Automatic sound level compensator for a sound reproduction device

Automatic sound level compensator for a sound reproduction device
United States Patent [191
[11] Patent Number:
Takagi et al.
[45]
[54]
4,815,142
3/1989 lrnreh ................................ .. 381/106
COMPENSATOR FOR A SOUND
REPRODUCTION DEVICE MOUNTED IN A
4,823,392
4,864,246
4/ 1989 Walker ........ ..
9/ 1989 Kato et al. ........................ .. 381/107
FOREIGN PATENT DOCUMENTS
[7 5] Inventors: Kazunori Takagi; Shinichi Sato;
Masahiko Ito; Hideo Yamamoto, all
of Saitama, Japan
[73] Assignee: Pioneer Electronic Corporation,
Tokyo, Japan
[21] App1.No.: 552,364
[22] Filed:
Foreign Application Priority Data
Japan ................................ .. 63-23563
Japan ................................ .. 63-23959
[51]
Int. 01.5 ............................................. .. H04B 1/00
[52]
US. Cl. ................................. .. 381/86; 381/98;
381/103; 381/57
Field of Search ................. .. 381/102, 98, ,86, 103,
381/57
[56]
References Cited
U.S. PATENT DOCUMENTS
1,938,256
2,069,853
2,577,893
3,182,271
4,179,669
4,641,344
12/1933
2/1937
12/1951
5/1965
12/1979
2/1987
4,648,117
3/1987
Kunungi et al. .................... .. 381/86
4,710,962 12/1987
Matsui ............................... .. 381/102
LIN
c
.
.
.
.
.
.
Japan ................................... .. 381/86
OTHER PUBLICATIONS
Continuation of Ser. No. 263,768, Oct. 28, 1988, aban
Feb. 3, 1988 [JP].
Feb. 5, 1988 [JP]
8/1984 Austria .
223164782 l/ 1974 Fed. Rep. of Germany
2250725B2 4/1974 Fed. Rep. of Germany
2415816B2 9/1975 Fed. Rep. of Germany
2641675A1 3/ 1978 Fed. Rep. of Germany
3321225Al 12/ 1983 Fed. Rep. of Germany
0130613TI 9/1985 Fed. Rep. of Germany
60-261298 12/1985
doned.
[58]
375006
Jul. 11, 1990
Related US. Application Data
[30]
May 21, 1991
AUTOMATIC SOUND LEVEL
VEHICLE
[63]
Date of Patent:
5,018,205
Jacobs ............................... .. 381/102
European Search Report, #P38 37 538.9-Apr. 20, 1989.
Magazine Article-“Phone Technik,” Frankfurter
Fachverlag, 1984 Author-Peter Zastrow.
Primary Examiner-Forester W. Isen
Attorney, Agent, or Firm-Sughrue, Mion, Zinn,
Macpeak & Seas
[57]
ABSTRACT
In an automatic loudness compensator provided in a
sound reproduction device in a vehicle, the sound level
is compensated to reproduce a sound source with the
high ?delity intended by the producer of the source of
sound. The level of sound frequency-pressure is in
creased or decreased relative to a middle range of sound
frequency at a sound level lower or higher than a refer
ence sound level, respectively. The level of sound fre
quency-pressure is also'adjusted based on the noise
produced by the movement of the vehicle and on the
acoustic characteristic of the passenger compartment of .
the vehicle.
I 7 Claims, 9 Drawing Sheets
US. Patent
May 21, 1991
Sheet 1 of 9
5,018,205
FIG. 7
10
TAPE
PLAYER
1
2
/
/
'
coma _]
I1k
13
/15
AcousTIc
18a
SOUND
TRANS-
PRE-
LEVEL
MISSON
POWER
AMPLIFIER
CONTROL
SPACE
AMPLIFIER
TION CKT
POWER
m
DISK
/
COMPENSA-
PLAYER
18
V b
L_—’ AMPLIFIER
11
POWER
AMPLIFIER
"PF
CI9
{18c
/20
IN
<>
’
ADOER
‘
'
BAND
PASS
FILTERI
‘
421
1
BAN)
ELIMINATION,,.
FILTER
/22
_ our ' * IN:
’.
'
21'
MIDDLE RAIIEEI
" LOGARITHHIC
’ COMPRESSION
‘AMPLIFIER
OUT
. H23
ouqcIN
'c?'TER
(H‘GH 8' Low RANGE’
‘
US. Patent
May 21, 1991
Sheet 3 of 9
FIG. 5
5,018,205
FIG. 6
BE5230
INPUT [dB]
INPUT [ dB 1
H5. 7
+2OdB
ourpur LEVEL OF THE
REFERENCE EOUAL- SENSATION
CURVE
+10 dB__
3.1d B
~.52.30
-30 dB
~L0dB
100
1K
2K
10K
FREQUENCY [HZ]
FIG. ' 8
0m2sw38za
.EmGuz>w3.n_ma
0
l u Lr
MOVEMENT NOISE COMPENSATION REFERENCE CURVE
LIDLING NOISE COMPENSATION REFERENCE CURVE
1K
-
FREQUENCY [Hz 1
10K
U.S. Patent
May 21, 1991
Sheet 4 019
5,018,205
FIG. 9
M
%
.1015
MEFEREME EQUAL-SENSATlON CURVE
LPS[ROEdUVBNRDL]E
MA
MA
50
100
200
1K
2lK
10IK
V
FREQUENCY [Hz]
FIG. 70
2o
‘
Y 26
24
0E
A r‘
i32%‘
2b
(23b
is;
,25b
US. Patent
-
May 21, 1991
Sheet 7 of 9
5,018,205
US. Patent
May 21, 1991
FIG. 27
LIN Cr
HPF
Rm F
HPF
FIG. 23
BPF
LPF
HPF
115D
Sheet 8 of 9
5,018,205
1
5,018,205
2
nal and the slider is gradually decreased so that the
diagrammatic curve of the sound frequency-pressure
characteristic is made gradually flatter as shown in
AUTOMATIC SOUND LEVEL COMPENSATOR
FOR A SOUND REPRODUCTION DEVICE
'
FIG. 17. Although the second conventional loudness
MOUNTED IN A VEHICLE
compensator is similar to the ?rst one in these respects,
the diagrammatic curve of the sound frequency-pres
sure characteristic has a larger slope due to the reso
nance circuit 2 and is shorter in the entire range of
FIELD OF THE INVENTION
sound frequency, as shown in FIG. 18. When the sliders
The presentinvention relates to an automatic loud 10 d and d’ of the sound level controlling variable resistors
VR] and VR1' of the third conventional loudness com
nesscompensator, particularly to an automatic loudness
pensator are slid toward the signal input terminals a and
compensator for a sound reproduction device mounted
a’ of the resistors so that the sound levels are height
in a vehicle.
This is a Continuation of Application No. 07/263,768
?led Oct. 28, 1988 now abandoned.
ened, the slider g of the second controlling variable
resistor VRZ which is operated in conjunction with the
BACKGROUND OF THE INVENTION
FIG. 13 shows a ?rst conventional loudness compen
preceding variable resistors is slid to the terminal f of
the resistor VRz so that the level of the output from the
resonance circuit 2 is gradually lowered as shown in
FIG. 19. In the fourth conventional loudness compensa
sator disclosed in Japanese Patent Application (OPI)
No. 24861 1/86 (the term “OPI” as used herein means an
“unexamined published application”). The compensator
comprises a sound-level-controlling tapped variable
20 tor, the frequency range component output from the
?lter 4 is linear to the audio input signal, and the fre
quency range component output from the other ?lter 5
is logarithmically compressed and then added to the
output from the preceding ?lter, so that the diagram
resistor VR1 and a CR ?lter circuit 1. A high-frequency
sound range compensation capacitor C1 is connected
between the intermediate tap c and signal input terminal
of the variable resistor VR1. A low-frequency sound
range compensation capacitor C2 and a resistor R1 are
connected in series with each other between the inter
mediate tap c and other terminal b of the variable resis
tor VR1 and connected in parallel with a low-frequency
25 matic curve of the sound frequency-pressure character
istic is made gradually ?atter as shown in FIG. 20.
The drawback of the ?rst and the second conven
’ tional loudness compensators including the sound level
sound range compensation level-limiting resistor R2.
controlling tapped variable resistors is that the sound
FIG. 14 shows a second‘ conventional loudness com 30 frequency-pressure characteristic is such that the level
pensator disclosed in Japanese Patent Application
(OPI) No. 223909/83. The compensator has a sound
levelcontrolling tapped variable resistor VR1. A reso
nance circuit 2 is connected between the intermediate
35
tap c and terminal b of the variable resistor VR1.
FIG. 15 shows a third conventional loudness com
pensator disclosed in Japanese Patent Application
(0P1) No. 223909/83. The compensator has a pair of
sound-level-controlling variable resistors VRi and VR|’
for two channels, and a third controlling variable resis 40
tor VRZ. which is operated in conjunction with the
preceding variable resistors. The level of the output
from a resonance circuit 2 is regulated by the third
controlling variable resistor VR2. The compensator
of sound pressure is heightened by an equal quantity in
the lower and the higher ranges of sound frequency
relative to that of the sound pressure in the middle
range of sound frequency as shown in FIG. 17, when
the sound level is not higher than a value corresponding
to the position of the tap of the variable resistor (that
position is usually at an angle of 120' in the case where
the maximum rotative angle of the variable resistor is
300°). Particularly in the ?rst conventional loudness
compensator having the CR ?lter circuit 1, the slope of
the diagrammatic curve of the sound frequency-pres
sure characteristic is 6 dB/oct and there is a pressure
level ?uctuation in the frequency range of 200 Hz or
more so that the compensator has the particular disad
also has addition circuits 3 and 3’ differentially con 45 vantage that the sound compensated through the com
pensator is unclear or the middle-frequency sound
nected to the outputs of the sound-level-controlli'ng
through the compensator is weak.
variable resistors VR] and VR1.
As for the third conventional loudness compensator
FIG. 16 shows a fourth conventional loudness com
having the second controlling variable resistor VRZ. the
pensator disclosed in Japanese Utility Model Applica
quantity of the increase in the loudness in the low-fre
tion (OPI) No. 95723/ 85. The compensator comprises a
quency sound and/or the high-frequency sound can be
plurality of ?lters 4 and 5 for dividing an audio input
signal into two or more frequency range components, a
gradually changed for adjustment by the second con
logarithmic compression ampli?er 6 which logarithmi
trolling variable resistor. For that reason, the compen
sator does not have the above-mentioned drawback and
cally compresses at least one of the outputs from the‘
?lters, and an addition circuit 8 which adds the output 55 disadvantage. However, a drawback is that the compen
sator needs three or four mutually-coupled variable
from the ampli?er 6 to the other ?lter output processed
resistors, so that the spatial ef?ciency thereof is lower
by a flat ampli?er 7.
and the rotation thereof does not feel good.
When the slider d of the sound-level-controlling vari
As for the fourth conventional loudness compensa
able resistor VRl of the ?rst conventional loudness
compensator-x is slid toward the intermediate. tap 0 60 tor, the diagrammatic curve of the sound frequency
pressure characteristic is similar to an equal-sensation
thereof ‘between the signal input terminal a and the tap
c, the sound frequency-pressure characteristic is such
curve’ (which is a Fletcher-Manson equal-loudness
that the level of sound pressure is heightened by an
curve) at a low sound level. For that reason, a draw
back is that the quantity of compensation by the com
equal‘ quantity in both a low and a high range of sound
frequency. When the slider d is slid between the signal 65 pensator is excessive for listening to the reproduced
input terminal a and the tap c in such a manner that the
sound from a music source on the market or from the
resistance between the tap and the slider is gradually
increased, the resistance between the signal input termi
In the process of production of the music source on the
like, and the quality of the sound is therefore unnatural.
3
5,018,205
market, sounds are usually subjected to multiple-track
4
on the noise produced by a moving vehicle equipped
with a sound reproduction device provided with the
loudness compensator.
recording through multiple microphones, quality ad
justed by an effect producing device or the like. and
mixed-down into a two-channel stereo format. At that
time, a person listens to the recorded sounds at a certain
level through a monitoring reproduction device in a
studio. The sound level is usually as high as about 100
above-mentioned drawbacks and disadvantages of the
phons. The customer purchases the music source to
listen to the sounds through his sound reproduction
device. If the customer listens to the sounds at nearly
conventional loudness compensators.
Accordingly, the present invention provides an auto
matic loudness compensator for a sound reproduction
the same sound level as the other person listens to them
device mounted in a vehicle, wherein the compensator
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate the
through the monitoring reproduction device in the stu
performs optimal compensation in terms of sound level
dio, the customer obtains nearly the same acoustic qual
to reproduce the sounds of a sound source with the high
ity as the other person does, under ideal conditions (in
?delity intended by the producer of the source of sound.
reality, the acoustic quality depends on the sound level 15 In the compensator, a compensation circuit is provided
characteristics of the ears, the acoustic characteristics of
so that a quantity of compensation, which is nearly
the room and the properties of the sound reproduction
equal to the difference between a reference equal-sensa
device). Although the loudness of the reproduced
tion curve at a prescribed sound level and each of other
equal-sensation curves at other sound levels, is set by
sounds is usually much lower than 100 phons, the sound
level is higher than 100 phons in some cases and is, for
the compensation circuit to automatically compensate
example, 120 phons.
the sound frequency-pressure characteristics at the
FIG. 3 shows Robinson-Datson curves which are
equal-sensation curves at the sound levels of pure
sounds. It is understood from FIG. 3 that the form of
the Robinson-Datson curve at the sound level of 100
phons is different from that of the curve at the sound
level of 120 phons. In other words, the rise in the level
other sound levels. Another quantity of compensation is
also set by the compensation circuit against masking
based on the noises produced in moving the vehicle at
the time of movement thereof. The level of sound pres
sure in a low or high range of sound frequency is in
creased relative to.that of sound pressure in a middle
range of sound frequency at a sound level lower than
of sound pressure in a low range of frequency or the fall
in the sensitivity of the ear to the level of sound pressure
the prescribed sound level, and is lowered relative to
that of sound pressure in the middle range of sound
frequency at a sound level higher than the prescribed
sound level. The level of sound pressure in the low and
the high ranges of sound frequency can thus be changed
in the range is relatively steep at the sound level of 100
phons but relatively low at the sound level of 120 phons.
This means that the quality of a sound reproduced at a
high sound level is not equal to that of the sound moni
tored by a person at the time'of recording of the sound.
In other words, the level of the pressure of the repro
along the reference equal-sensation curve correspond
ing to the prescribed sound level, to always obtain the
same natural quality of sound at the mutually different
duced sound in a low range of sound frequency or a
high range of sound frequency feels higher at the high
sound level. Therefore, the quality of the reproduced
levels of sound, even in the passenger compartment of
sound at the high sound level is different from that of
the vehicle, with the high ?delity intended by the pro
the reproduced sound at a low level.
ducer of the source of sound.
It is another object of the present invention to pro
vide an automatic loudness compensator for a sound
sation curve at the reference sound level of 100 phons
reproduction device mounted in a vehicle. The com
and the other equal-sensation curves at other levels. It is
pensator performs optimal compensation in terms of
understood from FIG. 4 that the level of sound pressure
rises or the sensitivity of the ear thereto falls in the 45 sound level to reproduce the sounds of a sound source
with the high fidelity intended by the producer of the
low-frequency sound range of 200 Hz and less and the
FIG. 4 shows the differences between the equal-sen
sound source. In the compensator, a sound level con
middle-frequency and high-frequency sound ranges
trolling variable resistor having an intermediate tap is
from 1.5 kHz to 10 kHz as the sound level falls, and that
provided so that the sound frequency-pressure charac
the level of sound pressure falls or the sensitivity of the
ear thereto rises in the sound ranges as the sound level 50 teristic is automatically compensated in terms of a
sound level controlled by the variable resistor. In the
rises. For that reason, the differences need tobe com
automatic loudness compensator, a compensation cir
pensated if the quality of the reproduced sound is to be
cuit is provided so that the level of sound pressure in a
nearly equal to that of the sound monitored by the per
son at the time of the recording of the sound,
Each of the conventional loudness compensators
.
low range of sound frequency and/or a high range of
sound frequency is increased relative to that of sound
including the sound level controlling tapped variable
pressure in a middle range of sound frequency at a
sound level lower than a reference level, and is lowered
relative to that of sound pressure in the middle range of
sound frequency-pressure characteristic is made flat
sound frequency at a sound level higher than the refer
when the variable resistor is set for the highest sound
level. For that reason, a drawback of the compensators 60 ence level. As a result, the same natural quality of sound
resistors function so that the diagrammatic curve of the
is that the compensation becomes ineffective when lis
is obtained at the mutually different levels of sound,
tening to the sounds of the music source on the market
or to the like, at a high sound level which makes the
even in the passenger compartment of the vehicle, with
tion at a sound level higher than that of the reference
equal-sensation curve or compensate for masking based
FIG. 1 shows a block diagram of a sound reproduc
tion device mounted in a vehicle and equipped with an
the high fidelity intended by the producer of the source
quality of the sounds unnatural.
of sound.
All of the four conventional loudness compensators 65
BRIEF DESCRIPTION OF THE DRAWINGS
have drawbacks in that they do not perform compensa
5,018,205
5
6
automatic loudness compensator which is an embodi
sure to provide a desired acoustic transmission charac
ment of the present invention;
teristic. The output from the acoustic transmission
space compensation circuit 15 is supplied to power
FIG. 2 shows a block diagram of an automatic loud
ness compensator:
'
'
FIG. 3 shows Robinson-Datson equal-loudness,
curves which are equal-sensation curves:
FIG. 4 shows graphs of the differences between a
reference equal-sensation curve and the other equal-sen
ampli?ers 18a, 18b and 180 corresponding to loudspeak
ers 16a, 16b and 160, respectively, which are disposed in
prescribed positions in the passenger compartment 17a
of the vehicle 17. Since the loudspeaker 160 is for
sounds of very low frequency a low-pass ?lter (LPF) 19
is'connected between the acoustic transmission space
FIG. 5 shows the input-output characteristic of the l0 compensation circuit 15 and the power ampli?er 18c.
logarithmic compression ampli?er of the automatic
FIG. 2 shows the automatic loudness compensator
which is a part of the sound level control circuit 14. The
loudness compensator shown in FIG. 2:
FIG. 6 shows the input-output characteristic of the
audio input signal to the compensator is supplied to the
band pass ?lter 20 and band elimination ?lter 21. The
limiter circuit of the automatic loudness compensator
shown in FIG. 2:
15 band pass ?lter 20 allows the middle-frequency sound
FIG. 7 shows sound frequency-pressure characteris
range component of the'signal to pass through and the
band elimination ?lter 21 (including two resonance
tics compensated by the automatic loudness compensa
sation curves;
I
tor in terms of sound level but not of masking:
circuits); allows the low-frequency and high-frequency
FIG. 8 shows noise compensation curves at the sound
sound range components of the signal to pass through
level for the reference equal-sensation curve to indicate 20 and then be ampli?ed. The center frequency f1, repro
the difference in the level of sound pressure between the
ductionllevel A1 and reproduction frequency band Af]
noise compensation curves;
FIG. 9 shows sound frequency-pressure characteris
I the band eliminantion ?lter 21 and the center frequency
of the low-frequency sound range resonance circuit of
tics compensated by the ‘automatic loudness compensa
f2, reproduction level A; and reproduction frequency
tor in terms of both sound level and masking; '
FIGS. 10, 11 and 12 show block diagrams of auto
band Afz 2 of the high-frequency sound range resonance
matic loudness compensators which are other embodi¢
lows: 2O<f1§ 100 (Hz). 2<f2§ 10 (kHz). A1§A2,
Af1§200 (Hz) and Afzél (kl-I2). The low-frequency
ments of the present invention:
.
circuit of the band elimination ?lter are preset as fol
FIGS. 13, 14, 15 and 16 show diagrams of conven
and the high-frequency sound range components ex
30 tracted and ampli?ed by the band elimination ?lter 21
tional loudness compensators:
are logarithmically compressed by a logarithmic com
FIGS. 17, 18, 19 and 20 show sound frequency-pres
sure characteristics compensated by the conventional
pression ampli?er 22 and then subjected to output limi
loudness compensators, respectively:
tation above a voltage by a limiter circuit 23 for a de
sired sound level. The low-frequency and the high-fre
loudness compensator which is yet another embodiment 35 quency sound range components processed through the
of the present invention:
limiter circuit 23 are added, by an adder 24, to the mid
dle-frequency sound range component extracted by the
FIGS. 22A and 22B showrsound frequency-pressure
characteristics compensated by the automatic compen
band pass ?lter 20 so that an audio output signal is out
sator shown in FIG. 21;
put from the adder.
FIG. 21 shows a circuit diagram of an automatic
FIG. 23 shows a circuit diagram of an automatic
loudness compensator which is yet another embodiment
of the present invention;
FIG. 24 shows a circuit diagram of an automatic
As mentioned above. FIG. 4 shows the differences
between ‘the reference equal-sensation curve shown in
FIG. 3 corresponding to a sound level of 100 phons and
other equal-sensation curves shown therein and corre
loudness compensator which is yet another embodiment
sponding to other sound levels. The differences need to
45 be compensated if sounds of the same quality as those
of the present invention; and
FIG. 25 shows sound frequency-pressure characteris
which are heard by a person listening through a monitor
tics compensated by the automatic loudness compensa
when the sounds are being recorded are to be repro
tor shown in FIG. 24.
duced. For compensation of the differences, the band
pass ?lter 20 for extracting the middle-frequency sound
DETAILED DESCRIPTION OF THE
50 range component is provided. The band pass ?lter 20 is
PREFERRED EMBODIMENTS
needed for the purpose of compensating the differences
Embodiments of the present invention are hereafter
between the reference equal-sensation curve and the
described in detail with reference to the drawings at
other equal-sensation curves at a sound level of less than
tached hereto. The same symbols in the drawings de
100 phons. Also, the band pass ?lter 20 compensates the
note mutually corresponding portions.
differences between the reference equal-sensation curve
FIG. 1 shows a block diagram of a sound reproduc
and the other equal-sensation curves at sound levels of
tion device mounted in a vehicle and equipped with an
more than 100 phons to obtain a sound frequency-pres
automatic loudness compensator which is one of the
sure characteristic so that the level of sound pressure in
embodiments. A tape player 10 or compact disk player
a low and a high range of sound frequency is lowered
11 reproduces a‘ sound by sending out a reproduced
relative to that of sound pressure in a middle range of
audio signal and supplies it to a preampli?er 13 through
sound frequency.
a switch 12. The preampli?er processes the signal and
The low-frequency and the high-frequency sound
produces an output 'which is subjected to loudness con
range components extracted and ampli?ed to desired
trol by a sound level control circuit 14 and then sub
frequency characteristics by the band elimination ?lter
jected to acoustic transmission space compensation. 65 21 are logarithmically compressed by the logarithmic
Acoustic transmission space compensation circuit 15
compression ampli?er 22 so that the levels of the com
cooperates with the loudness compensation circuit in
ponents are set relative to that of the middle-frequency
setting a sound level as a reference level of sound pres
sound range component. Shown by a one-dot chain line
7
5,018,205
in FIG. Sis the linear input-output characteristic of the
logarithmic compression ampli?er 22 for the middle
8
sound frequency, another one of which is for the low
range of sound frequency and yet another one of which
in FIG. 5 is the other linear input-output characteristic
is for the high range of sound frequency. In this embodi
ment, the levels of the outputs from logarithmic ampli?
of the ampli?er 22 for the low-frequency and the high
ers 22a and 22b and those of the outputs from limiter
frequency sound range component. Shown by a full line
frequency sound range components. The diagrammatic
circuits 23a and 23b can be optionally set. Reference
numeral 26 shown in FIG. 10 is a ?at ampli?er.
line of the latter characteristic of the ampli?er 22 has a
Because of the small diameter of each loudspeaker of
smaller slope than that of the former characteristic
the sound reproduction device, sounds of very low
thereof. For that reason, the ratio of the middle-fre
quency sound range component to the low-frequency O frequency are likely to be ampli?ed by the low-fre
quency sound range resonance circuit of the band elimi
and the high—frequency sound range components can be
nation ?lter 21 of the automatic loudness compensator
gradually changed by the logarithmic compression am
pli?er 22.
'
shown in FIG. 2, below the lowest resonance frequency
f0 of the loudspeaker, so that harm is done to the device.
The limiter circuit 23 is provided to damp the low
In order to prevent this harm, a high-pass ?lter 27 may
frequency and the high-frequency sound range compo
nents at a sound level of more than 100 phons. FIG. 6
be connected‘ to the input side of the band elimination
shows the input-output characteristic of the limiter
?lter 21, as shown in FIG. 11, to damp a frequency
circuit 23. A point a shown in FIG. 6 corresponds to the
range of sounds harmful to the proper operation of the
sound level for the reference equal-sensation curve. The
sound reproduction device.
input levels of the high-frequency and the low-fre 20
quency sound range components, which are higher than
the point a, are limited by the limiter circuit 23 as shown
in FIG. 6.
FIG. 12 shows an automatic loudness compensator
which is yet another embodiment and is for a two-chan
nel sound reproduction device mounted in a vehicle.
One compensation line of the compensator is jointly
used for the low-frequency sound range components of
FIG. 7 shows desired sound frequency-pressure char
acteristics achieved by‘ the action of the above 25 audio input signals in a right and a left channel, while
the other compensation lines of the compensator are
described sections of the automatic loudness compensa
tor.
used for the other components of the audio input signals
The equal-sensation curve of both the sounds repro
respectively. The low-frequency sound range compo
nents processed by the former compensation line are
duced by the sound reproduction device and the noise
produced in moving the vehicle 17 differs from the
added, by adders 28R and 28L for mixing, to the other
equal-sensation curve of pure sounds. Since masking is
components processed by the latter compensation lines.
This results in simplifying the circuit con?guration of
caused on the sound reproduction device by the noise
the automatic loudness compensator. Limiter circuits
produced in moving the vehicle, the masking also needs
to be compensated. Although the level of the movement
23b may or may not be provided in this embodiment.
noise and the level of the sound source need to be com 35
FIG. 21 shows an automatic sound compensator
pared with each other if the masking is to be accurately
which is yet another embodiment and is for a sound
compensated, the masking is compensated in terms of
reproduction device mounted in a vehicle. Shown as
the difference between the sound pressure level of about
Rin, Lin, Rout and Lout in FIG. 21 are an input termi
45 dB (A) when an ordinary passenger car is idle the
nal for a right channel, an input terminal for a left chan
sound pressure level of about 70 dB (A) when the car is 40 nel, an output terminal for the right channel and an
travelling 100 km/hr in this embodiment. FIG. 8 shows
the difference in the sound pressure level between an
output terminal for the left channel, respectively.
Stereo-channel signals supplied to the input terminals
idling noise compensation reference curve shown by a
Rin and Lin are entered into high-pass ?lters 111 and
one-dot- chain line in the drawing and corresponding to
111', respectively, and into the two input terminals of an
the sound level of the above-mentioned reference equal 45 adder 114. The middle-frequency and high-frequency
sensation curve and a 100 km/hr movement noise com
sound range components of the stereo-channel signals
pensation reference curve shown by a full line in the
are extracted by the high-pass ?lters 111 and 111’ and
drawing and corresponding to the reference equal-sen
supplied to the input terminals a and a’ of sound level
sation curve. This sound level difference is additionally
controlling variable resistors 113 and 113’ through level
preset as a masking compensation quantity in the auto
control resistors 112 and 112’, respectively. The sliders
matic loudness compensator shown in FIG. 2. The
cl of the variable resistors 113 and 113’ are operated in
masking compensation quantity is limited within
conjunction with each other. The adder 114 adds the
hatched regions shown in FIG. 9 indicating the loud
stereo-channel signals to each other. The output from
the adder 114 is supplied to a band pass ?lter 115 for
ness compensation characteristics, to compensate for
the masking caused by the noise produced in moving
the vehicle 17, to produce a high quality of reproduced
sounds with the high ?delity intended by the producer
extracting the low-frequency'sound range component
of the output of the adder. The low-frequency sound
range component is supplied to the intermediate taps of
of the source of sound.
the sound level controlling variable resistors 113 and
Although the frequency band of the audio input sig
113' through level control resistors 116 and 116', respec
nal is divided into two sections, one of which is for the 60 tively. Sound level compensated signals are sent out
middle range of sound frequency and the other of
from the output terminals Lout and Rout connected to
which is for the low and the high ranges of sound fre
the sliders d of the sound level controlling variable
resistors 113 and 113', respectively.
quency in the above-described embodiment, the present
invention is not con?ned thereto but may be otherwise
The gradient and cutoff frequency fc1of the high-pass
embodied so that a low-pass ?lter 25a and a high-pass 65 ?lters 111 and 111' are 12 dB/oct, and about 300 Hz to
?lter 25b are provided, as shown in FIG. 10, to divide
about 500 Hz, respectively. The adder 114 combines the
the frequency band of an audio input signal into three
stereo-channel signals to form a single signal. The gradi
sections, one of which is used for the middle range of
ent and cutoff frequency fczi of the band pass ?lter 115
5,018,205
10
respectively. The gradient of the band pass ?lter 115
pass ?lters 111 and 111' and that of the output from the
band pass ?lter 115 are dropped to produce the sound
may be — l8 dB/oct., — 6 dB/oct. or the like, but should
preferably be — l2 dB/oct. or less to make passenger
frequency-pressure characteristic shown by a one-dot
chain line b in FIG. 22B and similar to the preceding
_ are ~12 dB/oct. and about 70 Hz to about 150 Hz.
compartment acoustic transmission space compensation
effective.
sound frequency-pressure characteristics a and c. The
concave portion of each of the diagrammatic curves of
the sound frequency-pressure characteristics a, b and c,
If the sound reproduction device equipped with the
automatic loudness compensator shown in FIG. 21 has
which is made by the actions of the high-pass ?lters 111
box-shaped bass loudspeakers of small diameter, the
amplitude of the vibration of the loudspeakers of small
diameter, the amplitude of’ the vibration of the loud
and 111', and the band pass ?lter 115 around the fre
quency of 250 Hz, nearly corresponds to the convex
portion (peak) of the diagrammatic curve of the acous
tic characteristic of the passenger compartment of the
vehicle, which arises around the frequency of 250 Hz.
speakers is greatly increased below the resonance fre
quency of the ports thereof. The low band cutoff fre
quency fc22 of the band pass ?lter 115 effectively pre
vents an abnormal sound from being caused due to the
Therefore, the concave portion of each of the diagram
matic curves of the sound frequency-pressure charac
great increase in amplitude of vibration of the loud
teristics a, b and c effectively serves to compensate the
speakers or prevents an abnormal sound such as chatter
acoustic characteristic of the passenger compartment of
the vehicle.
If it is unlikely that an abnormal sound will be caused
speaker is embedded. The cutoff frequency fc22 and 20 in the very low range of sound frequency, the band pass
gradient of the band pass ?lter 115 are determined de- _ ?lter 115 may be replaced with a low-pass ?lter.
and distortion from being caused by the loudspeaker in
the very low range of sound frequency when the loud
pending on the properties of the loudspeakers, to be 50
Hz and 12 dB/oct., respectively, in this embodiment.
Sound frequency-pressure characteristics corre
sponding to the mutually different portions of the slid
ers d of the sound level controlling variable resistors
Although the frequency band of each of the stereo
channel signals is divided into two sections and the
low-frequency sound range components of the signals
25 are added to each other to make a single signal to damp
113 and 113' are now described with reference to
harmful very-low-frequency sound components in the
embodiment shown in FIG. 21, the present invention is
graphs shown in FIGS. 22A and 22B. When the sliders
not con?ned thereto but may be otherwise embodied so
d are located on the intermediate taps c of the variable
that the low-frequency sound range components of the
signals are separately processed for the right and the left
resistors 113 and 113’, the sound frequency-pressure
characteristic shown in FIG. 22A is'produced. The
levels 11 of sound pressure in the low range of sound
frequency and 12 of sound pressure in the middle and
channels as shown in FIG. 23, to produce the same
sound frequency-pressure characteristics as those
shown in FIGS. 22A and 228.
high ranges of sound frequency are determined by the
resistances of the level control resistors 112. 112', 116
and 116'. The frequency range (between fc1 and fc21) of
the concave portion (which is made by the high-pass
?lters 1.11 and 111’ and theband pass ?lter 115) of the
diagrammatic curve of the sound frequency-pressure
characteristic shown in FIG. 22A and the level 13 of
ponents of the stereo-channel signals are damped at a
sound level above a reference sound level in the em
bodiment shown in FIG. 21, the present invention is not
con?ned thereto but may be otherwise embodied so that
a construction as shown in FIG. 24 is provided to damp
Although only the low-frequency sound range com
both the low-frequency sound range components and
the high-frequency sound range components of stereo
sound pressure are determined to nearly correspond to
the convex portion (peak) of the diagrammatic curve of
the acoustic characteristic of the passenger compart
ment of the vehicle. A full line 0 in FIG. 22B shows the
channel signals at a high sound level above a reference
sound level. In the embodiment shown in FIG. 24, a
low-pass ?lter 115a and a high-pass ?lter 115b are pro
sound frequency-pressure characteristic produced 45 vided so that the ?lter 115a extracts the low-frequency
when the sliders d of the variable resistors 113 and 113
sound range component of the input signal and the
' are located on the intermediate taps thereof. When the
other ?lter 11511 extracts the high-frequency sound
sliders d are slid and located on the input terminals a of
range component of the input signal. These components
the variable resistors 113 and 113'. the sound frequency
are supplied to the intermediate tap of a sound level
pressure characteristic shown by dotted line a in FIG.
50
controlling variable resistor 113 through level control
22B is produced. When the sliders d are slid from the
intermediate d taps to the input terminals a, the levels of
resistors 116a and 116b. The low band cutoff frequency
of a band pass ?lter 121 and the cutoff frequency of the
the middle-frequency and the high-frequency sound
low-pass filter 1150 may be equalize to the cutoff fre
range components sent out from the high-pass ?lters
quency of the high-pass ?lter 111 and the high band
111 and 111’. are increased because the resistance be! 55 cutoff frequency of the band pass ?lter 115, respec
tween the slider and the input terminal is gradually
decreased, but the level of the low-frequency sound
tively. The high band cutoff frequency of the band pass
?lter 115 and the cutoff frequency of the high-pass ?lter
range component sent out from the band pass ?lter 115
115b are made suf?ciently different from each other and
is not increased because the resistance between the
set at values which produce sound frequency-pressure
slider and the intermediate tap is gradually increased. 60 characteristics, the diagrammatic curves of which have
For that reason, the sound frequency-pressure charac
concave portions around the frequency of 1.5 kHz as
teristic shown by the full line 0 is gradually changed
shown in FIG. 25. A full line 0 in FIG. 25 shows the
toward the characteristic shown by the dotted line a.
sound frequency-pressure characteristic produced
When the sliders d are slid from the intermediate taps c
when the slider d of a sound level controlling variable
to the grounded terminals b of the variable resistors 113 65 resistor 113 is located on the intermediate tap c thereof.
and 113', the resistance between the slider and the inter
A dotted line a in FIG. 25 shows the sound frequency
mediate tap is increased but the resistance ratio is not
pressure characteristic produced when the slider d is
changed, so that the levels of the outputs from the high
located on the input terminal a of the variable resistor
11
5,018,205
113. A one-dot chain line b in FIG. 25 shows the sound
frequency-pressure characteristic produced when the
slider d is located between the tap c and the grounded
terminal b of the variable resistor 113. As for the em
12
2. A sound reproduction device including an auto
matic loudness compensator for compensating a sound
level of an audio signal, comprising:
means for increasing a ?rst level of sound pressure of
bodiment shown in FIG. 24, the audio sensation is effec
said audio signal in a ?rst range of sound frequency
tively compensated at a high sound level and the acous
tic characteristic of the passenger compartment of a
vehicle is also compensated around the 1.5 kHz fre
quency convex portion of the diagrammatic curve.
In each of the above-described embodiments shown
in FIGS. 21, 23 and 24, the sound level controlling
tapped variable resistors and the ?lters are provided in
combination to divide each of the right and the left
relative to a second level of sound pressure in a
stereo-channel signals into different frequency bands of
middle range of sound frequency when a sound
level of said audio signal is lower than a reference
sound level; and
means for decreasing said ?rst level of sound pressure
relative to said second level of sound pressure in
said middle range of sound frequency when said
sound level of said audio signal is higher than said
reference sound level;
wherein said sound reproduction device is mounted
components and the cutoff frequencies of the ?lters are
in a vehicle; and
made suf?ciently different from each other to make the
further comprising: means for adjusting said ?rst
concave portion in each of the diagrammatic curves of
level of sound pressure relative to said second level
the sound frequency-pressure characteristics. The fre
of sound pressure based on an acoustic characteris
quency range of the concave portion is nearly equal to 20
tic of a passenger compartment of said vehicle.
that of the convex portion (which is made due to the
3. A sound reproduction device including an auto
re?ection or absorption of the sounds between the loud
matic loudness compensator for compensating a sound
speaker and the person listening in the passenger com
level of an audio signal, comprising:
partment of the vehicle) of the diagrammatic curve of
means for increasing a ?rst level of sound pressure of
the acoustic characteristic of the acoustic transmission 25
said audio signal in a ?rst range of sound frequency
space of the passenger compartment. The levels of the
relative to a second level of sound pressure in a
outputs from the ?lters are set by the level control
middle range of sound frequency when a sound
resistors to obtain frequency characteristics to compen
level of said audio signal is lower than a reference
sate the sounds in terms of the acoustic transmission
sound level;
space of the passenger compartment as well. The
means for decreasing said ?rst level of sound pressure
sounds are thus compensated in terms of not only the
relative to said second level of sound pressure in
sound level but also the acoustic characteristic of the
said middle range of sound frequency when said
sound level of said audio signal is higher than said
passenger compartment of the vehicle. This results in
making the quality of the sounds natural.
reference sound level;
?rst ?lter means for extracting a middle-frequency
In the above-described embodiments shown in FIGS.
sound range component from said audio signal;
21 and 23, the damping property in the low range of
second ?lter means for extracting a low-frequency
sound frequency or in the low and the high ranges of
and a high-frequency sound range component from
sound frequency at a high sound level prevents the clip
said audio signal;
sound of an ampli?er, the tensile or abnormal action
means for logarithmically compressing the output of
sound of the loudspeaker the chatter noise of the trim in
said second ?lter means;
the passenger compartment of the vehicle or the like,
means for limiting the level of the output of said
which would be harmful.
logarithmic compressing means; and
The present invention is not con?ned to the above
means
for adding the output of said level limiting
described embodiments, but may be embodied or prac
means to the output of said ?rst ?lter.
ticed in other various ways without departing from the 45
4. An automatic loudness compensator as in claim 3,
spirit or essential character thereof.
further comprising:
What is claimed is:
a high-pass ?lter having an input connected to said
1. A sound reproduction device including an auto
input audio signal and an output connected to the
matic loudness compensator for compensating a sound
input of said second ?lter means.
level of an audio signal, comprising;
5. A sound reproduction device including an auto
means for increasing a ?rst level of sound pressure of
matic loudness compensator for compensating a sound
said audio signal in a ?rst range of sound frequency
level of an audio signal, comprising:
relative to a second level of sound pressure in a
means for increasing a ?rst level of sound pressure of
middle range of sound frequency when a sound 55
said audio signal in a ?rst range of sound frequency
level of said audio signal is lower than a reference
relative to a second level of sound pressure in a
sound level; and
middle range of sound frequency when a sound
means for decreasing said ?rst level of sound pressure
level of said audio signal is lower than a reference
relative to said second level of sound pressure in
sound level;
said middle range of sound frequency when said
means for decreasing said ?rst level of sound pressure
sound level of said audio signal is higher than said
relative to said second level of sound pressure in
reference sound level;
said middle range of sound frequency when said
wherein said sound reproduction device is mounted
sound level of said audio signal is higher than said
in a vehicle; and
reference sound level;
further comprising: means for adjusting said ?rst
?rst ?lter means for extracting a middle-frequency
level of sound pressure relative to said second level
sound range component from said audio signal;
of sound pressure based on a noise produced by
second ?lter means for extracting a low-frequency
movement of said vehicle.
sound ‘range component from said audio signal;
5,018,205
-
14
13
third ?lter means for extracting a high-frequency
fourth ?lter means for extracting a high-frequency
sound range component from said audio signal;
?rst logarithmic compression means for logarithmi
cally compressing the output of said second filter
sound range component from said audio signal in
said second channel;
?fth ?lter means for extracting a low-frequency
sound range component from a combined input
means;
signal comprising said audio signals in said ?rst and
second logarithmic compression means for logarith
mically compressing the output of said third ?lter
second channels;
?rst logarithmic compression means for logarithmi
cally compressing the output of said second ?lter
means;
?rst limiting means for limiting the level of the output
of said ?rst logarithmic compression means;
second limiting mans for limiting the level of the
means;
second logarithmic compression means for logarith
mically compressing the output of said fourth ?lter
output of said second logarithmic compression
means;
means; and
third logarithmic compression means for logarithmi
cally compressing the output of said ?fth ?lter
means for adding the outputs of said ?rst limiting
means, said second limiting means, and said ?rst
means;
?lter means
?rst limiting means for limiting the level of the output
6. A sound reproduction device including an auto
matic loudness compensator for compensating a sound
20
level of an audio signal, comprising;
means for increasing a ?rst level of sound pressure of
said audio signal in a ?rst range of sound frequency
of said third logarithmic compression means;
?rst adding means for adding the outputs of said ?rst
?lter means, said ?rst logarithmic compression
_ means and said ?rst limiting means to form an
relative to a second level of sound pressure in a
audio output signal in said ?rst channel; and
second adding means for adding the outputs of said
middle range of sound frequency when a sound
level of said audio signal is lower than a reference
vthird ?lter means, said second logarithmic com
pression means, and said ?rst limiting means to
form an audio output signal in said second channel.
7. An automatic loudness compensator as in claim 6,
sound level;
means for decreasing said ?rst level of sound pressure
relative to said second level of sound pressure in
said middle range of sound frequency when said
sound level of said audio signal is higher than said
reference sound level;
?rst ?lter means for extracting a middle-frequency
sound range component from said audio signal in a
?rst channel;
further comprising:
second limiting means for limiting the level of the
output of said ?rst logarithmic compression means,
the output of said second limiting means being
provided to said ?rst adding means in place of the
output of said ?rst logarithmic compression means;
35
second ?lter means for extracting a high-frequency
sound range component from said audio signal in
said ?rst channel;
third ?lter means for extracting a middle-frequency
sound range component from said audio signal in a
and
third limiting means for limiting the level of the out
put of said second logarithmic compression means,
the output of said third limiting means being pro
vided to said second adding means in place of the
output of said second logarithmic compression
means.
i
second channel;
45
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55
65
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t
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