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JPH05184000

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DESCRIPTION JPH05184000
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
automatic sound field correction apparatus for an audio system, and in particular, in a car audio
system and a home audio system, an audio source signal output from a CD player, radio, tape
deck or the like is reproduced. The present invention relates to an automatic sound field
correction device for an audio system that can automatically correct the sound field
characteristics for faithfully reproducing the source.
[0002]
2. Description of the Related Art In an audio system, it is ideal to reproduce sound faithful to the
source, but in general, the frequency characteristics of the speaker and the frequency
characteristics of the sound reproduction space are not flat, so they are output from audio source
equipment The audio source signal is simply amplified by an amplifier, and just by speaker input,
it is not possible to hear the sound faithful to the source, and some kind of sound field correction
must be made.
[0003]
Therefore, conventionally, a sound field correction circuit such as a graphic equalizer is
interposed between an audio source device and an amplifier, and speaker reproduction is
performed while reproducing a special test signal such as pink noise, impulse noise, or test tone.
Pick up the sound with a microphone, analyze the frequency characteristics of the microphone
output (In the case of impulse noise, include Fourier transform such as FFT), perform sound field
correction with a sound field correction circuit, and obtain a flat sound reproduction
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characteristic I was on my mind.
[0004]
At this time, the user often performs sound field correction manually, but using a microcomputer,
analysis of the frequency characteristic of the microphone output, calculation of the optimum
correction amount, and sound field for the sound field correction circuit based on the calculation
result There is also a system in which flat sound reproduction characteristics are automatically
obtained by performing correction control.
Once the sound field characteristics have been corrected so as to obtain a flat sound
reproduction characteristic, the sound field correction is performed again when the type of
speaker is changed or the speaker arrangement is changed.
[0005]
However, in the above-mentioned conventional correction method of sound field characteristics,
a test recording medium on which a special test signal such as pink noise, impulse noise, test
tone, etc. is recorded is prepared, and the test is carried out. Recording media must be set in an
audio system for reproduction, and there is also a problem that the user hears unpleasant sounds
due to reproduction of these test signals.
Moreover, when performing sound field correction by manual operation, the effort was
troublesome.
[0006]
From the above, it is an object of the present invention to provide an automatic sound field
correction device for an audio system capable of automatically correcting the sound field
characteristics by reproducing a normal music source without using a special test signal. It is.
[0007]
According to one aspect of the present invention, there is provided an audio system including an
audio source device, a sound field correction circuit, an amplifier, and a speaker, the microphone
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picking up the speaker reproduction sound, and the band of the microphone output. First bandspecific signal level detection means for detecting another signal level, second band-specific
signal level detection means for detecting a band-specific signal level of an audio source signal
output from an audio source device, and first band-specific signal level From the detection output
of the detection means and the detection output of the second band-by-band signal level
detection means, the average detection level for a predetermined fixed time in the same period
on the microphone side and the audio source side is determined for each band. From the average
detection level for each side of the audio source side and the audio source side, the microphone
side frequency characteristic curve and the audio source side frequency characteristic Means for
calculating the relative difference between the microphones and sound field correction control
means for performing sound field correction control on the sound field correction circuit so as to
cancel out the relative difference between the microphone side frequency characteristic curve
and the audio source side frequency characteristic curve Is achieved by
[0008]
Further, according to another aspect of the present invention, in an audio system including an
audio source device, a sound field correction circuit, an amplifier, and a speaker, a microphone
picking up a speaker reproduction sound and a band-by-band signal level detection detecting a
band-by-band signal level. Means, time-division input means for time-dividing an audio source
signal outputted from the microphone output and the audio source device and inputting it to the
band-specific signal level detection means, and detection output of the band-specific signal level
detection means In addition, the average detection level for a predetermined constant time in the
same period on the microphone side and the audio source side is determined, and the
microphone side frequency characteristic curve and the audio source side are determined from
the average detection levels for the band on the microphone side and the audio source side.
Means for calculating relative difference of frequency characteristic curve, microphone side
frequency characteristic curve and audio source Is achieved by providing a sound field correction
control means for sound field correction control for sound field correction circuit so as to cancel
the relative difference of the frequency characteristic curve, the.
[0009]
According to one aspect of the present invention, the band-by-band signal level of the speaker
reproduction sound picked up by the microphone and the band-by-band signal level of the audio
source signal output from the audio device are separately detected. The average detection level
for a predetermined constant time in the same period of the microphone side and the audio
source side is determined, and the microphone side frequency characteristic curve and the audio
source side frequency characteristic are calculated from the average detection levels of the
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microphone side and the audio source side by band. The relative difference between the curves is
calculated, and sound field correction control is performed on the sound field correction circuit
so as to cancel the relative difference between the microphone side frequency characteristic
curve and the audio source side frequency characteristic curve.
As a result, since the sound field characteristics can be corrected using a normal music source
signal without using a special test signal, a test recording medium can be prepared, or the test
recording medium can be set in the system. Also, during the field correction, there is no
discomfort because normal music is heard.
Furthermore, since the sound field correction is automatically performed, it is not necessary to
perform the sound field correction manually.
Also, there is a delay time of several ms between the audio source signal output from the audio
source device and the microphone output of the audio source signal via the sound field
correction circuit, amplifier, speaker, and microphone. When sound field correction is performed
by comparing detection levels at the same point of time of the microphone output and the audio
source signal, the microphone output must be corrected in advance (the correction amount
differs depending on the frequency). Since the average detection level for a predetermined fixed
time in the same period on the microphone side and the audio source side is determined so that
an error due to delay does not occur, the correction of the microphone output becomes
unnecessary, and the configuration can be simplified. .
[0010]
Further, according to another aspect of the present invention, the band-specific signal level of the
speaker reproduction sound picked up by the microphone and the band-specific signal level of
the audio source signal output from the audio device are detected by time division. The average
detection level for a predetermined constant time in the same period on the microphone side and
the audio source side is determined, and the microphone side frequency characteristic curve and
the audio source side frequency are calculated from the average detection levels for the band on
the microphone side and the audio source side The relative difference between the characteristic
curves is calculated, and sound field correction control is performed on the sound field correction
circuit so as to cancel the relative difference between the microphone side frequency
characteristic curve and the audio source side frequency characteristic curve. As a result, it is
possible to detect the band-by-band signal level for the microphone output and the audio source
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signal using one band-by-band signal level detection means, and the configuration can be
simplified.
[0011]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is an overall block diagram
of a car audio system according to an embodiment of the present invention. In the figure, 10 is a
head unit (audio source device) such as a CD player, a radio, or a tape deck, and 12 is a sound
field correction circuit (graphic equalizer) that performs sound field correction on the audio
source signal output from the head unit. In this embodiment, as an example, the audio band is
equally divided into nine bands on the frequency axis (logarithmic axis) to perform sound field
correction. The central frequency points of the nine bands are 64 Hz, 125 Hz, 250 Hz, 500 Hz, 1
kHz, 2 kHz, 4 kHz, 8 kHz, 16 kHz, respectively. The sound field correction circuit 12 performs
sound field correction under sound field correction control of a microcomputer described later.
An amplifier 14 amplifies an audio source signal that has passed through the sound field
correction circuit, and a speaker 16 is driven by the amplifier.
[0012]
A microphone 18 picks up the reproduced sound from the speaker, a first band-specific signal
level detection circuit 20 detects a band-specific signal level of the microphone output, and 22 to
38 BPF for dividing the microphone output into nine bands 42 to Reference numeral 58 denotes
a DC detection circuit that DC-detects the output of each BPF individually, and 62 to 78 denote
smoothing circuits that individually smooth the output of each DC detection circuit. The center
frequencies of the BPFs 22 to 38 are 64 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz,
16 kHz as in the center frequency point of the sound field correction circuit. The band-by-band
detection level signal of the microphone output is output from the conversion circuits 62-78.
[0013]
80 is a second band-specific signal level detection circuit for detecting the band-specific signal
level of the audio source signal output from the head unit, 82 to 98 are BPFs for dividing the
audio source signal into nine bands, and 102 to 118 are each A DC detection circuit individually
DC-detects the output of the BPF, and a smoothing circuit 120-138 individually smoothes the
output of each DC detection circuit. Each of the BPFs 82 to 98 has the same band pass
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characteristics as the BPFs 22 to 38 on the microphone side, and the center frequency of each
passband is 64 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 16 kHz, and the
bandwise detection level signals of the audio source signal are output from the smoothing
circuits 122 to 138.
[0014]
A first multiplexer 140 switches and outputs each detection output of the first band-specific
signal level detection circuit in time division, and a second multiplexer 142 switches and outputs
each output of the second band-specific signal level detection circuit in time division , 144 is a
first A / D unit for A / D converting the output of the first multiplexer, 146 is a second A / D unit
for A / D converting the output of the second multiplexer, 148 is an automatic correction for
instructing automatic sound field correction An instruction key 150 is a microcomputer that
performs a predetermined automatic sound field correction process when an automatic
correction instruction key is pressed and an automatic sound field correction is instructed. The
microcomputer 150 performs synchronous switching control of the first multiplexer and the
second multiplexer, and inputs band-specific detection level data on the microphone output and
the audio source signal from the first A / D converter and the second A / D converter. For each
band, the average detection level of a predetermined constant time in the same period of the
microphone side and the audio source side is determined, and further, the microphone side
frequency characteristic is calculated from the average detection level according to the
determined band of the microphone side and the audio source side The relative difference
between the curve and the audio source side frequency characteristic curve is calculated, and the
sound field correction control for the sound field correction circuit is performed so as to cancel
the relative difference between the microphone side frequency characteristic curve and the audio
source side frequency characteristic curve.
[0015]
FIG. 2 is a flowchart showing automatic sound field correction processing by the microcomputer
150, and FIGS. 3 and 4 are explanatory diagrams of the automatic sound field correction
operation, which will be described below with reference to these drawings. Here, the sound field
correction circuit 12 can perform sound field correction (gain adjustment) in 1 dB steps within a
range of ± 15 dB in each band here, and the RAM 152 of the microcomputer 150 (refer to FIG.
1) In, the band-by-band gain data G1 to G9 currently set in the sound field correction circuit 12
are registered (Gi indicates the gain of the divided band counted from the low band side on the
frequency axis). , G1 is a gain at a center frequency of 64 Hz, G2 is a gain at 125 Hz, G3 is a gain
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at 250 Hz,..., G9 is a gain at 16 kHz. See equalizer curve EQC in FIG. 4).
[0016]
Now, when the car audio system shown in FIG. 1 is in the normal playing state, the normal audio
source signal output from the head unit 10 is subjected to the sound field correction by the
sound field correction circuit 12 (however, the sound field correction circuit If the frequency
characteristic is set to be flat, no sound field correction is applied), the signal is amplified by the
amplifier 14 and then input to the speaker 16 to be reproduced as sound from the speaker 16.
[0017]
At this time, the reproduced sound from the speaker 16 is picked up by the microphone 18, and
the signal level is detected by the first band-specific signal level detection circuit 20 for every
nine bands equally divided on the frequency axis, and the band-specific detection A level signal is
output.
In addition, as for the audio source signal output from the head unit 10, the signal level is
detected by the second band-specific signal level detection circuit 80 for each of nine bands
equally divided on the frequency axis as in the microphone side. Another detection level signal is
output.
[0018]
In this state, when the user wants to cancel the influence of the frequency characteristic of the
speaker 16 and the frequency characteristic of the vehicle interior sound reproduction space and
wants to listen to music with a flat characteristic faithful to the source, he presses the automatic
correction instruction key 98, The microcomputer 150 is instructed to perform automatic sound
field correction. Receiving this instruction, the microcomputer 150 starts switching control of the
first multiplexer 140 and the second multiplexer 142, and switches them in synchronization at
high speed (steps 101 and 102 in FIG. 2). Then, first, the detection level data of each band on the
microphone side output from the first A / D converter 144 is monitored, and if data of a certain
band exceeds a predetermined reference level (steps 103 and 104), Stop the switching control of
the first Markplexer 140 and the second multiplexer 142 (Step 105), and detect the detection
level by band from the first A / D converter 144 and the second A / D converter 146 in the
corresponding band on the microphone side and audio source side The data is input for a
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predetermined number of samples (a predetermined fixed time of about several hundreds of ms)
over the same period, added separately for the microphone side and the audio source side, and
then divided by the predetermined number of samples to obtain an average detection level. (Step
106), and are registered in the RAM 152 in association with the corresponding band separately
for the microphone side and the audio source side (step 10 ).
[0019]
When the above processing is completed for one band, the switching control of the first
multiplexer 140 and the second multiplexer 142 is resumed (steps 108 and 102), and the first A
/ A is removed except for the previously processed band. The detection level data for each band
on the microphone side output from the D converter 144 is monitored, and if data in a certain
band exceeds a predetermined reference level (steps 103 and 104), the first multiplexer 140 and
the second Stop switching control of the multiplexer 142 (step 105), and detect the band-byband detection level data of the corresponding band from the first A / D converter 144 and the
second A / D converter 146 by a predetermined number of samples Input, and then separately
added to the microphone side and the audio source side, and then divided by the predetermined
number of samples to find the average detection level And association with separate band
microphone side and audio source is registered in the RAM 152 (step 106, 107).
[0020]
Thereafter, the same processing is executed until the unprocessed band disappears.
If processing of all bands is completed (at this time, the switching between the first multiplexer
140 and the second multiplexer 142 remains stopped), for example, the microphone side and the
audio source side registered in the RAM 152 When the average detection level by band is in dB
units as shown by the solid line in FIG. 3 (the average detection level by bands on the
microphone side is ML1 to ML9, and the average detection level by bands on the audio source
side is AL1 to AL9 A relative difference between the microphone-side frequency characteristic
curve MC and the audio source-side frequency characteristic curve AC obtained by connecting
the average detection level of each band separately for the microphone side and the audio source
side is obtained.
[0021]
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There are various methods for determining the relative difference, but here, the average
detection level (AL5) on the audio source side in the fifth band (center frequency 1 kHz) matches
the average detection level ML5 on the microphone side , AL1 to AL9 are all expressed by the
following equation α, α = ML5 to AL5 to obtain corrected average detection levels AL1 'to AL9',
and then, for each band, the gain adjustment amount gi, gi = as a relative difference ALi'-MLi (i =
1 to 9) is obtained (step 109, see FIG. 3). However, it is g5 = 0.
[0022]
Next, the microcomputer 150 uses the calculated gain adjustment amounts g1 to g9 to apply to
the sound field correction circuit so as to cancel the relative difference between the microphone
side frequency characteristic curve (AC) and the audio source side frequency characteristic curve
(MC). Perform sound field correction control. Specifically, calculation of Gi ′ = Gi + gi (i = 1 to 9)
is performed using the setting sound field correction data Gi for each band in the sound field
correction circuit 12 registered in advance in the RAM 152 of the microcomputer 150. And
rewrite and register the G1 'to G9' in the RAM as new setting sound field correction data, and
output new sound field correction data G1 'to G9' for each band to the sound field correction
circuit 12, The gain of each band of the sound field correction circuit 12 is changed to G1 'to G9',
and g1 to g9 are varied for each band (step 110). As a result, the equalizer curve in the sound
field correction circuit 12 is as shown by EQC 'in FIG. If the equalizer curve of the sound field
correction circuit 12 before correction is flat and matched (G1 to G9 are all 0), then the gain of
each band of the sound field correction circuit 12 is g1 to g9. Become.
[0023]
In this way, the sound field correction control is performed so as to cancel the relative difference
between the microphone side frequency characteristic curve (MC) and the audio source side
frequency characteristic curve (AC). As a result, the setting in the sound field correction circuit
12 so far Regardless of the sound field correction characteristics, the user will be able to listen to
music under a flat frequency characteristic that is faithful to the source. Once the automatic
sound field correction is performed, if the type of speaker is changed or the speaker arrangement
is changed, the automatic correction field key may be pressed again to indicate the automatic
sound field correction.
[0024]
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According to this embodiment, even without using special test signals such as pink noise, impulse
noise and test tone signals, sound is obtained using signals obtained from ordinary music sources
such as music CDs, music tapes and music broadcasts. Since it is possible to perform field
correction, it is not necessary to prepare a test recording medium or to set the test recording
medium in the system, and it is also uncomfortable because normal music can be heard
continuously during sound field correction. There is no need to interrupt the music you have
been listening to until then. Furthermore, when automatic sound field correction is indicated by
the automatic correction instruction key, sound field correction is automatically performed by
the microcomputer, so that it is not time and effort to manually perform the sound field
correction operation.
[0025]
In addition, there is a delay time of several ms between the audio source signal output from the
head unit and the microphone output through the sound source correction circuit, amplifier,
speaker, and microphone of the audio source signal. When sound field correction is performed
based on the detection level at the same point of time of output and audio source signal, it is
necessary to correct the microphone output in advance, but for each band, the same period of the
microphone side and the audio source side Since an average detection level for a predetermined
constant time in the above is determined so that an error due to delay does not occur, correction
of the microphone output becomes unnecessary, and the configuration can be simplified.
Furthermore, when the average detection level of a certain band is determined, the calculation
error can be reduced since the calculation is started at a point beyond a certain reference level.
[0026]
In the above-described embodiment, the microcomputer performs only the automatic sound field
correction processing, but the sound field characteristic adjustment operation unit is connected
so that any sound field characteristic instructed manually can be set. It is also good. Further, as
shown in FIG. 5, while connecting the spare display 154 to the microcomputer 150A, the output
of the head unit 10 and the output of the sound field correction circuit 12 are switched to the
input side of the second band-specific signal level detection circuit 80. A changeover switch 156
for inputting is added, and when performing automatic sound field correction processing, the
change switch 156 is switched to the output side of the head unit 10, and automatic sound field
correction processing is performed in exactly the same manner as described above. When the
sound field correction processing is not performed, the changeover switch 156 is switched to the
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output side of the sound field correction circuit 12 and the switching control of the second
multiplexer 142 is performed to detect each band from the second A / D converter 146 Level
data is input, and based on the detection level data, a spanner display control for the spanner
display 154 is performed. It may be carried out.
[0027]
Further, although in the embodiment of FIG. 1, the band-specific signal level detection circuit, the
multiplexer and the A / D converter are separately provided on the microphone side and the
audio source side, as shown in FIG. , The multiplexer 160 and the A / D converter 162 are
provided only, and the multiplexer 164 for inputting the microphone output and the audio
source signal on a time-division basis is provided on the input side of the band-specific signal
level detection circuit 158. At this time, the microcomputer 150B starts high-speed switching
control of the multiplexer 164 and controls the multiplexer 160 to switch to the next position
every time the switching of the multiplexer 164 makes one cycle, and the multiplexer 164 is on
the microphone side. Sometimes, it is outputted from A / D converter 162 per certain band When
the output level data exceeds the predetermined reference level, the switching of multiplexer 160
is stopped while switching of multiplexer 164 is continued, and the average detection level of the
microphone side and the audio source side in the same band and the same period is stopped.
After calculating and processing for one band, the switching of multiplexer 160 is restarted, and
the same processing is performed for the other unprocessed bands, and the average detection
level by band on the microphone side and the audio source side You may ask for In this way, the
configuration can be simplified because the band-specific signal level detection circuit and the A
/ D converter can be one set.
[0028]
Further, in the embodiment of FIG. 1, calculation of the average detection level for each band is
performed by the microcomputer, but as shown in FIG. 7, the outputs of the first A / D converter
144 and the second A / D converter 146 Is input to a DSP (digital signal processor) 166, and the
DSP 166 calculates an average detection level by band on the microphone side and the audio
source side, outputs the result to the microcomputer 150C, and the microphone 150C By
performing sound field correction control based on the relative difference between the side
frequency characteristic curve and the audio source side frequency characteristic curve, the load
on the microcomputer 150C can be greatly reduced, and even during the automatic sound field
correction processing. And other processing such as display of subcode information of a CD can
be performed without difficulty. When a DSP is used to calculate the average detection level by
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band as shown in FIG. 7, the sound field correction circuit itself can also be shared by one DSP
when it is realized using the DSP.
[0029]
Further, as shown in FIG. 8, the output of the microphone 18 is digitized by the first A / D
converter 144 and input to the DSP 166A, and the output of the head unit 10 is also digitized by
the second A / D converter 146 to the DSP 166A. The signal is input and the filtering process is
performed by the DSP 166A to calculate the band-by-band signal level and the band-by-band
average signal level separately for each of the microphone side and the audio source side, and
calculate the result as a microcomputer By outputting sound to 150 C and performing sound
field correction control based on the relative difference between the microphone side frequency
characteristic curve and the audio source side frequency characteristic curve in the
microcomputer 150 C, the load on the microcomputer 150 C is greatly reduced. At the same
time, it also eliminates the need for hard-wired signal level detection circuits by hardware. That.
[0030]
Further, although the car audio system has been described as an example in the above-described
embodiment and each modification, the present invention is not limited to this, and can be
similarly applied to home audio systems and the like.
[0031]
According to one aspect of the present invention, the band-specific signal level of the speaker
reproduction sound picked up by the microphone and the band-specific signal level of the audio
source signal output from the audio device are separately detected, and each band is detected.
Every time, the average detection level of a predetermined constant time in the same period of
the microphone side and the audio source side is determined, and the microphone side frequency
characteristic curve and the audio source are calculated from the average detection levels of the
microphone side and the audio source side by band. Since the relative difference between the
side frequency characteristic curve is calculated and the sound field correction control for the
sound field correction circuit is performed so as to cancel the relative difference between the
microphone side frequency characteristic curve and the audio source side frequency
characteristic curve, a special test Since the sound field characteristics can be corrected using a
normal music source signal without using a signal, a test recording medium is prepared. Ri, it is
not necessary or to set the test for the recording medium to the system, also, in the sound field
correction, discomfort does not occur because the normal music is heard.
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Furthermore, since the sound field correction is automatically performed, it is not necessary to
perform the sound field correction operation manually.
Also, there is a delay time of several ms between the audio source signal output from the audio
source device and the microphone output of the audio source signal via the sound field
correction circuit, amplifier, speaker, and microphone. When sound field correction is performed
based on the detection level at the same time of the microphone output and the audio source
signal, the microphone output must be corrected in advance. However, for each band, the
microphone side and the audio source side are the same. Since an average detection level for a
predetermined constant time in a period is determined so as not to cause an error due to delay,
correction of the microphone output is unnecessary, and the configuration can be simplified.
[0032]
Further, according to another aspect of the present invention, the band-by-band signal level of
the speaker reproduction sound picked up by the microphone and the band-by-band signal level
of the audio source signal output from the audio device are detected by time division. In addition,
the average detection level for a predetermined constant time in the same period on the
microphone side and the audio source side is determined, and the microphone side frequency
characteristic curve and the audio source side are determined from the average detection levels
for the band on the microphone side and the audio source side. Since the relative difference
between the frequency characteristic curves is calculated and the sound field correction control
for the sound field correction circuit is performed so as to cancel the relative difference between
the microphone side frequency characteristic curve and the audio source side frequency
characteristic curve, The signal level detection means can be used to detect the band-by-band
signal level for the microphone output and the audio source signal. It is possible to make the
configuration easier.
[0033]
Brief description of the drawings
[0034]
1 is an overall configuration diagram of a car audio system according to an embodiment of the
present invention.
[0035]
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2 is a flowchart showing automatic sound field correction processing.
[0036]
3 is an explanatory view of the automatic sound field correction operation.
[0037]
4 is an explanatory view of the automatic sound field correction operation.
[0038]
5 is an overall configuration diagram showing a modification of the present invention.
[0039]
6 is an overall configuration diagram showing another modified example of the present
invention.
[0040]
7 is an overall configuration diagram showing another modified example of the present
invention.
[0041]
8 is an overall configuration diagram showing another modification according to the present
invention.
[0042]
Explanation of sign
[0043]
DESCRIPTION OF SYMBOLS 10 Head unit 12 Sound field correction circuit 14 Amplifier 16
Speaker 18 Microphone 20 1st band classified signal level detection circuit 80 2nd band
classified signal level detection circuit 140 1st multiplexer 142 2nd multiplexer 148 Automatic
correction instruction key 150, 150A, 150B , 150C microcomputer 158 band-specific signal level
detection circuit 164 multiplexer 166, 166A DSP
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