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JPH04123692

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Notice
This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH04123692
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
device for correcting the frequency characteristics of reproduction sounds for vehicles, etc., and
in particular, the frequency characteristics that the sound output from the speaker changes
before reaching the listener Device for correcting
[0002]
2. Description of the Related Art In an on-vehicle music signal reproduction apparatus, even if the
frequency characteristic of the speaker itself is flat, generally the sound emitted from the speaker
is reflected to a wall or the like before reaching the listener's ear As a result, the frequency
characteristic changes. As a frequency characteristic correction device for reproduction sound
for correcting it, the one having the configuration shown in FIG. 2 is conventionally known.
[0003]
In FIG. 2, 1 is a signal generation circuit, 2 is a microphone, 3 is a signal processing unit, 4 is an
FIR filter, 5 is a multiplexer, 6 is a control unit such as a microcomputer, 7 is an amplifier, and 8
is a speaker.
[0004]
10-05-2019
1
First, in order to measure the transmission frequency characteristic, the multiplexer 5 is on the
signal generating circuit 1 side, and the impulse (FIG. 3A) generated by the signal generating
circuit 1 is transmitted from the speaker 8 through the amplifier 7. generate.
The sound is picked up by the microphone 2 (FIG. 3 (b)), and the signal processing unit 3
performs FFT processing to obtain the transmission frequency characteristic (solid line in FIG. 3
(c)) and its neighboring characteristic (FIG. 3) The dotted line (c) is obtained, and an IFFT (inverse
FFT) process is performed to obtain an impulse response (FIG. 3 (d)) of the inverse characteristic.
[0005]
The sample values of the impulse response are set, for example, as filter coefficients a0, a1,..., An
of the FIR (finite impulse response) filter 4 having the configuration shown in FIG. In FIG. 8, T1 to
Tn are delay circuits, a0 to an are coefficients (multipliers), and ADD is an adder. Control of the
setting of the filter coefficient, switching of the multiplexer 5 and the like is all performed by the
control unit 6. Note that, during normal music reproduction, the multiplexer 5 is switched to the
FIR filter 4 side.
[0006]
[0006] In such a conventional device, when used in an environment where background noise
changes, such as in a car interior, the drawback is that the sound quality changes depending on
the background noise state. there were. In addition, it takes a considerable amount of time to
obtain transmission frequency characteristics, and the use of an FIR filter causes a problem that
the circuit scale becomes large.
[0007]
The object of the present invention is to correct the transmission frequency characteristic
according to the state of background noise, to reduce the change in sound quality, and to
perform the measurement and correction of the transmission frequency characteristic in a short
time. It is an object of the present invention to provide a frequency characteristic correction
device of
10-05-2019
2
[0008]
SUMMARY OF THE INVENTION In order to achieve the above object, according to the present
invention, there is provided a noise generating unit for generating a predetermined noise sound,
and a listening apparatus provided in the vicinity of a listener and including the noise sound. A
microphone for taking in sound and background noise, a filter unit for dividing and outputting
the noise sound and background noise taken in by the microphone for each of different
predetermined frequency bands, and for each frequency band output from the filter unit A
transmission frequency characteristic calculation unit that obtains the power of sound and
calculates transmission frequency characteristics of noise sound and background noise, a
reproduction sound detection unit that detects an input signal level of reproduction sound that a
listener listens to, and the reproduction sound detection unit When there is no reproduced sound
detected in step 2, change the parameters of the filter unit to correspond to the change in
background noise, and then calculate the transmission frequency characteristics of the
background noise and the transmission frequency calculated by the operation unit. Seeking
synthesized synthesized frequency characteristic of the inverse characteristic of the frequency
characteristic, characterized in that comprising a correction control unit that performs control for
correcting the frequency characteristic of the filter unit.
[0009]
In the present invention, the noise noise and the background noise taken in by the microphone
are divided into frequency bands by the filter unit, and the transmission frequency characteristic
calculated by finding the power of the sound and the reproduced sound are absent. A composite
frequency characteristic is obtained by combining the inverse characteristic of the transmission
frequency characteristic corresponding to the background noise at the time, and control is
performed to correct the frequency characteristic of the filter unit.
Therefore, the measurement and correction of the transmission frequency characteristic can be
performed in a short time, and furthermore, the transmission frequency characteristic can be
corrected according to the state of the background noise, and the change of the sound quality
can be reduced.
[0010]
Embodiments of the present invention will now be described in detail with reference to the
drawings.
10-05-2019
3
FIG. 1 shows the configuration of one embodiment of a transmission frequency characteristic
correction device according to the present invention, 11 is a random noise generating circuit, 12
and 13 are multiplexers, 14 is a signal processing unit, 15 is a signal level monitoring circuit, 16
is 2 shows a control unit.
[0011]
In the present invention, an IIR (Infinite Impulse Response) filter is used as a filter for
transmission characteristic and background noise spectrum measurement and transmission
characteristic correction (switching of both filters is carried out only by changing the filter
coefficient. End). The operation of the present apparatus is divided into measurement of
transmission frequency characteristics and correction of transmission frequency characteristics
as shown in the flowchart of FIG.
[0012]
The operation of FIG. 1 will be described in detail with reference to FIG. First, an operation at the
time of measurement of transmission frequency characteristics will be described. First, in order
to measure the transmission frequency characteristics, the multiplexer 13 is set to the random
noise generating circuit 11 side, and the random noise generated by the signal generating circuit
11 is generated from the speaker 8 via the amplifier 7 (step 21 in FIG. 4).
[0013]
As shown in FIG. 5, the microphone 2 is installed at the position of the listener's ear in the vehicle
interior 17, and random noise from the speaker 8 is picked up by the microphone 2. The power
of each frequency band is calculated using an IIR filter configured in the signal processing unit
14 to obtain a transmission frequency characteristic. A band pass filter of several bands is
configured by the IIR filter, and the transmission characteristic is determined based on the output
level of each filter.
[0014]
10-05-2019
4
Further, the inverse characteristic of the obtained transmission characteristic is obtained. For
example, if 300 to 400 Hz is 6 dB lower than the other frequency bands, a filter coefficient (IIR
filter) can be calculated or held in advance in a memory or the like so that the characteristic is
such that 6 dB is raised. From among them, bring it and set it (step 4 in FIG. 4). The control unit
16 performs these processes.
[0015]
Next, the operation at the time of correction of the transmission frequency characteristic will be
described. The generation of random noise is stopped (step 24 in FIG. 4), the multiplexer 13 is
switched to the signal processing unit 14 side, and correction is performed by the filter
(correction IIR filter) obtained by the above processing (step 25 in FIG. 4).
[0016]
At this point, the frequency characteristic (spectrum) of the background noise is flat. Also,
separately from the above processing, the level of the input signal is monitored by the signal
level monitoring circuit 15 (step 26 in FIG. 4), and it is detected again that the input signal has
been interrupted due to tape rewinding or stopping. The coefficients of the IIR filter are changed
to be the same band pass filter as in the first measurement, and the frequency characteristic
(spectrum) of the background noise is measured (step 27 in FIG. 4). At this time, for example, if
the vehicle is running, it exhibits a characteristic in which the low band is raised by 10 dB or
more due to road noise or the like, and generally the bass is masked by this noise and the bass
feeling is reduced.
[0017]
Therefore, in order to compensate for this, as shown in FIG. 6, the inverse characteristic of the
transmission frequency characteristic shown by a solid line is shown by a dotted line. The
frequency characteristic of the background noise thus measured is corrected (step 28 in FIG. 4)
to obtain the frequency characteristic indicated by the one-dot chain line. In practice, this
correction is performed by changing the coefficients of the IIR filter (during correction).
10-05-2019
5
[0018]
That is, assuming that the characteristic has been raised by 2 dB in the 100 to 200 Hz band, if
the characteristic of the background noise is raised above 11 dB and so on, it becomes an IIR
filter that raises the characteristic by 11 + 2 = 13 dB, Change the coefficients of the IIR filter.
Repeat the above operation.
[0019]
FIG. 7 shows an example of the construction of an IIR filter which can be used in the present
invention, which comprises delay circuits 31 to 34, coefficient (multiplier) units 41 to 45 and an
adder 51. Comparing the conventional FIR filter with the IIR filter shown in FIG. 7, when creating
a filter with the same amplitude characteristic (VS frequency characteristic), the IIR filter is FIR in
the hardware scale (scale of delay circuit and multiplier). It is 5 to 10 times smaller than the
filter. In addition, although the FIR filter takes convergence time and takes a considerable amount
of time to obtain the transmission frequency characteristic, the IIR filter does not have such a
problem.
[0020]
FIG. 8 shows the construction of another embodiment of the transmission frequency
characteristic correction apparatus according to the present invention, in which 18 indicates a
digital signal processor DSP and 19 indicates a microcomputer. In this embodiment, the control
unit 16 is realized by the microcomputer 19 and the other processing units are realized by the
DSP 18. Further, as another embodiment, all processing may be performed by the DSP.
[0021]
As described above, according to the frequency characteristic correction device of the present
invention, since the transmission frequency characteristic is corrected according to the state of
the background noise, the sound quality changes due to the background noise. Can be reduced.
[0022]
Brief description of the drawings
10-05-2019
6
[0023]
1 is a block diagram showing the configuration of an embodiment of the transmission frequency
characteristic correction device according to the present invention.
[0024]
2 is a block diagram showing a configuration of a conventional transmission frequency
characteristic correction device.
[0025]
3 is a characteristic diagram for explaining the processing of the correction device of FIG.
[0026]
4 is a flowchart showing the processing of the correction device of FIG.
[0027]
5 is a diagram showing an example of the arrangement of the microphone according to the
present invention.
[0028]
6 is a characteristic diagram illustrating an embodiment of the present invention.
[0029]
7 is a block diagram showing a configuration example of the IIR filter of FIG.
[0030]
FIG. 8 is a block diagram of another embodiment of the transmission frequency characteristic
correction device according to the present invention.
[0031]
9 is a block diagram showing the configuration of the FIR filter of FIG.
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7
[0032]
Explanation of sign
[0033]
Reference Signs List 2 microphone 8 speaker 11 random noise generation circuit 12, 13
multiplexer 14 signal processing unit 15 signal level monitoring circuit 16 control unit
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