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DESCRIPTION JP2007129375

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DESCRIPTION JP2007129375
An object of the present invention is to suppress a level change of background noise in voiced
and unvoiced states, thereby preventing a sense of incongruity and increasing speech
intelligibility. A band divider divides an input signal into a plurality of frequency bands and cuts
out the band output signal for each frequency band. The level calculator 31 integrates the values
of the band output signals with respect to the frequency division bandwidth to calculate the level
value for each frequency band. The level controller 33 corrects the level value of each band so as
to have a correlation with the adjacent band with respect to the calculated level value of each
band, and outputs the corrected level value of each band. The amplifier 32 determines the
amplification factor based on the level value of each band output from the level controller,
amplifies and attenuates the band output signal with the determined amplification factor, and
outputs it as a compander output signal of each divided band Do. [Selected figure] Figure 1
Audio signal processing device
[0001]
The present invention relates to an audio signal processing apparatus, and more particularly to
audio signal processing using a level companding circuit (referred to as a compander).
[0002]
FIG. 6 is a block diagram showing a conventional basic configuration of audio signal processing
using a compander (see, for example, Patent Document 1).
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As shown in FIG. 6, the conventional compander 3-1 comprises a level calculator 31-1 and an
amplifier 32-1. S1 represents an input signal, and S2 represents an output signal.
[0003]
The level calculator 31-1 calculates the signal power of the input signal S1 including voice and
background noise, and the amplifier 32 based on the input / output characteristics of the
compander 3-1 shown in FIG. 3 according to the level value of the input signal S1. Change the
amplification factor of -1. That is, since a voice whose level is relatively high compared to
background noise is present in the area shown in area 2 of FIG. 3, it is amplified by the amplifier
32-1. On the other hand, background noise having a relatively low level compared to speech is
present in the area shown in area 1 of FIG. 3 and therefore is attenuated by amplifier 32-1 and
output as output signal S2. In this way, high level speech is amplified and low level background
noise is attenuated thereby increasing the speech intelligibility of the output signal S2.
[0004]
When the amplified acoustic signal is divided into a frequency band mainly containing wind
noise and a frequency band mainly containing human voice, and the output signal of the
amplifier in a frequency band mainly containing wind noise is wind noise There is known a
microphone amplification device in which a constant amount of attenuation is electronically
attenuated (see, for example, Patent Document 2).
[0005]
JP-A-58-148532 (page 2, FIG. 1, FIG. 2) JP-A-6-29764 (page 2, FIG. 1)
[0006]
In the technique described in Patent Document 1 described above, even if background noise is
attenuated when voiceless and amplified with voice when voiced, when the level of background
noise is small, the output level difference between background noise when voiced and voiceless is
It is slight.
However, when the background noise level is large, there is a problem that the output level
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difference of the background noise becomes remarkable between voiced and unvoiced and the
receiver feels uncomfortable.
[0007]
Further, in the technology described in Patent Document 2 described above, the frequency band
of the wind noise component is set to 20 Hz to about 150 Hz, and the output signal of the
amplifier is attenuated in this range. There is a problem that is not effective.
[0008]
Therefore, the first object of the present invention is to reduce the background noise from being
superimposed on the voice even when the background noise level is large, and to reduce the
difference in the background noise level between voiced and unvoiced. An object of the present
invention is to provide an audio signal processing apparatus in which a receiver's sense of
discomfort is suppressed.
[0009]
A second object of the present invention is to provide an audio signal processing apparatus
capable of achieving the above object even against background noise present in discrete
frequency bands.
[0010]
A speech signal processing apparatus according to the present invention is a speech signal
processing apparatus using a compander, which divides an input signal (S1 in FIG. 1) into a
plurality of frequency bands and cuts out the band output signal for each frequency band (FIG.
1). 1) and the level calculator (31 in FIG. 1) which calculates the level value for each frequency
band by integrating the values of the band output signals with respect to the frequency division
bandwidth, and the calculated level values of each band A level controller (33 in FIG. 1) that
corrects the level value of each band so as to have correlation with the adjacent bands and
outputs the corrected level value of each band, and for each band output from the level controller
The amplification factor is determined based on the level value, and the band output signal is
amplified and attenuated at the determined amplification factor, and an amplifier (32 in FIG. 1)
that outputs it as a compander output signal of each divided band and the compander output
signal Synthesized output signal And having a band synthesis portion for outputting S2) of FIG. 1
(2 in Figure 1).
[0011]
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Specifically, the level controller increases the weight for the band adjacent to the level control
target band, decreases the weight for the band farther away, and corresponds to the distance on
the frequency axis from the level control band. It is characterized in that correction is performed
by multiplying the level value by the weighting factor whose value has been attenuated.
[0012]
Also, the amplifier is characterized in that it amplifies a signal having a large level value of each
band output from the level controller and attenuates a signal having a small level value.
[0013]
In the present invention, an input signal is divided for each frequency band, the signal level for
each divided band is calculated, and based on the signal level for each band, a signal having a
large signal level is amplified by the compander with respect to the signal for each band.
Attenuates signals with small signal levels.
This makes it possible to prevent errors such as background noise amplification at the same time
as speech by amplifying and attenuating based on the signal level of the entire frequency band as
in the conventional system, and exists outside the speech band Even discrete background noises
can be attenuated to effectively amplify only the voice band.
[0014]
The signal level value of each divided band may be controlled, and the signal level value of
adjacent bands may be multiplied by a weighting factor to have a correlation with the signal level
value.
Thereby, it is possible to suppress a significant change in the frequency characteristics of the
input signal and the output signal accompanying amplification and attenuation of the signal by
the compander based on the signal level of each divided band.
[0015]
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The first effect of the present invention is that it reduces the background noise from being
superimposed on the voice, can suppress the change in the level of the background noise in
voiced and unvoiced, and can not make the receiver feel uncomfortable. is there.
The reason is that the input signal is divided by the frequency band, and the signal is amplified
and attenuated by the compander for each band, thereby attenuating background noise existing
on bands other than voice even when voiced, and when voiced and unvoiced This is because the
level of background noise can be made close to constant.
[0016]
The second effect of the present invention is to weight the level value of each band to be
correlated, correct the level value of each band, and control the amplification factor of the
amplifier for each band in the frequency band. A significant change in the frequency
characteristics of the input signal and the output signal due to the division can be suppressed,
which also prevents the receiver from feeling uncomfortable.
[0017]
Next, embodiments of the present invention will be described in detail with reference to the
drawings.
FIG. 1 is a block diagram showing the configuration of the audio signal processing apparatus
according to the present invention. This audio signal processing apparatus performs audio signal
processing on an input signal S1 including audio and background noise to enable voiced voice
and unvoiced voice. An output signal S2 is output which reduces the sense of incongruity of the
receiver by reducing the level difference of the background noise at the time.
As means for this purpose, this audio signal processing apparatus comprises a band dividing unit
1, a band combining unit 2 and a compander 3, and the compander 3 further comprises a level
calculator 31, a level controller 32 and an amplifier 33.
[0018]
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The band division unit 1 divides the input signal S1 into 16 frequency bands, and cuts out the
input signal S1 into band output signals A0 to A15 for each frequency band.
Specifically, the band division unit 1 includes band pass filters corresponding to the band output
signals A0 to A15 in one-to-one correspondence, and divides 0 Hz to 8000 Hz into bands 0 to 15
at 500 Hz intervals.
FIG. 2 shows the frequency characteristics of the gain for bands 0-15.
[0019]
The level calculator 31 of the compander 3 integrates the values of the band output signals A0 to
A15 with respect to the frequency division bandwidth 500 Hz to calculate level values (signal
powers) B0 to B15 for each frequency band.
[0020]
The level controller 33 corrects the level value of each of the bands after correction so that the
level value B0 to B15 of each of the bands calculated by the level calculator 31 has a correlation
with the adjacent band. The level values C0 to C15 are output.
The corrected level value of the band i (i = 0 to 15) is obtained as the corrected level value L (i)
by Equation (1).
<img class = "EMIRef" id = "201337301-00003" />
[0021]
In equation (1), c is a weighting ratio, and the value is between 0 and 1. The larger the value of c,
the stronger the correlation, and the smaller the value of c, the weaker the correlation. b is a
band number, and L (b) is a level value of each band b (= 0 to 15). A power value (shown in
(Expression 2)) in which the absolute value of (i−b) with respect to c is the power of
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multiplication is a weighting factor by which the level value L (i) is multiplied. This coefficient is
1 for any i at i = b. <img class = "EMIRef" id = "201337301-00004" />
[0022]
FIG. 3 is a graph showing values of weighting coefficients to be multiplied with respect to bands
b = 0 to 15 when c = 0.1 with respect to each case of i = 6 and i = 7. It can be seen from equation
(2) that this graph is symmetrical. Regardless of the value of i, the coefficient is 1 for i = b and
0.1 for i = b ± 1.
[0023]
The amplifier 32 determines the amplification factor based on the input / output characteristics
shown in FIG. 4 based on the level values C0 to C15 of each band output from the level controller
33. Then, the band output signals A0 to A15 from the band dividing unit 1 are amplified and
attenuated at the determined amplification factor, and output as the compander output signals
D0 to D15 of the divided bands.
[0024]
In FIG. 4, the solid line indicates the characteristic of the compander and the dotted line indicates
the amplification factor of 1. The amplification factor is 1 or more in area 2 where the input
signal level is 0 to −46 dB, and the amplification factor is 1 or less in areas 1 and 3 on both
sides of area 2. The horizontal axis of the solid line in FIG. 4 indicates the band output signals A0
to A15, and the vertical axis indicates the compander output signals D0 to D15.
[0025]
The band combining unit 2 combines the divided compander output signals D0 to D15 of each
band, and outputs an output signal S2.
[0026]
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Next, the operation of the embodiment of the present invention will be described.
The input signal S1 is divided by the band dividing unit 1 into bands 0 to 15 of 500 Hz intervals
from 0 Hz to 8000 Hz according to the frequency characteristics shown in FIG. 2, and the band
output signals A0 to A15 are level calculator 31 and amplifier It is output to 33. The band output
signals A0 to A15 input to the level calculator 31 are integrated with respect to the frequency
division bandwidth 500 Hz, and level values B0 to B15 for each frequency band are calculated.
That is, assuming that the band output signal A0 and the level value B0 correspond to a band of
0 Hz to 500 Hz, the level value B0 is obtained by integrating the level value of the band output
signal A0 over 0 Hz to 500 Hz.
[0027]
The amplifier 32 amplifies the band output signals A0 to A15 from the band division unit 1 and
outputs compander output signals D0 to D15 in accordance with the characteristics of the
compander shown in FIG. The amplification factor at this time is obtained by dividing the
difference between the solid line and the dotted line in FIG. 4 by the level value C0 to C15 from
the level controller 33 by the input signal level. In FIG. 4, there is a peak of amplification factor
near -20 Db.
[0028]
The above calculated level values B0 to B15 are independent for each band, and correlation of
signal levels between adjacent bands is ignored. Therefore, the level controller 33 outputs level
values C0 to C15 in which the level values B0 to B15 are weighted according to the weighting
factors shown in equation (2) and FIG. 3 in consideration of the level values of the adjacent
bands. The weighting factor changes the weighting according to the absolute value of (i−b)
which is the distance on the frequency axis from the band i to be controlled of the level values B0
to B15. In the case of c = 1, correction is made by adding the adjacent band at less than 10% of
the level value and the separated band at about 1% of the level value to the level value of the
band to be controlled. Become.
[0029]
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With such corrected level values C0 to C15, the amplifier 32 determines the amplification factor
for each band according to the input / output characteristics of FIG. 4, and amplifies each of the
band output signals A0 to A15 with the corresponding amplification factor. The speech is
amplified by the amplifier 32 since it is in the area shown in area 2 of FIG. 4 and, in general, the
background noise is attenuated by the amplifier 32 since it is in the area shown in area 1 of FIG.
The compander output signals D0 to D15 of each band are input to the band combining unit 2
and an output signal Ss2 is obtained after band combining.
[0030]
The frequency characteristics of the input signal and the output signal in this embodiment are
shown in FIG. It can be seen that the level difference between the output signal and the input
signal is significant and amplified in the audio part, that is, the part where the level difference
between the input signal and the noise is significant, as at point B in FIG. On the other hand, it
can be seen that the background noise portion, that is, the input signal at a level close to that of
the input signal, such as points A, C, and D, is not amplified. Also, no significant change in
frequency characteristics is observed due to frequency band division.
[0031]
The block diagram showing one embodiment of the audio signal processing apparatus of the
present invention The figure showing the gain of the divided frequency band The figure showing
the band characteristic of the weighting factor used for level control The figure showing the
input / output characteristic of the compander Showing the frequency characteristics of the
output signal and the block diagram showing the configuration of the prior art
Explanation of sign
[0032]
1 band division unit 2 band synthesis unit 3 compander 31 level calculator 32 amplifier 33 level
controller S1 input signal S2 output signal
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