User manual | Efficient filter for artificial ambience

US008634568B2
(12) United States Patent
(10) Patent N0.:
(45) Date of Patent:
Neoran et a].
(54)
FOREIGN PATENT DOCUMENTS
EFFICIENT FILTER FOR ARTIFICIAL
AMBIENCE
SE
0202159-0
(75) Inventors: Itai Neoran, Beit-Hannanya (IL); Meir
Niimi K., et al “A new digital reverberation With excellent control
Aviv (IL)
capability of early re?ections” Audio Engineering Society 74”’ Con
ven?on,(1983)pp.1-24.
(73) Assignee: Waves Audio Ltd., Tel Aviv (IL)
Notice:
Jot J .M. et al “Digital delay networks for designing arti?cial
reverberators” Audio Engineering Society 90”’ Convention, (1991)
Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
p.1-16.
Blaubert J., “Spatial hearing” MIT press (1997) pp. 276-279, 348
358.
U.S.C. 154(b) by 267 days.
Begault D.R., “3-D sound for virtual reality and multimedia” AP
professional (1994), pp. 45-46, 99-111, 175-190.
(21) Appl. No.: 12/966,729
(22)
Filed:
M. Karjalainen et al “More about this reverberation science” Audio
Engineering Society 111th Convention, (2001) pp. 1-8.
Dec. 13, 2010
(65)
Y. Grenier et al “Extraction of Weak background transients from
audio signals” Audio Engineering Society 114th Convention, (2003)
pp.1-10.
Prior Publication Data
US 2011/0081025 A1
7/2002
OTHER PUBLICATIONS
Shashoua, Tel Aviv (IL); Yoad Nevo, Tel
(*)
US 8,634,568 B2
Jan.21,2014
S. Molla et al “Determining local transients of audio signal, White
paper by LATP” CMI, Marseille, France (2004) pp. 1-4.
Apr. 7, 2011
Gardner M.B. “Historical background of the Haas and or precedence
effect” J. ofAcoustical Society ofAmerica, No. 43 (1968) pp. 1243
1247.
Related US. Application Data
D. Griesinger “Practical processors and programs for digital rever
(63)
Continuation of application No. 11/ 179,510, ?led on
Jul. 13, 2005, noW Pat. No. 7,876,909.
beration” Audio Engineering Society 7”’ Convention, (1989) pp. 187
(60)
Provisional application No. 60/587,047, ?led on Jul.
13, 2004.
Primary Examiner * Duc Nguyen
Assistant Examiner * George Monikang
Int. Cl.
PLLC
195.
(74) Attorney, Agent, or FirmiBrowdy and Neimark,
(51)
(52)
G10K 15/12
(2006.01)
G10H1/16
(2006.01)
(57)
ABSTRACT
A circuit, method, and system for producing arti?cial ambi
US. Cl.
USPC .............................. .. 381/63; 381/61; 381/118
(58)
ence effect for an input audio signal, mono, stereo, or sur
Field of Classi?cation Search
USPC
round. The ambience effect enhances arti?cial reverberation,
replaces arti?cial reverberation, or synthesizes extra audio
channels, such as surround channels. The circuit may include
........... .. 381/61-63,66,118,119,94.1-94.5,
381/94.8
a transient reduction module and a reverberation ?lter. The
See application ?le for complete search history.
transient reduction module may be adapted to reduce tran
(56)
sients in an input audio signal of one or more channels. The
References Cited
reverberation ?lter maybe adapted to receive a transient-re
duced signal of one or more channels corresponding to the
U.S. PATENT DOCUMENTS
transient-reduced signal.
4,584,700 A
6,215,408 B1
4/1986 ScholZ
4/2001 Leonard et al.
22 Claims, 9 Drawing Sheets
Transient
reduoed signal
Input
Audio signal :
(N channels)
Transient
Reduction
/
1;
N channels
Rsvarh
Filter
210
220
230
Output
——
per-channel
:Brtificial
/ 240
gain and adder
200
ambience signal
(H channels)
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2
EFFICIENT FILTER FOR ARTIFICIAL
AMBIENCE
[6] Y. Grenier & B. David, Extraction of Weak background
RELATED APPLICATIONS
[7] S. Molla & B. Torresani, Determining local transients of
The present application is a continuation application of
application Ser. No. 11/179,510, ?led Jan. 13, 2005, Which
application claims the bene?t of US. Provisional Appln. No.
France, 2004
[8] Gardner M. B, Historical background of the Haas and or
precedence effect, I. ofAcoustical Society ofAmerica, No.
43, 1968.
[9] D. GriesingeriPractical processors and programs for
transients from audio signals, Audio Engineering Society
1 14th convention, 2003
audio signal, White paper by LATP, CMI, Marseille,
60/587,047, ?led Jul. 13, 2004, the entirety of both applica
tion being expressly incorporated by reference herein.
digital reverberation, Engineering Society 7”’ conference,
1 989.
FIELD OF THE INVENTION
Arti?cial reverberation is a popular method for enhancing
audio production and reproduction in mono, stereo, and sur
The present invention relates to producing an arti?cial
ambience effect for an input audio signal, mono, stereo, or
surround. The ambience effect is intended for example to
enhance arti?cial reverberation, to replace arti?cial rever
round sound. This process attempts to simulate an acoustic
space surrounding the sound-source. This is done by applying
a synthetic reverberation ?lter (linear or non-linear) to the
audio signal, giving rise to a reverbed signal simulating
beration, or to synthesiZe extra audio channels, for example
surround channels.
re?ections arriving from Walls or objects in an imaginary
20 room.
In real room acoustics, suppose a pressure impulse is emit
ted from a sound source and reaches a point Where the sound
is collected or heard. This direct sound arrival is subject to a
BACKGROUND OF THE INVENTION
Provided beloW is a list of conventional terms. For each of
the terms beloW a short de?nition is provided in accordance
With each of the term’s conventional meaning in the art. The
terms provided beloW are knoWn in the art and the folloWing
de?nitions are provided for convenience purposes. Accord
ingly, unless stated otherWise, the de?nitions beloW shall not
be binding and the folloWing terms should be construed in
accordance With their usual and acceptable meaning in the art.
time delay, attenuation, and ?lter, relating to the relative posi
25
tions of the source and listener. The original pressure impulse
is also re?ected from Walls and objects in the room, and then
arrives to the listener point With additional time delay, attenu
ation, and ?ltering. The secondary arrivals are called “re?ec
tions”, and can be seen as discrete peaks in the impulse
30
response of the overall acoustic ?lter. The order of a re?ection
is de?ned as the number of times it hits a Wall or object before
arriving to a de?ned destination (e.g., a listener). After a
Reverberation (?lter)iA linear or non-linear ?lter
adapted to create a simulation of acoustic behavior Within a
(certain) surrounding space, typically, but not necessarily,
including simulation of re?ections from Walls and objects.
Some kinds of reverberation ?lters may implement convolu
tion of the input signal or preprocessed derivative of the input
35
certain time in the impulse response, and beyond a certain
order of re?ection, the density of the re?ections and their
overlap increases so much that they are no longer perceived as
separate and can only be referred to through their statistical
properties and frequency content [3, 4].
signal With pre-recorded impulse-response.
Re?ectionsiThe sequence of arrivals to the listener of a
In a common arti?cial reverberation ?lter the synthetic
pressure impulse emitted in an acoustic space, bouncing back
from Walls and objects in the space. In arti?cial reverberation
re?ections are implemented as continuous segments of one or
40
taps, each segment simulating the impulse response of a
re?ected replica of the sound.
TransientiRapid changes in a signal’s properties such as
intensity, frequency content, or statistical measures.
45
Transient detectioniFor a set of time points t:T1 . . . Tn in
an input signal S(t) a transient detection is an estimation
function T(t) of the amount of transient for every time
t:T1
. . . Tn.
Transient reductioniSuppression of transients in a signal
more non-Zero FIR ?lter taps [1,4], and/or IIR ?lters [2,4], or
a combination, in both cases With sloWly decaying impulse
responses. A human’s perception of space is guided by the
relative delays betWeen the direct sound and the re?ections,
?ltersire?ections are continuous segments of non-Zero ?lter
50
and, in the case of a stereo signal, by the difference and
correlation betWeen the left channel re?ections and the right
channel re?ections [3, 9]. Generally, When applying such a
reverberation ?lter to a sound input, and then summing it in
some relative level to the input (simulating the direct sound
path), the results tend to sound Wider and more spacious than
the original.
Many attempts have been made to produce arti?cial rever
using a non-linear process.
berations in a manner to create a sense of ambience Which is
typical of different environments. Unfortunately, in the prior
RELATED ART
[1] Niimi K., Fujino T., ShimiZuY., A neW digital reverbera
tion With excellent control capability of early re?ections.
55
Audio Engineering Society 74”’ Convention, 1983.
[2] Jot J. M., Chaigne A., Digital delay netWorks for design
ing arti?cial reverberators, Audio Engineering Society 90th
convention, 1991.
[3] Blaubert 1., Spatial hearing, MIT press 1997, pp 276-279,
amounts of resources are needed. Considering that the
impulse response of a typical concert-hall reverberation (for
example see FIG. 1) is very long (a feW seconds until it decays
60
348-358.
tion, 2001
to an inaudible level), then the number of re?ections in it is
very large. The quality of the perceived effect of an arti?cial
imitation tightly depends on the number and the density of the
[4] Begault D. R., 3-D sound for virtual reality and multime
dia, AP professional 1994, pp 45-46, 99-111, 175-190.
[5] M. Karjalainen & H. Jarvelainen, More about this rever
beration science, Audio Engineering Society 1 1 1th conven
art credible arti?cial reverberation is considered a very heavy
computational task, and in order to produce a credible sense
of ambience typical of some environments, considerable
simulated re?ections. Therefore, in order to achieve a cred
ible sense of ambience typical of a concert hall a large number
65
of non-Zero ?lter taps is required (for a non-limiting simpli
?ed example see FIG. 2, shoWing an impulse-response of a
reverberation ?lter simulating only the major non-Zero taps of
US 8,634,568 B2
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4
the natural ?lter). If the synthetic re?ections in a reverberation
?lter are not dense enough, in time and/or in frequency, an
the frequency domain, dynamically controlled by the amount
unpleasant comb-?lter is perceived [4, 5, 9]. Beyond a certain
tors and/or processors have not been used in the context of
arti?cial reverberation, as is described in some embodiments
of detected transient. HoWever in the prior art, transient detec
time gap betWeen the re?ections, they are perceived as dis
crete echoes [4, 9]. The presence of discrete echoes in a
concert hall acoustics (for example) is considered bad, as it
deteriorates intelligibility and attracts attention aWay from
the instrumental and vocal direct sources. Therefore, prior art
of this present invention.
When considering a reverberation ?lter, Whether natural or
arti?cial, it is possible to separate the part of the ?lter that
contains the re?ections from the part that contains the direct
synthetic reverberation ?lter designs commonly use FIR ?l
sound, and examine them as tWo separate ?lters that are
summed in the output. One can notice that strong transients
ters having a large number of non-Zero ?lter taps, and/or IIR
?lters having complex structures, to simulate a high re?ec
can be problematic in the output of the re?ections part of
reverberation ?lters, as they alloW the listener to perceive
tions density.
In the same time, the larger the room/hall is, the greater the
individual re?ections as echoes. In the same time, transients
are not essential at the output of the re?ections part of rever
delay gap betWeen the re?ections as can be seen from the
folloWing equation [eq. 1, see ref 3]:
beration ?lters, natural or arti?cial, for three reasons: Firstly,
many reverberation ?lters contain a direct signal path
Number of re?ections per second:4*PI*(C”3)*(l‘2)/ V
betWeen the input and the output, representing the acoustic
When c is the speed of sound and V is the room volume.
Indeed, discrete echoes Would have been heard in concert
halls if the hall designers hadn’t put much effort in breaking
up those echoes into many smaller re?ections by using acous
tic panels and other objects. Thus, to design a synthetic rever
beration ?lter simulating large hall acoustics, While not
increasing the total computational effort, the prior art is many
direct path betWeen the source and the listener, and the tran
sients are preserved in this path. Secondly, in many reverbera
20
results in smearing in the output of input transients [9].
times forced to use more time-delay betWeen non-Zero ?lter 25
taps, causing more time-domain artifacts to be noticeable.
In addition, the early re?ections, from the direct (?rst)
arrival up-to approximately 50-80 milliseconds later, contrib
There is thus a need in the art, for a system and method of
30
e?iciently producing enhanced arti?cial reverberations.
There is a further need in the art, for a system and a method of
reverberation ?lter designer cannot rely on just the early part
of the impulse-response and is usually forced to implement
e?iciently producing enhanced arti?cial reverberations,
requiring a less computationally expensive reverberation ?l
complex ?lter structures having an impulse response in Which
peak density increases With time, simulating a continuously
increasing re?ections density, for example see [5].
Thirdly, When a reverberation ?lter is used to enhance sound
that is intended to be reproduced in a direction other than the
direction of the source (for example rear surround audio
channels Where the musical instruments are in the front), then
the listener expects to hear less transients in those channels
simply since they contain no direct path.
ute less to the perceived spaciousness and more to the sense of
distance and localiZation [2, 9]. Thus, to obtain the effect of a
large concert hall and for an increased spaciousness, the
tion ?lters, just as in many real rooms and halls, the re?ections
part of the ?lter is very dense With re?ections (diffused) and
ter. There is yet a further need in the art, for a system and a
35
method of ef?ciently producing enhanced arti?cial reverbera
tions, Wherein reduction of transients is used to reduce the
amount of perceived echoes in the output, or to maintain the
On the other hand, “transients” are rapid changes in a
signal’s properties such as intensity, frequency content, or
amount of perceived echoes While loWering the density and/
statistical measures. When the sound source is a short impulse
or number of synthetic re?ections.
(like hand clapping), the result through the room/hall acoustic
40
SUMMARY OF THE INVENTION
?lter is a sequence of transients that relate to the individual
re?ections. The higher the re?ections density, the less the
Some embodiments of the present invention relate to a
circuit, a method and a system for producing arti?cial ambi
transients are perceived, since the re?ections merge into one
continuous statistical behavior and since in the reverberation
?lter, the intensity changes betWeen the re?ections in the
impulse response and the frequency response changes
45
betWeen the re?ections are too close in time to be separated by
our hearing system Which then perceives them as a part of a
continuous ?lter frequency response [4]. By breaking large
re?ections into many small ones, acoustic designers are able
to loWer the amount of transient in important parts of the
50
acoustic impulse response.
There exist methods in prior art for detection of transients
in audio and for their manipulation. Transient detectors pro
vide an estimation of presence or amount of transient T(t) in
55
a signal S(t) for set of time points tITl . . . Tn. Transient
transient-reduced signal comprised of one or more channels
and to produce a reverbed signal comprised of one or more
In accordance With further embodiments of the present
invention, the transient reduction module may be adapted to
60
of transient relates to the amount and rapidity of changes in
the signals intensity, frequency content, and/or statistical
properties, and different transient detectors focus on detect
ing one or more of the latter properties. When the amount of
transient is detected, the information may be used to intensify
the transient or to suppress it. This can be done by processing
the original signal through a gain, a set of gains, a ?lter, or in
ambience. In accordance With some embodiments of the
present invention, the circuit may include a transient reduc
tion module and a reverberation ?lter. In accordance With
some embodiments of the present invention, the transient
reduction module may be adapted to reduce transients in an
input audio signal comprised of one or more channels. In
accordance With further embodiments of the present inven
tion the reverberation ?lter may be adapted to receive the
channels corresponding to the transient-reduced signal.
detectors for audio can be found for example in [6, 7]. Detect
ing a transient in an audio signal is essentially a process Which
includes computing an estimation of the amount of transient
present in a signal or a frequency band of a signal. The amount
ence. In accordance With some embodiments of the present
invention, there is provided a circuit for producing arti?cial
affect the input audio signal in a manner to decrease the
amount of discrete echoes in the reverbed signal. In accor
dance With yet further embodiments of the present invention,
all other things being equal, the transient reduction module
65
may be adapted to affect the input audio signal in a manner to
enable the reverberation ?lter to utiliZe a substantially smaller
number of taps, Without substantially increasing the presence
of discrete echoes in the reverbed signal.
US 8,634,568 B2
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6
In accordance With some embodiments of the present
invention, circuit may further include a gain and an adder for
each reverbed signal channel. In accordance With some
to calculate an absolute value of a mathematical representa
embodiments of the present invention, each of said gains may
be coupled to a reverbed signal channel and may be adapted
value module may be adapted to determine Which of the one
to amplify or to attenuate the reverbed signal channel. Each of
lute value modules is the highest. In accordance With further
tion associated With the audio input channel With Which that
absolute value module is associated. The second maximum
or more absolute values calculated by the one or more abso
the one or more adders may be connected to one of the gains
embodiments of the present invention, the envelope detector
and to one of the input signal channels and may be adapted to
sum the output of the ampli?ed or attenuated reverbed signal
channel to a corresponding input signal channel
In accordance With some embodiments of the present
invention, the transients reduction module may include a
module may be adapted to receive from the second maximum
value module the highest absolute value.
In accordance With further embodiments of the present
invention, there is provided a method of producing arti?cial
transient detection module, a processing module and one or
present invention, the method may include receiving an input
ambience. In accordance With some embodiments of the
more gains and/or one or more ?lters. In accordance With
audio signal comprised of one or more audio channels. Once
some embodiments of the present invention, the transient
detection module may be adapted to detect the presence of
received, transient in the input audio signal may be reduced,
transients in an audio signal comprised of one or more chan
nels and to calculate for each detected transient a transient
more channels. The transient-reduced signal may be applied
giving rise to a transient-reduced signal comprised of one or
to a reverberation ?lter, giving rise to a reverbed signal com
value corresponding to the acoustical properties of the tran
sient. In accordance With some embodiments of the present
prised of one or more channels.
20
invention the processing module may be adapted to calculate
for each transient value a corresponding gain and/or ?lter
BRIEF DESCRIPTION OF THE DRAWINGS
value. In accordance With some embodiments of the present
For a better understanding, the invention Will noW be
invention, the one or more gains and/or one or more ?lters
described by Way of example only With reference to the
may be operatively coupled to the processing module. The
25
accompanying draWings, in Which:
one or more gains and/or the one or more ?lters may be
FIG. 1 is a graphical illustration of a natural acoustic
adapted to amplify and/ or to attenuate the input audio signal
impulse response of a typical concert-hall (one channel, only
a part of the impulse response);
comprised of one or more channels in accordance With a gain
and/ or ?lter value received from the processing module.
In accordance With further embodiments of the present
invention, the transient reduction module and the reverbera
30
FIG. 2 is a graphical illustration of an exemplary impulse
response of a prior-art synthetic reverberation ?lter simulat
ing only the major non-Zero taps of the natural ?lter illustrated
tion ?lter may be interchanged, such that the input audio
signal may be ?rst applied to the reverberation ?lter, and the
in FIG. 1;
transient reduction module may be fed With the reverbed
ducing arti?cial ambience, in accordance With some embodi
ments of the present invention;
signal thereby reducing transients in the reverbed signal.
In accordance With some embodiments of the present
invention, the transient reduction module may include an
absolute value module, an envelope detector module, a maxi
mum value module, a divider module and a smoothing mod
ule. In accordance With some embodiments of the present
FIG. 3 is a block diagram illustration of a circuit for pro
35
FIG. 4 is a block diagram illustration of a circuit for pro
ducing arti?cial ambience in accordance With further
embodiments of the present invention;
FIG. 5 is a block diagram illustration of one possible imple
40
invention, the absolute value module may be adapted to cal
culate an absolute value signal of a mathematical representa
tion associated With the input audio signal. The envelope
detector module adapted to receive the absolute value signal
from the absolute value module and to apply a smoothing
?lter to it, giving rise to an envelope signal. The maximum
value module adapted to receive the absolute value from the
45
further embodiments of the present invention;
absolute value module and the envelope signal from said
envelope detector module and to determine the maximum of
the tWo signals at each selected time instance. The divider
50
module may be adapted to receive the envelope signal from
the envelope detector module and the maximum value signal
from the maximum value module and to calculate a ratio
betWeen the envelope signal and the maximum value signal at
each selected time instance. The smoothing module may be
adapted to receive the ratio signal from the divider module
FIG. 7 is a block diagram illustration of an exemplary
reverberation ?lter, in accordance With further embodiments
of the present invention; and.
FIG. 8 is a block diagram illustration of an exemplary
arti?cial ambience ?lter, in accordance With further embodi
ments of the present invention.
It Will be appreciated that for simplicity and clarity of
55
and to apply a smoothing ?lter, giving rise to a smoothed ratio
signal. In accordance With some embodiments of the present
invention, the smoothed ratio signal may be con?gured to
control a gain applied to the input signal to generate an output
mentation of a transient reduction module, in accordance With
some embodiments of the present invention;
FIG. 6A is a non-limiting possible implementation of a
transient reduction module for one or more input channels, in
accordance With some embodiments of the present invention;
FIG. 6B is a further implementation of a transient reduction
module for tWo or more input channels, in accordance With
illustration, elements shoWn in the ?gures have not neces sar
ily been draWn to scale. For example, the dimensions of some
of the elements may be exaggerated relative to other elements
for clarity. Further, Where considered appropriate, reference
numerals may be repeated among the ?gures to indicate cor
60
responding or analogous elements.
signal.
In accordance With further embodiments of the present
DETAILED DESCRIPTION OF SPECIFIC
EMBODIMENTS
invention, for each of the one or more channels comprising
the input audio signal, the transient reduction module may
include an absolute value module and a second maximum
value module. In accordance With some embodiments of the
present invention the absolute value modules may be adapted
65
In the folloWing detailed description, numerous speci?c
details are set forth in order to provide a thorough understand
ing of the invention. HoWever, it Will be understood by those
US 8,634,568 B2
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8
skilled in the art that the present invention may be practiced
Without these speci?c details. In other instances, Well-known
methods, procedures, components and circuits have not been
mum value module, a divider module and a smoothing mod
ule. In accordance With some embodiments of the present
invention, the absolute value module may be adapted to cal
culate an absolute value signal of a mathematical representa
described in detail so as not to obscure the present invention.
Some embodiments of the present invention relate to a
tion associated With the input audio signal. The envelope
detector module adapted to receive the absolute value signal
circuit, a method and a system for producing arti?cial ambi
from the absolute value module and to apply a smoothing
?lter to it, giving rise to an envelope signal. The maximum
value module adapted to receive the absolute value from the
ence. In accordance With some embodiments of the present
invention, there is provided a circuit for producing arti?cial
ambience. In accordance With some embodiments of the
present invention, the circuit may include a transient reduc
tion module and a reverberation ?lter. In accordance With
some embodiments of the present invention, the transient
reduction module may be adapted to reduce transients in an
input audio signal comprised of one or more channels. In
accordance With further embodiments of the present inven
tion the reverberation ?lter may be adapted to receive the
absolute value module and the envelope signal from said
envelope detector module and to determine the maximum of
the tWo signals at each selected time instance. The divider
module may be adapted to receive the envelope signal from
the envelope detector module and the maximum value signal
from the maximum value module and to calculate a ratio
betWeen the envelope signal and the maximum value signal at
each selected time instance. The smoothing module may be
adapted to receive the ratio signal from the divider module
transient-reduced signal comprised of one or more channels
and to produce a reverbed signal comprised of one or more
channels corresponding to the transient-reduced signal.
In accordance With further embodiments of the present
invention, the transient reduction module may be adapted to
affect the input audio signal in a manner to decrease the
amount of discrete echoes in the reverbed signal. In accor
dance With yet further embodiments of the present invention,
20
all other things being equal, the transient reduction module
25
invention, the smoothed ratio signal may be con?gured to
control a gain applied to the input signal to generate an output
signal.
In accordance With further embodiments of the present
include an absolute value module and a second maximum
value module. In accordance With some embodiments of the
number of taps, Without substantially increasing the presence
of discrete echoes in the reverbed signal.
each reverbed signal channel. In accordance With some
embodiments of the present invention, each of said gains may
be coupled to a reverbed signal channel and may be adapted
to amplify or to attenuate the reverbed signal channel. Each of
invention, for each of the one or more channels comprising
the input audio signal, the transient reduction module may
may be adapted to affect the input audio signal in a manner to
enable the reverberation ?lter to utiliZe a substantially smaller
In accordance With some embodiments of the present
invention, circuit may further include a gain and an adder for
and to apply a smoothing ?lter, giving rise to a smoothed ratio
signal. In accordance With some embodiments of the present
present invention the absolute value modules may be adapted
30
to calculate an absolute value of a mathematical representa
tion associated With the audio input channel With Which that
absolute value module is associated. The second maximum
value module may be adapted to determine Which of the one
or more absolute values calculated by the one or more abso
35
lute value modules is the highest. In accordance With further
the one or more adders may be connected to one of the gains
embodiments of the present invention, the envelope detector
and to one of the input signal channels and may be adapted to
sum the output of the ampli?ed or attenuated reverbed signal
channel to a corresponding input signal channel
In accordance With some embodiments of the present
invention, the transients reduction module may include a
40
module may be adapted to receive from the second maximum
value module the highest absolute value.
In accordance With further embodiments of the present
invention, there is provided a method of producing arti?cial
ambience. In accordance With some embodiments of the
present invention, the method may include receiving an input
transient detection module, a processing module and one or
more gains and/or one or more ?lters. In accordance With
audio signal comprised of one or more audio channels. Once
some embodiments of the present invention, the transient
detection module may be adapted to detect the presence of
received, transient in the input audio signal may be reduced,
45
giving rise to a transient-reduced signal comprised of one or
more channels. The transient-reduced signal may be applied
transients in an audio signal comprised of one or more chan
nels and to calculate for each detected transient a transient
to a reverberation ?lter, giving rise to a reverbed signal com
value corresponding to the acoustical properties of the tran
prised of one or more channels.
sient. In accordance With some embodiments of the present
invention the processing module may be adapted to calculate
for each transient value a corresponding gain and/or ?lter
50
value. In accordance With some embodiments of the present
In accordance With certain embodiments of the invention a
combination of a reverberation ?lter and a transient reduction
process, is used to enhance the overall ambience effect of an
invention, the one or more gains and/or one or more ?lters
input sound signal, mono, stereo, or multi-channel.
Some embodiments of the present invention may be used to
may be operatively coupled to the processing module. The
reduce the amount and/or density of synthetic re?ections,
one or more gains and/or the one or more ?lters may be 55 and/or of non-Zero ?lter taps needed for the implementation
adapted to amplify and/ or to attenuate the input audio signal
comprised of one or more channels in accordance With a gain
and/ or ?lter value received from the processing module.
In accordance With further embodiments of the present
invention, the transient reduction module and the reverbera
60
tion ?lter may be interchanged, such that the input audio
signal may be ?rst applied to the reverberation ?lter, and the
transient reduction module may be fed With the reverbed
signal thereby reducing transients in the reverbed signal.
In accordance With some embodiments of the present
invention, the transient reduction module may include an
absolute value module, an envelope detector module, a maxi
of an arti?cial reverberation ?lter, for example, a reverbera
tion ?lter as in the prior art. Further embodiments of the
present invention may be used in combination With any pres
ently knoWn or yet to be devised in the future arti?cial rever
beration ?lters. It should be noted that, in some embodiments
of the present invention, the use of arti?cial reverberation
?lter may contribute to the enhancement of sound quality. The
combination of arti?cial reverberation ?lter and a transient
reduction module may be used as an ambience ?lter With or
65
Without gain and With or Without adding the direct sound path
(or a simulation of the direct sound, such as the input signal
itself). Furthermore, some embodiments of the present inven
US 8,634,568 B2
10
tion may be used to generate arti?cial channels of audio such
as surround channels and side channels. It should be noted
that the above implementation of some embodiments of the
present invention are exemplary in nature, and that the present
invention may not be limited to any particular implementa
tion.
Further embodiments of the present invention may be used
to enhance an ambience effect in stereo or surround, by loW
accordance With some embodiments of the present invention,
by applying a transient reduction to the input signal, for
instance, a continuous steady-state input signal (such as a sine
Wave), transients are reduced from the output signal, since
When ?ltering an input having transients With any linear ?lter
(a reverberation ?lter being a private case), transients may be
maintained or reduced (for example any linear ?ltering of a
sine Wave is still a sine Wave). Thus, the output of a linear
reverberation-?lter may contain discrete echoes only if the
ering the perceived cross-correlation betWeen the channels.
One Way of lowering the perceived cross-correlation includes
introducing a large time delay betWeen the channels. When
the delay difference is very large (more than 35 milliseconds),
the human sound system is no longer able to perceive direc
input signal contains transients. Thus, in accordance With
some embodiments of the present invention, by eliminating
the transients from the input echoes may be eliminated from
the output.
Secondly, in accordance With some embodiments of the
tional information from the correlation betWeen the channels
[4, 8] and only repeated discrete echoes are heard. Some
present invention, transients may be substantially reduced
prior to being applied to the reverberation ?lter. It should be
embodiments of the present invention may be used to elimi
nate the discrete echoes, a desired effect may be achieved
not that even if the transient are only substantially reduced in
Whereby the tWo or more channels sound as if they are un
correlated.
The folloWing is a general description of the structure and
manner of operation of certain embodiments of the present
invention.
Some embodiments of the present invention may include a
reverberation ?lter. In accordance With some embodiments of
the present invention, the reverberation ?lter may be used to
20
the input and not completely eliminated, and even if the
reverberation ?lter is not linear, the reduction of level of
transients in the output may be suf?cient to cause individual
echoes to be substantially less perceivable, as can be under
stood from the perceptual effect knoWn as the HAAS effect
[8].
(and possibly ?ltered) replicas of the original sound. The
Moreover, in accordance With some embodiments of the
present invention, the reverberation ?lter may include a sub
stantially small number of non-Zero taps and/or may have an
impulse-response less dense in time. In accordance With fur
present invention may include any presently knoWn or yet to
ther embodiments of the present invention, by reducing tran
25
generate an acoustic illusion of ambience, generating delayed
be devised in the future reverberation ?lter. Exemplary imple
mentations of reverberation ?lters can be found in the prior
art. For convenience purposes replicas of the original sound
may sometime be referred to herein as ‘re?ections’. The
30
tional resources to achieve an equivalent illusion of ambience
synthetic re?ections produced by the reverberation ?lters are
intended to provide an acoustical effect Which is similar to
re?ections from Walls in an imaginary room, and in general
terms, each re?ection is a delayed, attenuated, possibly ?l
tered, replica of the sound source combination of at least one
channel of audio.
In accordance With some embodiments of the present
invention, transients in the input signal may be detected and
With still less risk of unpleasant discrete echoes. Those of
ordinary skill in the art may appreciate that by reducing the
35
40
may be reduced. In accordance With further embodiments of
the present invention, once the transients are reduced, the
audio signal may be input to a reverberation ?lter. Thus, in
accordance With some embodiments of the present invention,
the reverberation ?lter(s) may receive the input audio signal
folloWing the transients reduction. Those of ordinary skill in
the art, may appreciate that transient sound is, typically, not
essential, and in many cases not desirable, in the output of
reverberation ?lters for a Wide verity of applications. Thus, it
may be desirable to reduce transient sound prior to the appli
cation of the input audio signal to a reverberation ?lter. It is
thus advantageous to combine the reverberation process and
45
50
see [5]. For example: if the delay betWeen tWo non-Zero FIR
taps becomes greater than, say, 50 ms, and betWeen them the
impulse response is Zero, then the frequency response is a
is smaller than the bandWidth of the critical band of the human
hearing system in most audible range and is thus less notice
Having described generally the structure and manner of
operation of certain embodiments of the invention, there fol
55
loWs a more detailed description of speci?c embodiments
With reference to the draWings.
60
illustration of a circuit for producing arti?cial ambience, in
accordance With some embodiments of the present invention.
In accordance With some embodiments of the present inven
tion, a circuit for producing arti?cial ambience may include a
Reference is noW made to FIG. 3, Which is a block diagram
inbeloW. The folloWing discussions are provided for conve
nience purposes and to facilitate a better understanding of the
present invention.
the density of synthetic re?ections in the impulse-response of
the reverberation ?lter is substantially small. For example, in
that the delay betWeen the re?ections substantially large. It
Would also be appreciated by those of ordinary skill in the art
that by reducing the discrete echoes in the ?nal reverberation
effect, a reverberation ?lter Which includes feWer synthetic
re?ections may be capable of reducing the amount of per
ceived comb-?ltering, by providing to the comb-?lter’s
Z-transform a high density of Zeros (or poles) in the unit circle,
able [5].
process and a transient reduction process are discussed here
Firstly, the combination of the reverberation process and a
transient reduction process may prevent the listener from
perceiving discrete echoes in the ?ltered signal. In accor
dance With some embodiments of the present invention, the
discrete echoes may be prevented even if the number of
implemented reverberation non-Zero ?lter taps is small and/or
discrete echoes in the ?nal reverberation effect, a reverbera
tion ?lter Which includes feWer synthetic re?ections may be
capable of producing re?ections Which are characterized in
comb-?lter With dips (Z-transform Zeros) every 20 HZ, Which
a transient reduction process, as the reduction of transients
may prevent artifacts in the reverberation-?ltered audio sig
nals. Some aspects of the combination of the reverberation
sients prior to the application of the sound signal to the rever
beration ?lter, a reverberation ?lter including only
substantially small number of taps and/ or other computa
transient reduction module 110 and a reverberation ?lter 120.
In accordance With further embodiments of the present inven
tion, the reverberation ?lter 120 and the transient reduction
module 110 may be combined, for example, as folloWs: An
65
input audio signal of one or more channels may be fed into the
transient reduction module 110, the output signal from the
transient reduction module 110 comprised of one or more
US 8,634,568 B2
11
12
channels may then fed into the reverberation ?lter 120. The
and/or speci?c kinds of reverberation ?lter modules, it should
output signal from the reverberation ?lter 120 comprised of
be noted that the present invention is not limited in this
respect, and that some embodiments of the present invention
may be implemented With any presently knoWn or yet to be
devised in the future transient detection modules and/or With
any presently knoWn or yet to be devised in the future rever
beration ?lter module.
one or more channels may be fed to the ?nal output.
Turning noW to FIG. 4, there is shoWn a block diagram
illustration of a circuit for producing arti?cial ambience in
accordance With further embodiments of the present inven
tion. In accordance With further embodiments of the present
invention, a circuit for producing arti?cial ambience 200 may
Furthermore, the embodiments of the present invention
shoWn in FIGS. 3-5, and discussed hereinabove With refer
include in addition to a reverberation ?lter 220, a transient
reduction module 210, one or more output gains 230 and one
or more output adders 240. In accordance With some embodi
ence to FIGS. 3-5, are exemplary in nature. The present
invention is not limited to the con?gurations and methodol
ogy described above, and accordingly some embodiments of
the present invention may be include various modi?cations,
additions and/or subtractions. For example, in accordance
With one embodiment of the present invention, the arti?cial
ments of the preset invention, the circuit 200 shoWn in FIG. 4
may be implemented, for example, as folloWs: An input audio
signal comprised of one or more channels is fed into the
transient reduction module 210 and also each channel is fed
into a corresponding output adder 240, the output signal from
ambience circuit may include pre-processing circuitry. The
the transient reduction module 210 comprised of one or more
channels may then fed into a reverberation ?lter 220. The
pre-processing circuitry may be applied to the input signal
output signal from the reverberation ?lter 220 comprised of
one or more channels may be multiplied by a corresponding
20
output gain 230 and then fed into the corresponding output
adder. The outputs signals from all output adders may be fed
to the ?nal output.
Reference is noW made to FIG. 5, Which is a block diagram
illustration of one possible implementation of a transient
reduction module, in accordance With some embodiments of
the present invention. In accordance With some embodiments
of the present invention, the transient reduction module 310
25
the reverberation ?lter and the transient reduction module
may be interchanged. It should be noted that a circuit Whereby
the transient reduction is connected in series to the reverbera
may include a transient detection module 312 and a transient
processing module 314 and 316. In accordance With some
and/or to the input signal of the reverberation ?lter. By Way of
another exemplary embodiment, the arti?cial ambience cir
cuit may include certain post-processing circuitry. The post
processing circuitry may be applied to the audio signal before
being summed to the output adder. By Way of still another
non-limiting exemplary embodiment of the present inven
tion, various equalization ?lters may be inserted anyWhere in
the processing chain.
By Way of still another non-limiting example the order of
30
tion ?lter may not necessarily, but possibly may, produce
embodiments of the present invention, the input signal, Which
identical or optimal results but Will still have an effect Which
may be comprised of one or more audio channels, may be fed
into the transient detection module 312. The transient detec
may be, at least in some aspects, superior in comparison to
prior art solution. Those versed in the art Will readily appre
ciate that other modi?cations may be applied.
tion module 312 may be adapted to analyZe the input signal,
and may be con?gured to detect transients in the input signal.
As a result of the analysis, the transient detection module 312
may output a transient estimation signal T(t). In accordance
With some embodiments of the present invention, the tran
sient estimation module 312 may generate a speci?c transient
estimation value for every time t in the input corresponding to
the amount of transient in each input channel.
In accordance With some embodiments of the present
invention, the transient processing module 314 may be
adapted to receive T(t), at every time t, the transient (estima
tion) value, and to determine an appropriate gain or ?lter to
35
one or more input channels, in accordance With some embodi
ments of the present invention. Additionally, reference is
40
45
each channel in accordance With the transient estimation
value (for example via an analytic formula or a look-up table).
In accordance With some embodiments of the present inven
50
the greater the transient estimation value is, the loWer the
applied gain or the more attenuation is applied to certain
frequencies in the input. In accordance With some embodi
ments of the present invention the transient reduction module
some reverberation ?lter modules Which Were described
above relate to speci?c kinds of transient detection modules
one output gain 419. In accordance With some embodiments
of each input signed signal), and the output of the absolute
value module 412 may be fed into the maximum value mod
ule 414 (computing the maximum value betWeen its tWo
elements) and into the envelope detector module 415 (apply
ing a ?rst smoothing ?lter on the signal, for example a loW
pass ?lter), in parallel. The output of the envelope detector
60
frequency domain, for example, using Fourier transform. The
output of the processing module 316 and the gain or ?lter may
be fed to the output of the transient reduction module 310.
Although some of the transient detection modules and/or
accordance With further embodiments of the present inven
tion. In the embodiment of the present invention shoWn in
FIG. 6A, for the case of one channel input, the transient
reduction module may include an input terminal 402 for
receiving an input channel of an audio signal, an output ter
minal 404 for outputting one channel of audio signal, one
absolute value module 412, a maximum value module 414, an
envelope detector module 415, a divider module 416, a
of the present invention, an input audio signal may be fed into
the absolute value module 412 (computing the absolute value
may include one or more gain or ?lters and/or one or more 55
adjustable gain or ?lters. In accordance With further embodi
ments of the present invention, the transient reduction module
310 may include suitable gain(s) of ?lter(s) to provide a
variety of ampli?cation and/ or attenuation possibilities. In
accordance With some embodiments of the present invention,
in the case that a ?lter is used, the ?lter may be applied in the
made to FIG. 6B shoWing a further implementation of a
transient reduction module for tWo or more input channels, in
smoothing module 417, gain computation module 418, and
tion, the processing module 314 may be adapted to select for
each transient estimation value a gain or ?lter 316, such that
Turning noW to FIG. 6A, there is shoWn a non-limiting
possible implementation of a transient reduction module for
65
module 415 may (too) be fed into the maximum value module
414 and also fed into the nominator of the divider module 416.
The output of the maximum value module 414 may be fed
into the denominator of said divider module 416 the divider
computes the ratio betWeen the nominator and the denomi
nator. The output of the divider module 416, Which corre
sponds to the division of the output of the envelope detector
module 415 by the output of the maximum value module 414,
may be fed into the smoothing module 417 (applying a second
US 8,634,568 B2
13
14
smoothing ?lter to the output of 414, for example a loW-pass
?lter), and the output of the smoothing module 417 may be
fed into the gain computation module 418. The gain compu
function may be used. Thus, in accordance With a possible
non-limiting embodiment of the present invention, the gain
computation module may include, for example, at least a
lookup table con?gured to provide a gain value for every
tation module 418 may calculate, via a ?xed formula or look
up table (one possible example being a ‘null’ gain computa
5
tion is an identity function, another example is an addition of
input value. A simple valid non-limiting example for devising
such a look-up table is a one-to-one mapping hence table[I]:
I. Another possible mapping can be table[I]:a*I+b, Where ‘a’
a constant value so that it limits the minimum gain) a gain
factor, as described above and may instruct the gain 419 to
and ‘b’ are constants.
amplify the output of the smoothing module 417, accord
ingly. The ampli?ed signal is thus multiplied With the input
audio signal and then fed into the output.
It should be noted that in FIGS. 6A and 6B, the absolute
value, maximum value, smoothing, and divider modules cor
respond to the processing module 314 Which is included in the
transient reduction module 310 shoWn in FIG. 5. Similarly,
In FIG. 6B, there is shoWn, a block diagram illustration of
transient reduction module of an arti?cial ambience circuit in
accordance With some embodiments of the present invention,
the gain computation module With the output gain(s) shoWn in
suitable for processing an audio signal comprised of a plural
ity of channels (here tWo channels are shoWn but the present
invention is not limited in this respect). A transient reduction
module 510 suitable for processing an audio signal comprised
FIG. 5.
Note also that the transient detector Which is illustrated as
FIGS. 6A and 6B correspond to the processing module 316 in
part of the exemplary embodiment of the present invention
an output terminal 504 for outputting an audio signal includ
shoWn in FIGS. 6A and 6B does not intend to detect all the
different kinds of transients as de?ned in the terms and de?
nitions of this invention, but some sub-set of What is included
in the term as it Was de?ned. More speci?cally, the transient
detector illustrated in FIGS. 6A and 6B may be suitable for
ing multiple channels, multiple (one per-channel) absolute
detecting only transients Which manifest change in signal
of a plurality of channels in accordance With some embodi
ments of the present invention may include: an input terminal
20
502 for receiving an audio signal including multiple channels,
value modules 512, a ?rst and a second maximum value
modules 513 and 514, respectively, an envelope detector
module 515, a divider module 516, a smoothing module 517,
25
gain computation module 518, and multiple (one per-chan
nel) output gains 519. In accordance With some embodiments
of the present invention, each channel of an input audio signal
including multiple channels may be fed into one of the abso
lute value modules 512, and the output of each of the absolute
value modules 512 may be fed into the ?rst maximum value
module 513. The ?rst maximum module 513 may be adapted
30
to select the maximum value betWeen the tWo or more audio
channels. The ?rst maximum module 513 may feed the
selected maximum value signal into the second maximum
value module 514, and in parallel, feed the selected maximum
value signal into the envelope detector module 515, as Well.
The envelope detector module applies a ?rst smoothing ?lter
to the maximum value signal. The output of the envelope
detector module 515 may be fed into the second maximum
value module 514 and also fed into the nominator of the
divider module 516, and the output of the second maximum
value module 514 is fed into the denominator of the divider
module 516. The divider module 516 may compute the ratio
betWeen the nominator to the denominator, and the output of
the divider module 51 6 may be fed into the smoothing module
517. The smoothing module 517 may apply a second smooth
ing ?lter to the ratio signal, and the output of the smoothing
module 517 may be fed into the gain computation module
518. The output of the gain computation module 518 may
intensity. It should be noted, that the present invention is not
limited to the detection and/or to the reduction of any speci?c
kind of transients, rather some embodiments of the present
invention may be used to detect and/or to reduce any kind of
transients and may include any necessary presently knoWn
components and combination of components knoW in the
present or yet to be devised in the future Which are suitable for
detect and/ or for reducing transients in an audio signal. The
reduction of only a sub-set of the transients from an audio
signal to be fed into a reverberation ?lter may be su?icient to,
in some cases, to facilitate a signi?cant reduction in the per
35
40
ceived echoes in the output of the reverberation ?lter.
In accordance With some embodiments of the present
invention, the circuit for producing arti?cial ambience may
include, for example, a stereo -to stereo reverberation ?lter.
Reference is noW made to FIG. 7, Which is a block diagram
illustration of an exemplary reverberation ?lter in accordance
With further embodiments of the present invention. In accor
dance With some embodiments of the present invention, a
non-limiting possible implementation of the reverberation
?lter may be a stereo-to-stereo ?lter 710 as is shoWn in FIG.
45
7. The stereo-to-stereo reverberation ?lter may be imple
mented as folloWs: the input signal Lin is fed into a left
delay-line of M audio samples 711. The left delay-line 711
may be read at NL different delay taps TLi for a left channel
712, NL<M. The input signal Rin may be fed into a right
50
delay-line of M audio samples 713. The right delay-line 713
may be read at NR different delay taps TRj for a right channel,
multiplied using gains 519 by each of the input audio chan
NR<M 714, Where NL may or may not be set equal to NR. At
nels and then fed into the output.
In accordance With another embodiment of the present
invention, similar transient reduction modules may be used
for processing more than tWo input channels.
In accordance With one possible non-limiting embodiment
of the present invention, the envelope detector may include at
each tap i<NL, the value read at tap TLi is attenuated by a gain
GLi and fed into a left adder 715. At each tap j<NR, the value
read at tap TRj may be attenuate by a gain GRj and may be fed
into a right adder 716. The output of the left adder 715 is fed
to the left channel output of the reverberation ?lter, and the
55
output of the right adder 716 is fed to the right channel output
least a loW-pass ?lter. In accordance With a further non
limiting embodiment of the present invention, the smoothing
60
module may include at least a loW-pass ?lter. In accordance
With yet a further embodiment of the present invention, the
gain computation module may include at least a table, a
mapping or a mathematical function Which are con?gured to
provide, for every possible value received at the gain compu
tation module, a gain value ranging betWeen 0 and l . It should
be noted that any suitable table, mapping, or mathematical
of the reverberation ?lter.
It should be noted that for the embodiment of the circuit for
producing arti?cial ambience shoWn in FIG. 4, and in accor
dance With the possible implementation of the reverberation
?lter discussed in the preceding paragraph, the reduction of
transients may alloW the reverberation ?lter to require sub
65
stantially less non-Zero taps, hence a smaller NL and a smaller
NR in the example reverberation ?lter of FIG. 7. Thus, thus in
accordance With some embodiments of the present invention,
US 8,634,568 B2
15
16
it may be possible, in some cases, to reduce the numbers NL
and NR to 1, Where TL1 and TRl are large and Where the
3. The method according to claim 1, Wherein, all other
things being equal, said applying a non-linear transient reduc
direct signal is provided (at delay 0) through the direct feed of
tion affects the input audio signal in a manner to decrease the
the input channels to the output adders, as is shoWn, for
computational complexity of said applying a reverberation
?lter to the transient-reduced signal, Without substantially
increasing the presence of discrete echoes in the reverbed
example, in the exemplary reverberation ?lter illustrated by
FIG. 8, Which may be used as part of a circuit for producing
arti?cial ambience, in accordance With some embodiments of
the present invention. In FIG. 8, Which is a block diagram
illustration of a circuit for producing arti?cial ambience, in
accordance With some embodiments of the present invention.
In accordance With some embodiments of the present inven
tion, a circuit for producing arti?cial ambience may include a
transient reduction module 820 and a reverberation ?lter
signal.
4. The method according to claim 1, further comprising
amplifying and/or attenuating one or more channels of the
reverbed signal, and further comprising summing the ampli
?ed and/or attenuated reverbed signal With the input audio
signal.
5. The method according to claim 1, Wherein said applying
comprising of a combination of per-channel delays 830, per
channel gains 840, andper-channel adders 850. In accordance
a transient detection function comprises: detecting a presence
of transients in the input audio signal comprised of one or
more channels; calculating for each detected transient a tran
With further embodiments of the present invention, the rever
beration ?lter 830,840,850 and the transient reduction mod
ule 820 may be combined, for example, as folloWs: An input
audio signal of one or more channels may be fed into the
transient reduction module 820, as Well as to the per-channel
sient value corresponding to the acoustical properties of the
transient; and Wherein applying a non-linear transient reduc
tion comprises: calculating for each transient value a corre
20
adders 850, the per-channel output signals from the transient
and/or ?lter to the input audio signal.
6. The method according to claim 1, comprising:
reduction module 820 comprised of one or more channels
may then fed into the per-channel delays 830, the output
signals from the per-channel delays 830 comprised of one or
more channels may then fed into the per-channel gains 840,
the output signal from the per-channel 840 comprised of one
calculating an absolute value signal based on a mathemati
25
cal representation of the input audio signal;
smoothing the absolute value signal, giving rise to an enve
lope signal;
or more channels may then fed into the per-channel adders
850. The output signal from the channel adders 850 com
determining a maximum among the absolute value signal
and the envelope signal at each selected time instance;
prised of one or more channels may be fed to the ?nal output.
In case said reverberation ?lter is implemented digitally,
sponding gain and/or ?lter value expected to substantially
reduce the corresponding transient; and applying the gain
30
calculating a ratio signal betWeen the envelope signal and
and if the input and/ or output to said reverberation ?lter are
the maximum value signal at each selected time
analog signals, then said reverberation ?lter comprises means
for converting analog audio to digital audio at its input, and/or
smoothing the ratio signal, giving rise to a smoothed ratio
means to convert digital audio to analog audio at its output.
It Will also be understood that the system according to some
embodiments of the present invention may be a suitably pro
instance;
35
signal; and
controlling a gain applied to the input audio signal using
grammed computer hardWare. Likewise, some embodiments
the smoothed ratio signal to generate an output signal.
7. The method according to claim 6, Wherein the input
of the present invention may include a computer program
audio signal comprises tWo or more channels, and Wherein for
being readable by a computer for executing some embodi
ments of the present invention. The invention further contem
plates a machine-readable memory tangibly embodying a
program of instructions executable by the machine for
executing the method of the invention.
While certain features of the invention have been illus
trated and described herein, many modi?cations, substitu
tions, changes, and equivalents Will noW occur to those skilled
in the art. It is, therefore, to be understood that the appended
each of the tWo or more channels calculating an absolute
40
absolute value signals, and Wherein said smoothing is applied
to the overall maximum value.
45
claims are intended to cover all such modi?cations and
changes as fall Within the true spirit of the invention.
The invention claimed is:
50
1. A method, comprising:
receiving an input audio signal corresponding to sound
8. The method according to claim 1, Wherein said input
audio signal is tWo channels stereo, and Wherein the reverbed
signal is used to provide additional surround channels
intended for reproduction With said stereo input.
9. The method according to claim 2, Wherein the surround
channels provided by the reverbed signal sound as if they are
un-correlated.
10. A non-transitory computer readable medium having
computer-executable instructions for execution by a process
produced by a sound source;
applying a transient detection function for detecting a tran
sient at time t When there is a rapid change in the input
value signal based on a mathematical representation of the
respective channel from amongst said tWo or more channels
and selecting an overall maximum value from amongst the
55
ing system, the computer executable instructions for produc
ing arti?cial ambience, the computer-readable medium com
audio signal’s properties, and the transient detection
prising instructions for applying a transient detection
function further provides an estimation of an amount of
transients at time t;
function for detecting a transient at time t in an input audio
signal When there is a rapid change in the input audio signal’ s
properties, and the transient detection function further pro
applying a non-linear transient reduction to the input signal
based on the estimation of an amount of transients at 60 vides an estimation of an amount of transients at time t;
applying a non-linear transient reduction to the input signal
time t; and
applying a reverberation ?lter to the transient-reduced sig
nal giving rise-to a reverbed signal.
2. The method according to claim 1, Wherein said applying
a transient detection function and said applying a non-linear
transient reduction decrease the presence of discrete echoes
in the reverbed signal.
based on results of the transient detection function and apply
ing a reverberation simulation to the transient-reduced signal,
giving rise to a reverbed signal.
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11. The non-transitory computer readable medium accord
ing to claim 10, Wherein said instructions for applying a
non-linear transient reduction are effective for causing one or
US 8,634,568 B2
17
18
a reverberation ?lter adapted to receive the transient-re
duced signal and to produce a reverbed signal corre
more ampli?ers and/ or one or more ?lters to amplify and/or to
attenuate one or more channels of the reverbed signal, and
sponding to the transient-reduced signal.
Wherein said instructions for applying a reverberation simu
lation are further effective for summing the ampli?ed and/or
16. The circuit according to claim 15, Wherein said tran
sient reduction module is adapted to affect the input audio
attenuated reverbed signal With the input audio signal.
12. The non-transitory computer readable medium accord
ing to claim 10, further comprising instructions for: calculat
signal in a manner to decrease the amount of discrete echoes
in the reverbed signal.
17. The circuit according to claim 15, Wherein, all other
ing an absolute value signal based on a mathematical repre
things being equal, said transient reduction module is adapted
sentation of the input audio signal; smoothing the absolute
value signal, giving rise to an envelope signal; determining a
maximum among the absolute value signal and the envelope
signal at each selected time instance; calculating a ratio signal
betWeen the envelope signal and the maximum value signal at
each selected time instance; smoothing the ratio signal, giv
to affect the input audio signal in a manner to enable said
reverberation ?lter to utiliZe a substantially smaller number of
taps, Without substantially increasing the presence of discrete
echoes in the reverbed signal.
18. The circuit according to claim 15, further comprising a
gain and an adder for each reverbed signal channel, Wherein
each of said gains is coupled to a reverbed signal channel and
is adapted to amplify or to attenuate the reverbed signal chan
ing rise to a smoothed ratio signal; and controlling a gain
applied to the input audio signal using the smoothed ratio
signal to generate an output signal.
13. The non-transitory computer readable medium accord
ing to claim 10, Wherein the input audio signal comprises tWo
nel, and Wherein each of said one or more adders is connected
to one of said gains and to one of said input signal channels
and is adapted to sum the output of the ampli?ed or attenuated
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or more channels, and further comprising instructions for
calculating for each of the tWo or more channels an absolute
value signal based on a mathematical representation of the
respective channel from amongst said tWo or more channels
and instructions for selecting an overall maximum value from
amongst the absolute value signals, and Wherein instructions
to apply said smoothing to the overall maximum value.
14. The non-transitory computer readable medium accord
ing to claim 10, Wherein said input audio signal is tWo chan
nels stereo, and Wherein the reverbed signal is used to provide
additional surround channels intended for reproduction With
calculate a transient value for a transient detected at time t,
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surround channels provided by the reverbed signal sound as if
provides an estimation of an amount of transients at time
signal based on results of the transient detection func
tion; and
accordance With the respective calculated gain and/or
20. The circuit according to claim 19, Wherein the ampli
?ed and/or attenuated input audio signal is fed into said rever
beration ?lter.
21. The circuit according to claim 15, Wherein said input
audio signal is tWo channels stereo, and Wherein the reverbed
signal is used to provide additional surround channels
intended for reproduction With said stereo input.
When there is a rapid change in an input audio signal’s
properties, and the transient detection function further
t;
the transient reduction module being further adapted to
apply a non-linear transient reduction to the input audio
the transient value corresponding to the acoustical prop
erties of the transient;
calculate for the transient value at time t a corresponding
gain and/ or ?lter value; and
amplify and/ or attenuate the input audio signal at time t in
?lter value.
said stereo input.
15. A circuit, comprising:
a transient reduction module adapted to apply a transient
detection function for detecting a transient at time t
reverbed signal channel to a corresponding input signal chan
nel.
19. The circuit according to claim 15, Wherein said tran
sients reduction module is con?gured to:
22. The circuit according to claim 21, Wherein tWo or more
they are un-correlated.
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