United States Patent [191

United States Patent [191
[111
3,911,370
Pace
[451
Oct. 7, 1975
[541
[76]
AUDIO FREQUENCY AMPLITUDE
COMPENSATOR
Inventor: Jerry B. Pace, 2206 John St.,
Pasadena, Tex. 77502
[22]
Filed:
July 22, 1970
tronic Circuits) “Tone Control Circuit,” by James
Charles Soukupi.
Primary Examiner—Nathan Kaufman
Attorney, Agent, or Firm-—I-Iubbard, Thurman, Turner
& Tucker
[21] Appl. No.: 57,293
[ 57 ]
[52]
US. Cl. ............................. .. 330/21; 330/124 R
[51]
Int. Cl.2 .......................................... .. H03F 3/04
[58]
Field of Search ............................ .. 330/21, 154;
179/171 (3 A), 171 (3 B)
ABSTRACT
An audio frequency amplitude compensator is dis
closed including in a ?rst section for independently
boosting the amplitude of signals in the bass audio
range and in the treble audio range, and a second sec
tion connected in series with the ?rst section for inde
[56]
2,710,314
References Cited
pendently providing a second boost in the amplitude
UNITED STATES PATENTS
of signals in the bass audio frequency range and a sec
ond boost in the amplitude of signals in the treble
6/1955
Tongue et a1 ................. .. 330/154 X
OTHER PUBLICATIONS
Radio-Electronics-Audio-I-Iigh Fidelity, Feb. 1955
pp. 86—89, “4-Input Ampli?er,” by Albert Stratmoen.
Radio-Electronics-Audio, Vol. 23, Issue 3, Dec.
1951, pp. 27, 28 “Three-Channel Ampli?er,” by J.
audio frequency range. The ?rst section has a rela
tively narrow band bass frequency response and a rel
atively narrow band treble frequency response, and
the second section has a relatively broad bass fre
quency response and a relatively broad band treble
frequency response.
Zoucas.
Radio-Electronics, Sept. 1950, p. 76 (Radio-Elec
8 Claims, 4 Drawing Figures
,1
(-)
US. Patent
0a. 7,1975
51w 2 of2
3,911,370
JERRY 5. PACE
INVENTOR.
M
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A TTOIQIVEYQ
3,911,370
1
2
AUDIO FREQUENCY AMPLITUDE
COMPENSATOR
It is another object of this invention to provide such
a compensator which is relatively inexpensive and sim
ple to construct and which utilizes standard and easily
obtainable components.
This invention relates to sound reproduction systems
and in one of its aspects to such a system in which audio
signals in the bass and treble audio frequency ranges 5
are boosted in amplitude with respect to audio fre
quency signals in the mid-ranges.
ln sound reproduction, particularly where a broad
range of frequencies is involved, it is dif?cult to obtain
Occasionally it is desirable to cut down or attenuate
the volume at certain unwanted audio frequencies
without disturbing the relative volume at other audio
frequencies. For example, certain listeners may find the
strong bass boost generally employed in the making of
a truly flat response over the range of frequencies em
rock records to be objectionable and desire to reduce
the playback volume of the bass relative to the other
ployed. In the general range of audio frequencies in
volved in reproducing sound in the audio range, such
audio frequencies. It is thus another object of this in
vention to provide an audio frequency amplitude com
as in hi-? and stereo systems, playbackto the listener
is generally not at the same volume for frequencies in
pensator having added ?exibility so that certain un
wanted frequencies which are normally boosted in the
system can be attenuated with minimal affect on the
the lower bass range, for example 80 Hz or lower; or in
the upper treble range, for example 10 KHZ or above.
In most systems utilized for reproduction or playback
the frequency response is such that the volume of the
audio of these frequencies will be substantially less than
the volume of the audio in the mid-ranges between
these frequencies with the same setting of the volume
other audio, frequencies being played back.
These and other objects and advantages of this inven
tion are accomplished in accordance with this inven
tion by providing an audio frequency amplitude com
pensator having a ?rst bass audio frequency boost cir
control of the system.
Also, the human ear does not respond to all frequen
cuit to provide a ?rst increase of the amplitude of audio
signals in the bass frequency range, and a second bass
cies equally so that the relative intensity of sound at low
audio frequency boost circuit connected to the output
25
and high frequencies does not change at the same rate
of
said ?rst circuit to provide a second increase in the
as in the mid-range frequencies. Although the volume
amplitude of audio signals in the bass frequency range.
of the system can be adjusted to compensate for re
The audio frequency amplitude compensator may also
sponses of different ears this is not an adequate method
include a ?rst treble audio frequency boost circuit to
of compensating for the inability to respond to sound
at the low and high frequencies. Thus, the effect is that 30 provide a ?rst increase of the amplitude of audio sig
when the reproduced sound is at the proper volume in
nals in the treble frequency range, and a second treble
the mid-ranges for satisfactory listening, much of the
audio frequency boost circuit connected to the output
of said ?rst treble boost circuit to provide a second in
crease in the amplitude of audio signals in the treble
frequency range. Means is also provided for mixing the
boosted bass and treble range signals with mid-range
sound in the bass and treble ranges is reduced so much
in volume that it is either not heard, or its level is in no
way compatible with the original level at those frequen
cies when the sound was originally reproduced.
Various systems have been devised in order to boost
the volume of reproduced sound at various audio fre
quencies, particularly in the base and treble range.
However, none of these systems have provided a satis
factory boost in the desired ranges without affecting
the mid-range frequencies so that the volume during
playback closely approximates the original level of the
sound. Also, prior circuits have not provided satisfac
tory means for varying the boost independently at dif
ferent frequencies of the frequency spectrum to com
pensate for varying conditions of reproduction on play
back.
It is thus an object of this invention to provide an
audio frequency amplitude compensator providing a
boost in the amplitude of audio frequency signals in the
bass and treble ranges while having minimal effect on
the amplitude of signals in the mid-ranges.
It is another object of this invention to provide such
an compensator which provides a more accurate play
back to the listener of the original sound than previ
ously devised audio systems.
It is another object of this invention to provide such
a compensator in which the boost in amplitude in the
bass and treble ranges may be independently adjusted
and in which amplitude boost at different parts of these
ranges may be selected.
35
signals to provide a composite output signal having the
desired boost in the bass and treble audio frequency
ranges, but having little or no boost in amplitude of the
mid-range audio frequency signals.
It is preferred that each of the ?rst bass and ?rst tre
ble boost circuits have a relatively narrow band pass in
the bass and treble ranges respectively, and that each
45 of the second bass and second treble boost circuits
have a relatively broad band pass and respectively in
clude within their band widths the frequencies of said
?rst boost circuits.
A further novel aspect of this invention is the provi
sion of means for adjusting the gain of each of the boost
circuits independently of each other so that an adjust
ment is provided of the amplitude of each of the bass
and treble boost circuits. Each of the ?rst bass and tre
ble boost circuits is preferably a variable Q bandpass
55 ?lter employing an operational amplifier having a feed
back loop for adjusting the gain. The Q of the bandpass
?lter is adjusted by adjusting the gain of the operational
ampli?er.
In the drawings, wherein is illustrated a preferred em
bodiment of the invention:
FIG. 1 is a graph showing the frequency response of
the various circuits employed in this invention.
FIG. 2 is an overall block diagram of the preferred
It is another object of this invention to provide such
a compensator in which low level audio signals in the 65 form of amplitude compensator of this invention.
FIG. 3 is a schematic diagram of a preferred form of
bass and treble range which would normally be lost in
reproduction and playback may be played backvto the
the variable Q band pass ?lter which utilizes an opera
listener at an adequate and comfortable level.
tional ampli?er, and
3,911,370
3
4
FIG. 4 is a detailed schematic diagram of the pre'
ferred embodiment of the amplitude compensator of
this invention.
The audio frequency range is generally considered to
the mid-range is not affected appreciably. In this way
be that range of sound wave frequencies to which the
a more natural play back of the reproduced sound oc
curs.
The bass and treble boost which may be provided by
the preferred embodiment of this invention is illus
human ear can perceive sound, and can be from as low
trated by curve A-F in FIG. 1. Curve A illustrates a
as 10 HZ to as high as 40 KHZ. In this range of frequen
boost of about 25 db at 35 HZ, in the bass range, and
curve F illustrates a boost of about 25 db at 22 KHZ, in
cies the lower portion is generally referred to as the
bass frequency range and is considered to be below 300
HZ and generally in the range of 10 HZ to 80 HZ. The
upper range of these frequencies is generally referred
the treble range. However, in the mid-range from as
low as 100 HZ to as high as 5 KHZ the gain is no more
to as the treble frequency range and is considered to be
than about 3db, and over a large part of that range is
substantially less. Thus, the boost in the bass and treble
above 2 KHZ and generally in the range of 10 KHZ to
40 KHz. The remaining frequencies of the audio fre
quency range are considered the mid-range and they
may overlap somewhat with the upper range of bass
range frequencies and the lower range of treble range
frequencies. What range of frequencies within the
audio frequency ranges exempli?ed by curve A-F has
only minimal effect on the amplitude of the mid-range
frequencies. Curves B-G and C-H are also illustrative
of bass and treble amplitude boost provided by this in
vention as will be explained in detail.
The circuits for providing the bass and treble boost
broad ranges given which are considered to be the bass
illustrated by curve A-F are shown in FIGS. 2, 3 and 4.
or treble frequencies for a particular application de 20 Input signals in the audio frequency range are received
at an input 10 and passed through a volume or level
pends somewhat on the type of sound being repro
control RI to a buffer stage 11. Buffer 11 is illustrated
duced, the frequency response of the reproduction and
in FIG. 4 as an emitter-follower including transistor Q1
playback equipment used, and the ability of the listener
and associated components. Buffer 11 serves to match
to hear the sound when played back. Thus, for pur
poses of describing this invention the term “bass audio 25 the impedance at input 10 which is generally high to
the lower impedance of the stage that follows. The
frequency range” is employed to designate a speci?c
emitter of transistor Ql is connected to .a point 12
range of audio signals in the broad range of bass audio
which serves as an input to the various ?lter circuits to
frequencies which are to be boosted in amplitude with
be described. Connected at its input to point 12 and the
respect to signals in the mid-range of audio frequen
output of buffer 11 is a ?rst bass audio frequency boost
cies. Likewise, the term “treble audio frequency
circuit 13, illustrated as a variable Q band pass ?lter
range” is employed to designate a speci?c range of
tuned to approximately 35 HZ. Also connected to point
audio signals in the broad range of treble audio fre
12 is a ?rst treble audio frequency boost circuit 14, il
quencies which are to be boosted in amplitude with re
lustrated as a variable Q band pass ?lter tuned to ap
spect to signals in the mid-range of audio frequencies.
The speci?c range of bass and treble audio frequencies 35 proximately 22 KHZ, and a mid-range band pass circuit
15, illustrated as a band pass ?lter tuned to pass audio
to be boosted in amplitude with respect to the mid
signals from 40 Hz 20 KHz.
range frequencies will depend on the requirements of
Thus, the audio signals received at point 12 are di
the speci?c application.
vided so that only bass range signals pass through cir
In FIG. 1 a number of curves are shown illustrating
cuit 13, only the treble range signals pass through cir
the frequency response of various bass and treble am
cuit l4, and the signals in between and in the mid-range
plitude boost circuits including the amplitude compen
sator of this invention. In each of the curves shown a
pass through ?lter 15. However, signals passing
through circuits l3 and 14 are boosted in amplitude,
while the signals passing through circuit 15 are not.
45
Curve C illustrates the relative amplitude with respect
trate either a boost or attenuation of audio signals at
to the amplitude at 800 Hz of signals coming from cir
frequencies above and below this frequency. Curve K
cuit 13, and curve H illustrates the relative amplitude
illustrates the typical bass and treble boost obtained in
reference point is illustrated in the mid-range of fre
quencies and at about 800 Hz, and all the curves illus
prior audio playback systems using standard bass and
with respect to the amplitude at 800 Hz of signals com
treble tone controls. The rate of boost in such systems
is normally very slow, generally around 3 db per oc—
tave, and rises to a maximum boost of approximately
18 db at 40 HZ and 20 KHZ. However, because of the
slow rise of the boost curve K, signals in the range of
ing from circuit 14. The output of these circuits and cir
cuit 15 are connected through summing resistors Ra,
Rb, and Re respectively, to point 16 which is the input
to a second buffer 17. Buffer 17 is also an emitter
follower including transistor Q8 and its associated com
approximately 100 HZ to 5 KHZ can have a boost in am
ponents. The emitter of O8 is connected to a ?lter cir
plitude of as much as 10 db. Since most of the signal
loss in either recording or playback lies outside of this
area (i.e. below 100 HZ and above 5 KHZ) poor and
cuit 18 including a second bass audio frequency boost
circuit 18a, and a second treble audio frequency boost
unnatural reproduction of sound generally results from
circuit 18b. Filter 18a includes a bass boost adjustment
potentiometer Rd and ?lter 18b includes a treble boost
bass and treble boost of the type illustrated by curve K. 60 adjustment potentiometer Re. Filter circuit 18 also in
cludes an ampli?er 19 connected at its input to ?lters
The present invention affects a substantial improve
18a and 18b, and ampli?er 19 is in turn connected to
ment over prior bass and treble boost circuits by pro
an ampli?er-buffer 20. The circuits 18a and 18b are
viding for a bass boost beginning at a much lower fre
similar to conventional bass and treble tone control cir
quency and a treble boost beginning at a much higher
frequency. The amplitude boost provided in the low 65 cuits and, as illustrated by curves B and G, provide a
relatively broader band amplitude boost than circuits
bass range and the high treble range is of a substantially
13 and 14. Curve B illustrates the boost in amplitude
greater magnitude than that provided at other fre
obtained through ?lter 18a in the bass range audio fre
quency ranges so that the amplitude of audio signals in
h
3,911,370
5
6
quencies after suitable ampli?cation, and curve G illus
trates the boost in amplitude obtained through ?lter
18b in the treble range audio frequencies after suitable
Filter network 23a is tuned to approximately 35 Hz
and thus passes the low frequency bass signals exempli
fied by curve C in FIG. 1 to circuit 13.
ampli?cation.
Point 12 is also connected through a resistor R4 to a
unity gain for the compensator circuit from input 10 to
the output of ampli?er 20 at point 21. Curve A-F is
treble frequency bandpass ?lter network 23b compris
ing the input to the treble frequency variable Q band
pass circuit 14. Transistors Q5, Q6, and O7 in circuit 14
form an operational ampli?er 22b identical to ampli?er
thus a composite curve which illustrates the relative
22a except that the values of certain components are
Ampli?er-buffer 20 acts as an impedance match to
the output and also serves to provide approximately
changed to permit operation at the higher treble fre
quencies. Filter network 23b is tuned to approximately
amplitudes at output 21 of the bass, mid-range, and tre
ble range qudio frequencies after the input audio sig
22 KHz and thus passes the high frequency treble fre
quency signals exempli?ed by curve H in FIG. 1 to cir
cuit 14 where they are boosted in amplitude. The feed
back loop to ampli?er 22b includes a voltage divider
network Rh connected between the base of Q6 and the
nals have passed through the various ?lter circuits 13,
l4, l5 and 18. As illustrated in FIG. 1 by curve A-F, the
amplitude compensator of this invention has a rela
tively fast rise and fall time in the bass and treble
ranges, and it has substantially ?at response in the mid
ranges, when compared to prior tone control circuits
collector of Q7. The network Rh includes a variable re
sistor R5 which permits adjustment of the amount of
represented by curve K.
treble boost obtained from circuit 14. The output of
circuit 14 at point 25 is connected to point 16 through
summing resistor Rb.
As noted bass boost circuit 13 and treble boost cir
cuit 14 are variable Q bandpass ?lters. A preferred cir
cuit of such a ?lter is shown in FIG. 3 and includes an
Mid-range audio frequency signals received at point
operational ampli?er 22 having a feedback loop which
controls the gain of the ampli?er and the relative Q of
the circuit. The operational ampli?er has two inputs,
one (indicated as positive) connected to an R-C ?lter
23 tuned to the passband of the frequencies to be
boosted, and a second input (indicated as negative)
connected to the output of ampli?er 27 through a vari
able resistor Rf. Ampli?er 22 has the characteristic that
the output voltage is proportional to the difference of
the voltages applied to the input terminals. Thus, the
greater the signal which passes through ?lter 23, the
greater the output and gain in the ampli?er. The gain
25
12 are conducted through a capacitor C, to mid-range
bandpass ?lter 15 which pass from this ?lter through
resistor Re to point 16. The composite signal having the
boosted bass and treble is thus obtained at point 16, at
the base of emitter-follower Q8, and is then conducted
through Q8, and from the emitter thereof, through a ca
pacitor C2 to second bass ?lter network 18a and second
treble bass network 18b, the operation of which has
been previously described.
Curves D-I and E-.] in FIG. 1 represent situations
where one or more of the bass or treble boost circuits
have been cut off resulting in an attenuation of signals
of ampli?er 22 may be adjusted by varying Rf to vary
the voltage differential between the input terminals. It
35 in these ranges. If it is desired to reduce the gain in the
is also a characteristic of the circuit shown in FIG. 3
the bass boost circuits can be cut by reducing their gain
to zero. For example, by cutting the bass gain of bass
that when Rf is varied to vary the gain of ampli?er 22,
the Q of the ?lter network 23 is also varied. In the cir
cuits used in the preferred embodiment of this inven—
tion, and described herein, the Q has been varied from
a low value of 0.5 to high value of 2.
Curves C and H represent the bandpass characteris
playback system in the bass range, then one or both of
?lter circuit 18a off the bass frequency signals received
at the input of circuit 18 are greatly attenuated in cir
cuit 18a, or must pass through circuit 18b where the
frequency response is much higher. The resultant am
plitude in the bass range is shown in curve D. The very
tics of the FIG. 3 circuitry when employed as bass and 45 slight boost in the bass in curve D is provided by bass
boost circuit 13. However, if the gain of bass boost cir
treble variable Q bandpass ?lters, respectively. The
cuit 13 is also cut off at the same time that circuit 18a
bandpass characteristics of the input ?lter network 23
employed determine the pass band of the circuit.
FIG. 4 shows the detail schematic of the preferred
embodiment of this invention. Audio frequency signals
at point 12 are conducted through a resistor R2 to a
bass frequency bandpass ?lter network 23a comprising
the input to the bass frequency variable Q bandpass cir‘
is cut off, so that bass audio frequency signals received
at 12 must pass through either treble circuit 14 or the
mid-range bandpass ?lter 15, then the relative ampli
tude of the bass audio frequency signals is represented
by curve E. In curve E no boost is present at all in the
bass range signals.
If it is desired to cut or attenuate treble range audio
cuit 13. Transistors Q2, Q3 and Q, in circuit 13 form an
frequency signals, then one or both of the treble band
operational ampli?er 22a with the base of Q2 con 55 pass circuits 14 or 18b can be cut by reducing their gain
nected to ?lter network 23a to form one input, and the
control to zero. Curve I represents the relative ampli~ r
base of Q3 forming the second input. The base of O3 is
connected to a feedback loop including a voltage di
vider network Rg connected between the output of am
pli?er 22a at point 24 (the collector of Q4) and the base
of 03. This voltage divider network includes a variable
tude of treble range signals with bandpass circuit 18b
cut, and curve J represents the relative amplitude of
treble range signals with bandpass circuit 18b and boost
resistor R3 which permits adjustment of the amount of
bass, treble, and mid-range audio frequency signals can
circuit 14 cut.
Thus, it can be seen that the relative amplitude of the
bass boost obtained from circuit 14. Point 24 is con
be easily adjusted in the compensator circuit of this in
nected through a summing resistor Ra to point 16. 65 vention between the extremes represented by the
curves E-.! and A-F. The compensator of this invention
Thus, bass range audio signals are conducted to ampli
is well adapted for use in many different audio systems
?er 22a where they are boosted and the boosted base
to provide desired variations in the amplitude of the
signals are present at point 16.
3,911,370
7
8
bass and treble audio frequency signals with little or no
effect on the amplitude of the mid-range audio signals.
From the foregoing it will be seen that this invention
is one well adapted to attain all of the ends and objects
hereinabove set forth, together with other advantages
the mid-range audio frequencies are not appreciably
boosted in amplitude.
2. The compensator of claim 1 including means for
adjusting the gain of at least one of said ?rst and second
circuits.
3. The compensator of claim 1 wherein each of said
which are obvious and which are inherent to the appa
ratus.
It will be understood that certain features and sub
combinations are of utility and may be employed with
variable Q band pass ?lters is an operational feedback
ampli?er having a variable Q control means connected
between the output and an input of said operating am
reference to other features and subcombinations. This 10
pli?er.
is contemplated by and is within the scope of the
4. An audio frequency compensator for increasing
the amplitude of bass and treble range audio signals
with respect to the amplitude of mid-range audio sig
nals‘, comprising in combination: an input; a ?rst bass
audio frequency boost circuit connected to said input
and providing for a ?rst increase in the amplitude of
signals at said input in the bass audio frequency range;
claims.
As many possible embodiments may be made of the
invention without departing from the scope thereof, it
is to be understood that all matter herein set forth or
shown in the accompanying drawings is to be inter
preted as illustrative and not in a limiting sense.
What is claimed is:
1. An audio frequency amplitude compensator re
a ?rst treble boost circuit connected to said input and
providing for a ?rst increase in the amplitude of signals
at said input in the treble audio frequency range; mix
ing means connected to the outputs of each of said ?rst
sponding to audio frequency signals including such sig
nals in the mid-range audio frequency range and in the
bass and treble audio frequency ranges to provide an
increase in the amplitude of said bass and treble range
circuits for providing a ?rst composite signal including
signals in relation to the amplitude of mid-range audio
frequency signals, comprising in combination: an input
for receipt of said audio frequency signals; an output;
25
said boosted bass and treble audio frequency signals; a
second bass audio frequency boost connected to said
mixing means for receipt of said composite signal to
provide for a further increase in the amplitude in the
bass audio frequency range thereof; a second treble
audio frequency boost circuit connected to said mixing
a ?rst bass audio frequency boost circuit including a
variable Q band pass ?lter having a relatively narrow
band pass frequency response in the bass audio fre
quency range, and connected to said input and provid
means for receipt of said composite signal to provide
amplitude of said bass audio frequency signals, said
ond composite signal having increased amplitudes in
for a further increase in the amplitude in the treble
ing for a ?rst increase in the amplitude of said bass
audio frequency range thereof, one of each of said bass
audio frequency signals, a ?rst treble audio frequency
boost circuits and one of each of said treble boost cir
boost circuit including a variable Q band pass ?lter
cuits having a relatively broad band pass, and the other
having a relatively narrow band pass frequency re
sponse in the treble audio frequency range and con 35 of said bass boost circuits having a relatively narrow
band pass within the band pass of said one bass boost
nected to said input to provide a ?rst increase in the
circuit,
and the other of said treble boost circuits hav
amplitude of said treble audio frequency signals; a sec
ing a relatively narrow band pass within the band pass
ond bass audio frequency boost circuit connected be
of said one treble boost circuit, and means connected
tween said ?rst bass audio frequency boost circuit and
to the outputs of said second circuits to provide a sec
said output and providing for a second increase in the
the bass and treble ranges with respect to the amplitude
second bass audio frequency boost circuit having a rel—
of bass and treble range signals at said input.
atively broad band pass frequency response and includ
5. The compensator of claim 4 further including a,
ing within its band widths the band width of said ?rst
bass audio frequency boost circuit; and a second treble 45 bandpass ?lter for passing audio frequency signals be
tween said bass and treble ranges, said band pass ?lter
audio frequency boost circuit connected between said
connected between said input and said mixing means.
?rst treble audio frequency boost circuit and said out
6. The compensator of claim 4 wherein each of said
put and providing for a second increase in the ampli
?rst bass and treble boost circuits are variable Q band
tude of said treble audio frequency signals, said second
pass ?lters.
treble audio frequency boost circuit having a relatively
7. The compensator of claim 4 further including
broad band treble frequency response and including
means for adjusting the amplitude gain of each of said
within its band width the band width of said ?rst treble
?rst circuits.
audio frequency boost circuit, the composite band pass
8. The compensator of claim 7 further including
of said ?rst and second bass and treble boost circuits
being such that said audio frequency signals in the bass 55 means for adjusting the amplitude gain of each of said
second circuits.
and treble audio frequency ranges can be boosted sub
stantially in amplitude while audio frequency signals in
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