Automatic graphic equalizer
United States Patent [191
A [11]
Patent Number:
4,688,258
[45]
Date of Patent:
Aug. 18, 1987
Kunugi et al.
[54] AUTOMATIC GRAPHIC EQUALIZER
OTHER PUBLICATIONS
[75] Inventors: Yoshiro Kunugi; Shinichi Suzuki;
Masayuki Kato, all of Saitama, Japan
[73] Assignee:
Pioneer Electronic Corporation,
Tokyo, Japan
[21] Appl. No.: 793,384
[22] Filed:
[30]
circuitry for measuring the effect of the physical envi
Japan .............................. .. 59-229990
....
[51]
Int. cu
[52]
us. c1. .................................. .. 381/103; 381/102;
[58]
Field of Search ............... .. 381/103, 107, 59, 115,
. . . . . . . . . . . ..
110412 3/04
381/107
381/111; 324/77 E, 78 R
References Cited
9/1965
1/1973
Bore .................................. .. 381/107
Willett
...................... .. 324/78 F
3,732,370 5/1973 Sacks
4,045,731 8/1977 Tokunou
324/78 F
4,340,780
7/1982
Odlen ...... ..
381/103
4,458,362
7/1984
Berkovitz ..
381/103
4,610,024
9/1986
Schulhof ........................... .. 381/103
FOREIGN PATENT DOCUMENTS
58-138200
8/1983
Japan ................................. .. 381/103
59-230315 12/1984 Japan
2068678 8/1981 United Kingdom ............ .1. 381/103
PINK NOIS
f‘I 5
ALC
MICROPHONE
-
AMF‘.
.7
13»
CONT.
FREQ, DIVIDER
FREQ-DIVIISING RATIO
com. SIG.
ronment receiving a sound on the frequency character
istics of the sound, and for adjusting the characteristics
of a graphic equalizer to compensate for distortions in
the desired ?at frequency response caused by the physi
cal environment. The circuitry includes a pink noise
generator supplying pink noise to the graphic equalizer
during an initialization operation, the graphic equalizer
being controlled by a controller to present a ?at fre
quency characteristic. The equalizer output is sent to a
speaker which supplies the pink noise as a sound signal
to the selected environment. A microphone picks up the
U.S. PATENT DOCUMENTS
3,207,848
3,708,746
ABSTRACT
An automatic graphic equalizer for a sound system has
Foreign Application Priority Data
[56]
Electronic Product Design, vol. 1, No. 3, Jun. 1980, p. 31.
Primary Examiner—-Gene Z. Rubinson
Attorney, Agent, or Firm-Sughrue, Mion, Zinn,
Macpeak, and Seas
[57]
Oct. 31, 1985
Oct. 31, 1984 [JP]
"Simple Spectrum Analyser Covers Four Octaves,”
sound in the selected environment and converts it to an
electrical signal which is supplied through an ALC
ampli?er to a frequency-variable band-pass ?lter to
detect the signal level in each of the equalizer frequency
bands. The level signals are smoothed in a level detector
and digitized to be input to the controller which read
justs the graphic equalizer to compensate for distortions
in the desired ?at frequency response caused by the
selected environment.
5 Claims, 4 Drawing Figures
U. S. Patent Aug. 18,1987
Sheetl of3
FIG. 7
\ PRIOR ART
3
PINK NOISE
GEN.
4
GRAPHIC
EQ.
9
VARlABLE
RESISTOR
4,688,258
U. S. Patent Aug. 18,1987
Sheet2 of3
NP
4,688,258
U. S. Patent Aug. 18,1987
Sheet3 of3
4,688,258
FIG. 3
R5
RZQ
R1
33
11
OUT
1
4,688,258
2
through the respective BPFs. The controller 13 then
AUTOMATIC GRAPHIC EQUALIZER
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automatic graphic
equalizer and particularly to an automatic graphic
equalizer in which the frequency characteristics of
sound, produced by a pink noise source, and introduced
into and returned from a predetermined physical envi
controls the graphic equalizer 4 so as to have frequency
characteristics which compensate for the detected fre
quency characteristics which produce a non-?at fre
quency spectrum. Accordingly, the sound inside the car
appears to have a ?at frequency characteristic.
In such a conventional device, however, to detect the
respective pink noise levels in the various frequency
bands, a plurality of BPFs are necessary in order for the
ronment, are measured and the measurement used to
level of pink noise in each of the graphic equalizer’s
automatically control the frequency characteristics of
several frequency bands to be detected. Therefore, as
the number of the frequency bands is increased, it be
the graphic equalizer.
2. Description of the Prior Art
A conventional automatic graphic equalizer is shown
in FIG. 1. In FIG. 1, an adder 2 is provided at an audio
signal input terminal 1 so as to add pink noise received
from a pink noise generator 3 to an audio signal re
ceived through the terminal 1. The output of the adder
2 is applied to a graphic equalizer 4 in which the fre
quency characteristics of the adder output are con
trolled. The output from the graphic equalizer 4 is ap
plied to a speaker 6 through an ampli?er 5. The speaker
converts the electrical input to the speaker into sound
which is emitted into a predetermined physical area, for
example, the inside of a car.
The emitted sound is reflected from the car interior
and received together with the re?ected sound by a
microphone 7. The microphone is connected to a BPF
(band-pass ?lter) circuit 10 for detecting the frequency
characteristics of microphone received sound, through
a microphone ampli?er 8 and a variable resistor 9. The
BPF circuit 10 is constructed of a plurality of BPFs
each having a different pass band, the number of BPFs
corresponding to the number of adjusting frequency
bands of the graphic equalizer 4. The outputs of the
respective BPFs are alternatively selected through a
comes necessary to correspondingly increase the num
ber of the BPFs and the number of contacts in the
switch 11. This makes for a complicated arrangement.
Further, because the average pink noise level applied to
a group of BPFs changes depending on the apparatus
mounting position and/or the conditions inside the car,
it is necessary to make the average level of the pink
noise some predetermined value before measuring the
frequency characteristics. Therefore, the variable resis
tor 9 is required which further complicates the device.
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate the
above-mentioned disadvantages in the conventional
automatic graphic equalizer.
It is another object of the present invention to pro
vide an automatic graphic equalizer having a simpli?ed
arrangement.
The present invention is applied to an automatic
graphic equalizer arranged such that a pink noise signal
is applied to an audio signal line. The pink noise is
passed through a graphic equalizer and then applied to
a speaker which introduces the pink noise as sound into
switch 11. Each selected output is converted into a
a predetermined physical environment. The sound in
digital signal by an A/D (analog-to-digital) converter
12 and applied as an input to controller 13 which may be 40 the physical environment is detected by a microphone.
a programmed microcomputer.
The level of the detected sound in every one of a plural
A predetermined program operates the controller 13
ity of frequency bands is determined, and the frequency
to produce controller outputs which control the
characteristics of the graphic equalizer are controlled in
graphic equalizer 4, the variable resistor 9, and the
response to the respective detected levels. The auto
switch 11 so as to automatically obtain a ?at environ 45
matic graphic equalizer of the invention includes a fre
ment frequency characteristic in the selected physical
quency-variable BPF in which the center frequency of
environment.
the
passband can be changed by controlling circuit
Such an arrangement operates in the following man
parameters. This frequency-variable BPF is used as the
ner. To initialize the equalizer circuit, the audio signal
means for detecting the signal levels in the respective
input terminal 1 is earthed, the pink noise generator 3 is
frequency bands of the sound detected by the micro
energized to supply pink noise to the graphic equalizer
phone.
4, and the graphic equalizer 4 is operated to produce a
?at frequency characteristic. The equalized pink noise
produced from the equalizer 4 is ampli?ed by the ampli
The frequency-variable BPF may be a so-called SCF
(switched capacitor ?lter). The signal detected by the
?er 5 and emitted into the physical environment, such as
a car interior, through the speaker 6. The emitted sound
is detected by the microphone 7 together with the
sound re?ected inside the car, ampli?ed by the micro
microphone is supplied to the SCF through a micro
phone ampli?er having an ALC (automatic level con
phone ampli?er 8, and then applied to the variable resis
tor 9. The variable resistor 9, controlled by controller
13, is used for making the average level of signals ap
BRIEF DESCRIPTION OF THE DRAWINGS
plied to the A/D converter 12 a predetermined refer
trol) function.
FIG. 1 is a block diagram showing a conventional
automatic graphic equalizer;
FIG. 2 is a block diagram showing an embodiment of
the automatic graphic equalizer according to the pres
The controller 13 receives the output of the A/D
converter 12 which represents the frequency character 65 ent invention; and
FIGS. 3 and 4 are circuit diagrams of portions of the
istics of the sound from the selected physical environ
switched capacitor ?lter shown in block form of in
ment and detects these frequency characteristics from
the amplitude level of the pink noise which passes
FIG. 2.
ence level.
3
4,688,258
4
DETAILED DESCRIPTION OF PREFERRED
EMBODIMENT
the detected signal level may be applied directly to the
A/D converter 12 without smoothing, the sampling
frequency is necessarily increased requiring a more
A preferred embodiment of the present invention will
complicated circuit.
The data indicating the detected signal level in each
frequency band so obtained is analyzed by the control
ler 13, and then the graphic equalizer 4 is adjusted on
the basis of this analysis so that a ?at frequency charac
now be described with reference to FIGS. 2-4.
FIG. 2 is a block diagram showing an embodiment of
automatic equalizer according to the present invention.
The portions of FIG. 2 which are the same as those in
FIG. 1 are identi?ed with common reference numerals.
Only the parts different from those shown in FIG. 1 will
teristic can be obtained over all frequency bands.
FIGS. 3 and 4 are circuit diagrams each showing a
be described hereinafter. Sound inside a car is detected
portion of the circuit of SCF 17, which is a so-called
by microphone 7, and set to a predetermined level by an
f-variable (frequency-variable) type ?lter. FIGS. 3 and
ALC microphone ampli?er 15. The output from ampli
4 are circuit diagrams of an LPF and an HPF, respec
?er 15 is supplied to a combination circuit comprised of
example, of an LPF (low-pass ?lter) and an I-IPF (high
pass ?lter), the frequency characteristics of the respec
tively, in which only the frequency f can be changed
with the Q (sharpness) kept substantially constant by
suitably changing variable resistor elements Rz-Rg
(FIG. 3) and variable resistor elements R8, R9, and R12
tive ?lters being controlled, respectively, by the output
(FIG. 4).
of a programmable frequency divider 20 and the output
of a frequency divider 21, the frequency divider 21
operational ampli?ers 31-33, capacitors C1 and C2, and
frequency dividing the output of the programmable
resistors R1-R6. In the LPF, the cut-off frequency ft is
frequency divider 20.
l/(C1C2R3R4) and Q is R2/R3. In this case, R5 is se
lected to be equal to R6. FIG. 4 shows an example of the
a BPF l6 and an SCF 17. The SCF 17 is comprised, for
5
FIG. 3 shows an example of the LPF comprised of
The BPF 16 is a ?lter which has a ?xed frequency
characteristic for allowing signals within a frequency
HPF comprised of operational ampli?ers 41-43, capaci
pass-band which cannot be covered by the SCF 17 to 25 tors C3 and C4, and resistors R7—R12. In this HPF, the
pass through. Of course, the BPF 16 is unnecessary if
cut-off frequency fc is l/(C3C4R9R11) and Q is R3/R12.
the frequency pass-band can be covered by the SCF 17.
In this case, R10 is made equal to R1].
The respective outputs of the ?lters 16 and 17 are
Accordingly, if the LPF and HPF are connected in
selected by a switch 18 and applied to a level detector
series and the respective values of fc are suitably set, it is
19. The signal levels detected by the detector 19 are 30 possible to provide a BPF, the center frequency of
which is controllable. If the variable resistors R2-R4
and the variable resistors R3, R9, and R12 in the LPF
and HPF respectively, are comprised of the so-called
I‘ supplied to an A/D converter 12.
The balance of the arrangement is the same as that in
FIG. 1 except that the output of the graphic equalizer 4
is applied to the ampli?er 5 through a fader circuit 14.
The automatic graphic equalizer is initialized as fol
lows. The audio signal input terminal 1 is earthed and
35
the pink noise generator 3 is energized to apply the pink
noise to the graphic equalizer 4. The graphic equalizer
switched capacitors (SC), the SCF can be realized.
According to the present invention, for example, an
SCF in which the center-frequency of the passband can
be easily controlled by changing circuit parameters is
used for detecting respective frequencies. In this way
multiple band pass ?lters and a complex switching cir
is controlled to have a ?at frequency characteristic. The
setting of the initial conditions is automatically per 40 cuit can be eliminated from the automatic graphic
formed by a controller 13. Thereafter, the pink noise is
equalizer.
emitted into the inside of a de?ned physical environ
If a device having the ALC function is used as a
ment such as a car through a speaker 6, and the emitted
sound and the re?ected sound are detected by the mi
microphone ampli?er, the arrangement can be further
crophone 7. Although the signal detected by the micro
phine is controlled by the ALC microphone amplifer 15
simpli?ed because it becomes unnecessary to use a com
45
plicated variable resistor arrangement responsive to the
controller 13 output.
so that the average output level of the signal becomes a
What is claimed is:
predetermined value, the frequency characteristics of
1. An automatic graphic equalizer comprising:
pink noise generating means;
means for producing pink noise from said pink noise
the output signal, which are affected by the conditions
inside the car, will nevertheless be detected by the SCF
17.
For the SCF 17 to detect the frequency characteris
generating means on an audio signal line;
graphic equalizer means connected to said audio sig
tics over the signal’s entire frequency band, the frequen
cy-dividing ratio of the programmable frequency di
nal line for adjusting the frequency characteristics
of received signals;
vider 20 is controlled by a frequency-dividing ratio
means for converting the output from said graphic
control signal supplied to the programmable frequency
equalizer means into a sound signal and for intro
divider 20 from the controller 13, so that the pass-band
characteristics of the SCF 7 (i.e. the center frequency of
environment;
the passband) is varied. Therefore, the center frequency
of the SCF 17 is sequentially made to coincide with to 60
each of the frequency bands of the graphic equalizer 4.
The signal levels in each frequency band to which the
ducing said sound signal into a selected physical
sound detecting means for detecting sound in said
selected physical environment; and
SCF is set is detected and applied to the controller 13 in
control means for detecting the respective levels of
the signals detected by said sound detecting means
in a plurality of frequency bands and for control
the form of a digital signal by the operation of the A/D
ling the frequency characteristics of said graphic
converter 12. A level detector 19 is provided to detect 65
the average signal level from the SCF and to rectify and
smooth the detected signal, so as to reduce the required
equalizer on the basis of the respective detected
sampling frequency of the A/D converter 12. Although
levels;
said control means including a frequency-variable
band-pass ?lter for detecting the respective signal
5
4,688,258
6
low-pass ?lter being taken from the output of said
levels in said plurality of frequency bands, the cen
ter frequency of the pass-band of said band-pass
second operational ampli?er;
?lter being changeable by controlling ?lter circuit
said high-pass ?lter comprising a fourth operational
ampli?er (41) having a variable feedback resistor in
parallel with a feedback capacitor, one input
parameters; wherein said sound detecting means
comprises a microphone and an automatic level
control ampli?er for amplifying the output of said
thereto receiving the signal input to said high-pass
microphone.
?lter, the output of said fourth operational ampli
2. An automatic graphic equalizer according to claim
1, in which said frequency-variable band-pass ?lter is a
switched capacitor ?lter.
3. An automatic graphic equalizer according to claim
2, in which said switched capacitor ?lter is comprised of
?er being connected to one input of a ?fth opera
a high-pass ?lter and a low-pass ?lter, said center fre
quency of the pass~band being changeable in response to
15
a varying frequency clock signal.
4. An automatic graphic equalizer comprising:
pink noise generating means;
tional ampli?er (42) having a feedback resistor
through a series resistance (R10), the output of said
?fth operational ampli?er being connected to one
input of a sixth operational ampli?er (43) having a
feedback capacitor through a third variable resis
tance (R12), the output of said sixth operational
ampli?er being connected to said one input of said
fourth operational ampli?er through a fourth vari
able resistance (R9).
5. An automatic graphic equalizer comprising:
pink noise generating means;
means for producing pink noise from said pink noise
generating means on an audio signal line;
graphic equalizer means connected to said audio sig
means for producing pink noise from said pink noise
nal line for adjusting the frequency characteristics
of received signals;
means for converting the output from said graphic
generating means on an audio signal line;
graphic equalizer means connected to said audio sig
equalizer means into a sound signal and for intro
ducing said sound signal into a selected physical 25
environment;
nal line for adjusting the frequency characteristics
of received signals;
means for converting the output from said graphic
equalizer means into a sound signal and for intro
ducing said sound signal into a selected physical
sound detecting means for detecting sound in said
selected physical environment; and
environment;
control means for detecting the respective levels of
the signals detected by said sound detecting means
in a plurality of frequency bands and for control
sound detecting means for detecting sound in said
selected physical environment; and
control means for detecting the respective levels of
the signals detected by said sound detecting means
in a plurality of frequency bands and for control
ling the frequency characteristics of said graphic
equalizer on the basis of the respective detected
ling the frequency characteristics of said graphic
levels;
equalizer on the basis of the respective detected
said,control means including a frequency-variable
band-pass ?lter for detecting the respective signal
levels;
levels in said plurality of frequency bands, the cen
said control means including a frequency-variable
ter frequency of the pass-band of said band-pass
band-pass ?lter for detecting the respective signal
?lter being changeable by controlling ?lter ciruit
levels in said plurality of frequency bands, the cen
ter frequency of the pass-band of said band-pass
parameters;
wherein said frequency-variable band-pass ?lter is
comprised of a series connected low-pass ?lter and
?lter being changeable by controlling ?lter circuit
parameters;
high-pass ?lter;
said low-pass ?lter comprising a ?rst operational
ampli?er (31) having a variable feedback resistor in
parallel with a feedback capacitor, the output of
said ?rst operational ampli?er being connected to
one input of a second operational ampli?er (32)
wherein said control means further includes a level
45
detector for smoothing the output of said frequen
cy-variable band-pass ?lter, an analog-to-digital
converter receiving the output from said level de
tector and controller means responsive to the digi
tal output from said converter for controlling the
frequency characteristics of said graphic equalizer
having a feedback capacitor through a ?rst vari
able resistance (R4), the output of said second oper
ational ampli?er being connected to one input of a
in response to the levels detected by the frequency
variable band-pass ?lter;
third operational ampli?er (33) having a feedback
resistor, the output of the third operational ampli
said equalizer further including a band-pass ?lter
arranged to receive the same signals received by
said frequency-variable band-pass ?lter and switch
means for selectively connecting either the band
?er being connected to one input of said ?rst opera
tional ampli?er through a second variable resis
tance (R3), the one input of said ?rst operational
pass ?lter or frequency-variable band-pass ?lter to
said level detector.
ampli?er being adapted to receive the signal input
to said low-pass ?lter with the output from said
,
60
65
t
i
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