down, adjust the pan control
slightly more to the left, and try again.
Repeat until the pan position of the spot
microphone is in agreement with the
main stereo pair.
Perspective. A microphone close to the
vocal source will have a completely different perspective to one much further
away. This contrast is usually undesirable as it will draw undue attention to
the soloist in question. The relative balance between the direct sound from the
spot microphone and the overall directplus-reverberation mix from the main
pair is critical. If the signal from the spot
microphone is too noticeable then it is
too high in the overall mix.
Timing. Note that this is usually only a
problem with very large recording venues. Consider again the recording of a
large choir in a large venue where the
main stereo microphones may be 50 feet
away from the main ensemble. Sound
travels at approximately one foot per
millisecond (ms), and so the signal from
the stereo pair will be delayed by about
50 ms relative to any close spot microphones. Therefore, to ensure that closeup and distant microphones are in
agreement, the spot microphones must
be delayed by the appropriate amount,
usually at the editing or mixing stage. It
is therefore important in this case to
measure source-microphone distances,
and if appropriate, the temperature of
the venue, which will help to give a
good estimate of the speed of sound.
From this a time delay can be calculated,
with final adjustments made by ear to
suit (see Chapter 1, section Sound Transmission and Velocity, and some of the
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suggested further reading for more
information relating to how the speed of
sound varies with temperature and how
this calculation would be performed).
Finally, if the stereo pair used, for
whatever reason, tends to favor the
direct sound from the ensemble, resulting in a slightly too close perspective,
some additional control over the reverberation can be facilitated through the
use of two additional spaced “ambient”
microphones. These microphones should
be placed beyond the critical distance
of the space, with generally a spaced
arrangement giving better results than
a similar coincident pair, and they are
used to capture the more reverberant
sound of the venue. Once in place, they
should be balanced up with the more
direct coincident pair to give more control over direct/reverberant perspective
of the finished result. However, both this
and spot miking methods do add to
the complexity of the overall recording
(a mixing desk or multitrack recording
system will be required rather than a
two-track direct to stereo device), and so
it is usually best to experiment with the
main stereo pair to get the best sound,
balance, and perspective that is possible
for a particular source/location/listener
combination.
Background Vocals in
Popular Music
Background vocals in studio recording
work are sometimes dealt with somewhat
differently from what has been considered so far and are therefore considered
separately here. Note that background
vocals in amplified sound reinforcement
applications should be treated as individual soloists for clarity, separation,
control, and minimization of feedback.
This may also apply in the studio according to production or aesthetic considerations. However, it is generally assumed
that in studio work there will be adequate
control over the acoustics of the actual
recording space and so a little more flexibility is allowed.
General background vocals (sometimes called “gang” vocals) involve
grouping a number of performers around
a single microphone rather than miking
individually. This helps to provide a uniformity of sound, will give a particular
energy to the recorded music, and
allows the vocalists to interact with one
another for the sake of the overall performance. A cardioid microphone, preferably a condenser, can be used for this,
but the limitations of the acceptance
angle and the possibility of off-axis colorization should be considered. As a
result, there should be no more than two
or three vocalists grouped in an arc
around the front of the microphone. If
the acoustics of the studio environment
allow it, an omnidirectional directivity
pattern would be ideal, providing a
more transparent sound and allowing
many more vocalists to be arranged
around the microphone in a circle at an
equal distance. As with stereo recording,
the source-microphone distance in either
configuration will alter the overall sense
of perspective of the ensemble when
auditioned.
If further stereo control is required to
further enhance the overall production,
it is relatively simple to replace the cardioid/omni with a coincident pair. The
next level of improved separation and
control would be to record each vocalist
individually and at the same time. In this
situation hypercardioid microphones
will help to focus in on each individual
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PRACTICAL VOICE RECORDING AND REINFORCEMENT
performer, and acoustic screens should
be used if available. As with any technique involving multiple spaced microphones, the possibility of spill and phase
cancellation effects should be considered,
but this will allow individual panning of
each source while helping to maintain
the group vocal feel. Of course, the final
level of control would be to record each
vocalist separately and deal with them
as any other solo vocal performer.
SUMMARY
This chapter has considered a wide variety of vocal recording and sound reinforcement applications and how they
should be approached to achieve the best
results. The definition of what might be
“best” varies from case to case but should
similarly be defined on a case-by-case
basis through due consideration of the
nature of the sound source, the environment in which it is being recorded, and
perhaps most importantly of all, the
demands or reasoning behind the final
listening experience. There are many different scenarios where a vocalist has to
work with a microphone and associated
audio system, and a distinction has been
made between single or multiple vocal
sources. The particular demands of
recording for vocal research have also
been considered. Single source work
introduces the importance of capturing
the direct sound from the source while
minimizing spill, background noise,
reverberation, and/or feedback, with
the implication this has for clarity, separation, and control over the final result.
Ensemble vocal work introduces the use
of stereo recording techniques and the
importance of recording a complete
177
sound event in such a way that what the
final listeners hear is a true representation of what they would have heard had
they sat in the best seat in the house during the event. It should also be clear that
this is a somewhat artificial delineation,
as there are some scenarios that fall into
both camps—for instance, recording a
solo singer in a good concert hall.
It is important to note that the contents of this chapter should be considered as guidelines, rather than rules.
Generally, there are no hard and fast
rules when it comes to recording—the
ultimate deciding factor is that the final
result should sound “good.” Again, the
definition of good is highly subjective
and will also vary according to the particular recording task. Making quality
recordings for research purposes is a
particular example here, although objective measures can also be applied to
some extent in this case to determine the
final quality of the results obtained. Some
of the most important points to take away
from this chapter actually have nothing
to do with microphones and audio systems at all, but have everything to do
with being a good sound engineer:
■ Plan for the recording session as
much as possible beforehand.
■ Anticipate potential problems and
possible appropriate solutions.
■ Allow plenty of time to set up.
■ Know the audio system well to get
the best from it.
■ Test all aspects of the system prior to
the start of the session.
■ Approach problems in a methodical
and logical manner and consider
possible alternative solutions before
deciding on a course of action.
■ Experiment to the get best results
out of a particular setup or scenario.
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■ Respect the performers/artists,
communicate effectively with them,
and consider their own opinions in
order to achieve the best possible
results.
And finally, at all times listen carefully to the audio material: develop your
listening skills, learn to trust your ears,
and make an honest evaluation as to the
quality of the final results in a bid to
make even better vocal recordings in
the future.
FURTHER READING
Bartlett. B., & Bartlett, J. (2005). Practical
recording techniques: The step-by-step approach
to professional studio recording (4th ed.).
Oxford, UK: Focal Press.
Eargle, J. (2004). The microphone book: From
mono to stereo to surround—A guide to
microphone design and application (2nd ed.).
Oxford, UK: Focal Press.
Granqvist, S., & Svec, J. G. (2005, September).
Microphones and room acoustics and their
influence on voice signals. Paper presented at
PEVoC 6, London Retrieved from http://
www.speech.kth.se/~svante/Granqvist_
Svec_PEVoC6_Microphones.ppt
Howard, D. M., & Angus, J. A. S. (2006).
Acoustics and psychoacoustics (3rd ed.).
Oxford, UK: Focal Press.
Hugonnet, C., & Walder, P. (1998). Stereophonic sound recording, Theory and practice.
Chichester, UK: John Wiley and Sons.
Jers, H., & Ternström, S. (2004, June). Intonation analysis of a multi-channel choir recording. Paper presented at the Baltic-Nordic
Acoustics Meeting, Mariehamn, Åland,
Finland.
Rumsey, F., & McCormick, T. (2005). Sound
and recording—An introduction (5th ed.).
Oxford, UK: Focal Press.
Talbot-Smith, M. (2004). Sound engineering explained (2nd ed.). Oxford, UK: Focal Press.
Talbot-Smith, M. (2004). Sound engineer’s pocket
book (2nd ed.). Oxford, UK: Focal Press.
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