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DESCRIPTION JP2012216924

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DESCRIPTION JP2012216924
The present invention provides a signal processing apparatus and a signal processing method
capable of efficiently specifying an upper limit value of a volume level without distortion.
SOLUTION: An acoustic signal output means 11 for outputting an acoustic signal, a control
means 12 for gradually increasing a volume level of the acoustic signal, and an output for
outputting an acoustic signal after the adjustment of the volume level as a sound Means 14, a
sound pickup means 15 for picking up the sound output by the output means, a suppression
means 17 for suppressing an echo component of the acoustic signal from the sound pickup
signal picked up by the sound pickup means, the suppression Detecting means for measuring the
level of the residual echo component remaining in the collected sound signal and detecting the
discontinuous change of the level of the echo component based on the amount of change of the
level of the residual echo component between successive volume levels 18 and the control means
12 is configured such that, when a discontinuous change is detected by the detection means, the
volume level immediately before the discontinuous change is detected is not distorted. It is
obtained as the limit value. [Selected figure] Figure 1
Signal processing apparatus and signal processing method
[0001]
Embodiments of the present invention relate to a signal processing apparatus and a signal
processing method.
[0002]
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1
There is provided a technology for providing a desired listening environment by changing the
characteristics of an audio signal using a DSP (Digital Signal Processor) or the like.
For example, a technology has been proposed in which reproduced sound output from a speaker
or an earphone is picked up by a microphone, and the reproduced sound is corrected based on
frequency characteristics of the collected sound.
[0003]
JP 2007-235809 A
[0004]
However, in the prior art, although it is possible to acquire frequency characteristics from the
collected sound, since distortion generated as the volume increases is not taken into
consideration, acquisition of frequency characteristics with distortion occurring May be done.
In this case, since the acquired frequency characteristic does not become an accurate value, if the
acoustic signal is corrected based on the frequency characteristic, the sound quality may be
degraded.
[0005]
The present invention has been made in view of the above, and an object of the present invention
is to provide a signal processing apparatus and a signal processing method capable of efficiently
specifying the upper limit value of the volume level in which no distortion occurs.
[0006]
The signal processing apparatus according to the embodiment includes an acoustic signal output
unit, a volume adjustment unit, a control unit, an output unit, a sound collection unit, a
suppression unit, and a detection unit.
The acoustic signal output means outputs an acoustic signal. The volume adjusting means adjusts
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the volume level of the sound signal. The control means controls the volume adjustment means
to gradually increase the volume level. The output means outputs, as a sound, an audio signal
after the volume level has been adjusted. The sound collecting means picks up the sound output
by the output means. The suppression means performs suppression processing for suppressing
an echo component of the sound signal on the sound collection signal collected by the sound
collection means. The detection means measures the residual echo component level remaining in
the sound pickup signal after the suppression processing, and, based on the amount of change of
the residual echo component level between successive sound volume levels, discontinuing the
level of the echo component. Detect changes. Furthermore, the control means stops the increase
of the volume level when the detection means detects a discontinuous change, and the volume
level immediately before the discontinuous change is detected is an upper limit value of the
volume level at which no distortion occurs. Get as.
[0007]
FIG. 1 is a view schematically showing a configuration of a test signal reproduction system
provided in the signal processing device of the present embodiment. FIG. 2 is a diagram showing
an example of a filtered signal. FIG. 3 is a diagram showing an example of residual echo
component levels. FIG. 4 is a view schematically showing a configuration of a frequency
characteristic measurement system provided in the signal processing device of the present
embodiment. FIG. 5 is a view schematically showing a configuration of a content reproduction
system provided in the signal processing device of the present embodiment. FIG. 6 is a flowchart
showing a procedure of reverse characteristic setting processing performed by the signal
processing device of the present embodiment. FIG. 7 is a view schematically showing a
configuration of a test signal reproduction system according to a modification 1 of the
embodiment. FIG. 8 is a view showing an example of the residual echo component level in the
first modification. FIG. 9 is a view schematically showing a configuration of a test signal
reproduction system according to Modification 2 of the present embodiment.
[0008]
Hereinafter, the signal processing apparatus according to the present embodiment will be
described with reference to the drawings. The signal processing apparatus of this embodiment is
roughly classified into the following three systems according to functions. First, as a first system,
a test signal reproduction system 100 (see FIG. 1) is provided which specifies an upper limit
value of a volume level at which non-linear distortion (hereinafter referred to as non-linear
distortion) does not occur. In addition, as a second system, a frequency characteristic
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measurement system 200 (see FIG. 4) for measuring the frequency characteristic of the signal
processing apparatus (speaker 14) in the range of the volume level specified by the test signal
reproduction system 100 is provided. Also, as a third system, a content reproduction system 300
that corrects and reproduces the frequency characteristics of contents such as audio signals and
audio signals using the inverse characteristic of the frequency characteristic measured by the
frequency characteristic measurement system 200 (see FIG. 5) ). Hereinafter, these three systems
will be described.
[0009]
FIG. 1 is a view schematically showing the configuration of a test signal reproduction system 100
provided in the signal processing apparatus of the present embodiment. As shown in the figure,
the test signal reproduction system 100 detects the sound reproduction unit 11, the volume unit
12, the DAC unit 13, the speaker 14, the microphone 15, the ADC unit 16, the filter processing
unit 17, and A unit 18 and a control unit 19 are provided.
[0010]
Under the control of the control unit 19, the sound reproduction unit 11 generates a test sound
signal such as a sweep signal, a tone burst signal, a TSP signal, or a white noise signal, and
outputs it as a test signal. The volume unit 12 adjusts and outputs the volume of the test signal
input from the sound reproduction unit 11 according to the control of the control unit 19. The
DAC unit 13 converts the test signal input from the volume unit 12 through the signal processing
unit 20 into an analog signal, and outputs the analog signal to the speaker 14.
[0011]
The speaker 14 converts the analog signal input from the DAC unit 13 into physical vibration
and outputs it as sound in the space in which the signal processing device is placed. The
microphone 15 picks up the sound transmitted in the space where the signal processing device is
placed. Specifically, the microphone 15 picks up the sound of the test signal output from the
speaker 14 into the space, and outputs it to the ADC unit 16 as a sound collection signal. The
sampling frequency on the microphone 15 side is assumed to be equal to or higher than the
sampling frequency on the speaker 14 side. The microphone 15 may be configured by a
detachable external connection (external) microphone. When the microphone 15 is an externally
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connected microphone, the distance from the speaker 14 is fixed, for example, at a listening
point of the user's listening environment.
[0012]
The ADC unit 16 converts the collected sound signal collected by the microphone 15 into a
digital signal and outputs the digital signal to the filter processing unit 17.
[0013]
The filter processing unit 17 receives the test signal after volume adjustment output from the
volume unit 12 and the sound collection signal from the ADC unit 16.
The filter processing unit 17 is a linear adaptive filter that adaptively learns a filter coefficient
that suppresses an echo component (a component in which a test signal output from the speaker
14 gets into the microphone 15 through space) included in the collected signal. Using this, a
filter process is performed to suppress the echo component. Further, the filter processing unit 17
outputs the collected sound signal after the filtering process to the detecting unit 18 as a signal
after the filtering process.
[0014]
The detection unit 18 measures the level of an echo component (hereinafter referred to as a
residual echo component level) included in the filtered signal input from the filtering unit 17.
Further, when detecting that the echo component level has changed discontinuously based on
the amount of change of the residual echo component level between the volume levels, the
detection unit 18 outputs the detection signal to the control unit 19.
[0015]
Here, with reference to FIG.2 and FIG.3, the detection operation | movement of the discontinuous
change in the detection part 18 is demonstrated. FIG. 2 is a diagram showing an example of the
signal after filter processing outputted from the filter processing unit 17, and an echo with the
passage of time when the volume level of the volume unit 12 is small volume, medium volume
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and high volume. It represents the suppression state of the component. Also, the horizontal axis
indicates the passage of time, and the vertical axis indicates the level of the echo component. At
each volume level, it is assumed that the filter coefficients are initialized at time = 0.
[0016]
The filter processing unit 17 learns the filter coefficient so as to suppress the echo component of
the test signal contained in the digital signal, and as shown in FIG. 2, the level of the echo
component decreases with the passage of time. . The detection unit 18 measures the echo
component level included in the filtered signal after a predetermined time when the echo
component suppression effect becomes effective, that is, the level of the remaining echo
component (residual echo component level).
[0017]
FIG. 3 is a diagram showing an example of the residual echo component level, where the
horizontal axis indicates the volume level and the vertical axis indicates the residual echo
component level. In a device that outputs sound (hereinafter referred to as an acoustic device),
when a certain volume is reached, non-linear distortion occurs such as vibration (chatter)
occurring in the device itself or digital clipping. Generally, when the acoustic device is small, it is
known that the volume at which vibration occurs in the acoustic device is smaller than the
volume at which the digital clip occurs. In addition, when the acoustic device is large, it is known
that the volume at which vibration occurs in the acoustic device is larger than the volume at
which the digital clip occurs. The volume of the smaller one is represented by V1 and the volume
of the larger one is represented by V2 in terms of the volume at which vibration occurs in the
acoustic device and the volume at which the digital clip occurs. The residual echo component
levels at the sound volume V1 and the sound volume V2 when the vibration of the acoustic
device and the digital clip occur are, as shown in FIG. It changes continuously.
[0018]
The detection unit 18 detects the occurrence of the discontinuous change (discontinuous change)
at the level of the residual echo component as shown in FIG. 3 and outputs the detection signal to
the control unit 19. Specifically, the detection unit 18 detects (determines) that a discontinuous
change has occurred when the amount of change of the residual echo component level between
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successive sound volume levels exceeds a predetermined threshold, and detects the detection
signal It is output to the control unit 19. The volume at the time of detecting that this
discontinuous change has occurred corresponds to the volume V1 shown in FIG.
[0019]
Returning to FIG. 1, the control unit 19 includes a central processing unit (CPU), a read only
memory (ROM), a random access memory (RAM), and the like, develops a predetermined
program stored in the ROM into the RAM and executes it. Thus, various functions related to the
operation of the signal processing device are realized.
[0020]
Specifically, the control unit 19 controls the sound reproduction unit 11 to cause the sound
reproduction unit 11 to output a test signal.
Further, the control unit 19 increases the volume level of the volume unit 12 stepwise, and
before receiving the detection signal of the occurrence of the discontinuous change from the
detection unit 18 at any volume level, before receiving the detection signal. The set value of the
volume level is acquired (specified) as the upper limit value of the volume level at which nonlinear distortion does not occur.
[0021]
Next, the frequency characteristic measurement system 200 will be described. FIG. 4 is a view
schematically showing the configuration of a frequency characteristic measurement system 200
provided in the signal processing apparatus of the present embodiment. As shown in the figure,
the frequency characteristic measurement system 200 includes a frequency characteristic
measurement unit 21 in addition to the sound reproduction unit 11, the volume unit 12, the DAC
unit 13, the speaker 14, the microphone 15, the ADC unit 16 and the control unit 19 described
above. , And the inverse characteristic calculation unit 22 and the inverse characteristic storage
unit 23. The functions of the frequency characteristic measurement system 200 will be described
only for the sound reproduction unit 11, the volume unit 12, the DAC unit 13, the speaker 14,
the microphone 15, the ADC unit 16, and the control unit 19.
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[0022]
The control unit 19 sets the volume level equal to or less than the upper limit value to the
volume value on the basis of the upper limit value of the volume level in which the nonlinear
distortion specified in the operation of the test signal reproduction system 100 does not occur. A
signal to be instructed is output to the characteristic measurement unit 21. In the frequency
characteristic measurement system 200 as well, the control unit 19 controls the sound
reproducing unit 11 to cause the sound reproducing unit 11 to output a test signal.
[0023]
The characteristic measurement unit 21 receives the test signal output from the volume unit 12
and the sound collection signal output from the ADC unit 16. The characteristic measuring unit
21 measures the frequency characteristic of the speaker 14 based on the difference value
between the test signal and the collected signal, and outputs the measured frequency
characteristic to the inverse characteristic calculating unit 22.
[0024]
The inverse characteristic calculation unit 22 calculates the inverse characteristic of the
frequency characteristic measured by the characteristic measurement unit 21 using a
predetermined arithmetic expression, and stores the calculated inverse characteristic in the
inverse characteristic storage unit 23. The inverse characteristic storage unit 23 is a writable
non-volatile storage medium, and holds the inverse characteristic calculated by the inverse
characteristic calculation unit 22.
[0025]
Next, the content reproduction system 300 will be described. FIG. 5 is a view schematically
showing the configuration of a content reproduction system 300 provided in the signal
processing device of this embodiment. As shown in the figure, the content reproduction system
300 has a frequency characteristic correction unit 31 in addition to the sound reproduction unit
11, the volume unit 12, the DAC unit 13, the speaker 14 and the inverse characteristic storage
unit 23 described above. The functions of the content reproduction system 300 will be described
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only for the sound reproduction unit 11, the volume unit 12, the DAC unit 13, the speaker 14,
and the inverse characteristic storage unit 23.
[0026]
The sound reproduction unit 11 reproduces contents such as audio data and audio data stored in
a storage medium (not shown) in accordance with an operation signal input via the operation
input unit (not shown), and the volume of the sound signal is calculated. Output to The volume
unit 12 adjusts the volume level in accordance with the operation signal input via the operation
input unit (not shown), and outputs the acoustic signal after the volume adjustment to the
characteristic correction unit 31.
[0027]
The characteristic correction unit 31 reads the inverse characteristic stored in the inverse
characteristic storage unit 23, corrects the acoustic signal after the volume adjustment with the
filter having the inverse characteristic, and outputs the acoustic signal to the DAC unit 13. Then,
the DAC unit 13 converts the acoustic signal filtered by the characteristic correction unit 31 into
an analog signal and outputs the analog signal to the speaker 14, whereby the sound of the
acoustic signal is output from the speaker 14.
[0028]
As described above, since the inverse characteristic calculated by the frequency characteristic
measurement system 200 is derived based on the frequency characteristic measured at the
volume level at which non-linear distortion does not occur, it is assumed that the acquired
frequency characteristic is accurate. Become. Therefore, by correcting the acoustic signal using
the inverse characteristic calculated from the frequency characteristic, it is possible to achieve
high sound quality of the acoustic signal.
[0029]
The operation of the signal processing apparatus according to this embodiment will be described
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below with reference to FIG. Here, FIG. 6 is a flowchart showing the procedure of the reverse
characteristic setting process performed by the signal processing device of the present
embodiment.
[0030]
First, the arrangement positions of the speaker 14 and the microphone 15 are determined as
preparation for this process (step S11). Here, in the case of a configuration in which the
arrangement position can be adjusted, for example, the speaker 14 is externally attached, the
speaker 14 is placed at a position (for example, 5.1 ch arrangement etc.) according to the user's
listening environment. Deploy. Also, in the case of a configuration in which the arrangement
position can be adjusted, for example, the microphone 15 is externally attached, the microphone
15 is arranged at the listening point in the listening environment. When the speaker 14 and the
microphone 15 are built in the signal processing apparatus, the arrangement positions of the
speaker 14 and the microphone 15 are fixed and thus used as they are.
[0031]
When the control unit 19 sets the value of the parameter n for identifying each volume level to
the initial value “0” (step S12), the volume level V (n) determined by the value of n (n = 0) It
sets to the part 12 (step S13). Here, the value of the initial value V (0) of the volume level is not
particularly limited, and may be, for example, “0”. The parameter n is an integer greater than
or equal to 0, and the volume level V (n) increases as the value of n increases by one. The degree
of the volume level to be increased is not particularly limited.
[0032]
Next, the control unit 19 controls the sound reproducing unit 11 to output a test signal (step
S14). Along with this, the microphone 15 picks up echo sound in the space of the test signal
outputted in step S14, and outputs the sound pickup result to the filter processing unit 17
through the ADC unit 16. Further, the filter processing unit 17 performs filter processing for
suppressing an echo component included in the collected sound signal from the ADC unit 16, and
outputs a filtered signal as a processing result to the detection unit 18.
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[0033]
The detection unit 18 measures the level of the residual echo component included in the filtered
signal input from the filtering unit 17 (step S15). Next, the detection unit 18 determines whether
the residual echo component level changes discontinuously based on the residual echo
component level measured at each volume level (step S16). When the discontinuous change is
not detected, the detection unit 18 outputs a signal (non-detection signal) indicating nondetection to the filter processing unit 17 (Step S16; No). In the present process, the non-detection
signal is output to the control unit 19 when a discontinuous change is not detected. However, the
present invention is not limited to this, and the non-detection signal may not be output.
[0034]
When the control unit 19 receives the non-detection signal from the detection unit 18, the value
of the parameter n is incremented by one (step S17), and the volume of the test signal output
from the speaker 14 is increased by returning to step S13.
[0035]
In addition, when a discontinuous change in the residual echo component level is detected in step
S16, the detection unit 18 outputs a detection signal of the discontinuous change to the filter
processing unit 17 (step S16; Yes).
In this case, the control unit 19 acquires (specifies) the previous volume level V (n-1) as the
upper limit value of the volume level at which non-linear distortion does not occur, and the
volume level V (n-1) (Step S18). Then, the control unit 19 instructs the frequency characteristic
measurement unit 21 to start the frequency characteristic as a function of the frequency
characteristic measurement system 200. In this process, in step S18, the upper limit value of the
sound volume level at which non-linear distortion does not occur is set in the volume unit 12.
However, the present invention is not limited to this. .
[0036]
The frequency characteristic measurement unit 21 measures the frequency characteristic of the
speaker 14 based on the difference value between the test signal from the volume unit 12 and
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the sound collection signal from the ADC unit 16, and the measured frequency characteristic is
inverse characteristic calculation unit It outputs to 22 (step S19). When the inverse characteristic
calculation unit 22 calculates the inverse characteristic of the frequency characteristic measured
in step S19 (step S20), the inverse characteristic calculation unit 22 stores the inverse
characteristic in the inverse characteristic storage unit 23 (step S21), and ends this processing.
[0037]
Then, the content reproduction system 300 corrects the frequency characteristic of the content
(sound signal) using the inverse characteristic stored in step S21, and outputs an acoustic signal
suitable for the frequency characteristic of the speaker 14 from the speaker 14 Do.
[0038]
As described above, according to the signal processing device of the present embodiment, the
output sound from the speaker 14 of the test signal is collected by the microphone 15 while the
volume level of the test signal is gradually increased, and the sound collection is performed. The
residual echo component level is measured from the result of applying echo component
suppression processing to the signal, and a discontinuous change in the level of the echo
component is detected from the amount of change in the residual echo component level between
successive sound volume levels.
Then, the volume level set immediately before the volume level when the discontinuous change is
detected is acquired as the upper limit value of the volume level at which non-linear distortion
does not occur. As a result, the occurrence of non-linear distortion can be detected without
directly analyzing the pulse of the collected signal, and therefore, it is possible to efficiently
specify the upper limit value of the volume level at which non-linear distortion does not occur.
Moreover, since the frequency characteristic of the speaker 14 can be measured in the state
where the volume level equal to or lower than the acquired upper limit value is set in the volume
unit 12, the frequency characteristic of the speaker 14 can be measured more accurately.
Furthermore, since the content (acoustic signal) after the adjustment of the volume level can be
corrected using the filter having the inverse characteristic calculated from the frequency
characteristic, the sound quality of the acoustic signal can be improved. it can.
[0039]
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12
While the embodiments of the present invention have been described above, the above
embodiments are presented as examples, and are not intended to limit the scope of the invention.
The above embodiment can be implemented in other various forms, and various omissions,
replacements, changes, additions, and the like can be made without departing from the scope of
the invention. Moreover, while being included in the range and summary of invention, the said
embodiment and its deformation | transformation are included in the invention described in the
claim, and its equivalent range.
[0040]
For example, in the above embodiment, the test signal after the volume adjustment is performed
by the volume unit 12 is input to the filter processing unit 17. However, the present invention is
not limited to this. It is good also as composition which inputs into 17. Hereinafter, this
configuration will be described as a first modification of the present embodiment.
[0041]
FIG. 7 is a view schematically showing a configuration of a test signal reproduction system 100A
according to the modification 1 of the embodiment. In addition, about the component similar to
the said embodiment, the same code | symbol is provided and description is abbreviate | omitted.
[0042]
As shown in FIG. 7, the test signal reproduction system 100A detects the sound reproduction unit
11, the volume unit 12, the DAC unit 13, the speaker 14, the microphone 15, the ADC unit 16,
the filter processing unit 17A, A unit 18A and a control unit 19 are provided. Further, as a
difference from the configuration shown in FIG. 1, the test signal output from the sound
reproduction unit 11 is configured to be input to the filter processing unit 17A.
[0043]
The filter processing unit 17A receives the test signal output from the sound reproduction unit
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11 and the sound collection signal output from the ADC unit 16. Like the filter processing unit
17, the filter processing unit 17 </ b> A performs a filter process for suppressing an echo
component (a component in which a test signal output from the speaker 14 enters the
microphone 15 through space) included in the collected sound signal. It is applied to the
collected sound signal, and is output to the detection unit 18A as a filtered signal.
[0044]
The detection unit 18A measures the residual echo component level included in the filtered
signal input from the filtering unit 17A. Further, when detecting that the amount of change in the
residual echo component level has changed discontinuously due to the change in the volume
level, the detection unit 18A outputs the detection signal to the control unit 19.
[0045]
Here, the detection operation of the discontinuous change in the detection unit 18A will be
described with reference to FIG. FIG. 8 is a diagram showing an example of the residual echo
component level in the first modification. As in FIG. 3, the horizontal axis indicates the volume
level and the vertical axis indicates the residual echo component level.
[0046]
In the configuration of test signal reproduction system 100A, since the test signal before volume
adjustment is input to filter processing unit 17A, the rate of increase in residual echo component
level with increase in volume level is compared with the rate of increase shown in FIG. Be steep.
Therefore, in the detection unit 18A, the rate of increase (gradient) of the residual echo
component level between successive sound volume levels is used as an index for determining
whether or not it has changed discontinuously, and the rate of increase exceeds a predetermined
threshold. In this case, it detects (determines) that a discontinuous change has occurred, and
outputs the detection signal to the control unit 19.
[0047]
As described above, by adopting the configuration of the first modification, it is possible to
efficiently specify the upper limit value of the volume level at which non-linear distortion does
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not occur, and therefore, the same effect as the signal processing device of the above
embodiment is exhibited. Is possible.
[0048]
In the above embodiment, the measurement of the residual echo component level is collectively
performed for all the frequency components constituting the test signal, but the present
invention is not limited to this. It is good also as composition which measures.
Hereinafter, this configuration will be described as modified example 2 of the above embodiment.
[0049]
FIG. 9 is a view schematically showing a configuration of a test signal reproduction system 100B
according to the second modification of the embodiment. In addition, about the component
similar to the said embodiment, the same code | symbol is provided and description is abbreviate
| omitted.
[0050]
As shown in FIG. 9, the test signal reproduction system 100B detects the sound reproduction unit
11, the volume unit 12, the DAC unit 13, the speaker 14, the microphone 15, the ADC unit 16,
the filter processing unit 17B, and A section 18 B, a control section 19, a filter bank 41, and a
filter bank 42 are included.
[0051]
Here, the filter banks 41 and 42 are arrays of band pass filters, and divide the input signal into
sub bands for each of a plurality of frequency bands.
Specifically, the filter bank 41 divides the test signal output from the volume unit 12 into
predetermined frequency bands, and outputs the divided test signals to the filter processing unit
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17B. The filter bank 42 divides the collected sound signal output from the ADC unit 16 into
predetermined frequency bands and outputs the divided signal to the filter processing unit 17B.
The division unit in the filter banks 41 and 42 is assumed to be the same.
[0052]
The filter processing unit 17B is a filter for suppressing an echo component (a component in
which a test signal output from the speaker 14 enters the microphone 15 through space) for
each of the partial bands divided by the filter bank 41 and the filter bank 42. Processing is
performed, and a filtered signal is output to the detection unit 18B. Further, the detection unit
18B measures the residual echo component level from each of the filtered signals of each partial
band input from the filtering unit 17. When the filter processing unit 17B detects a
discontinuous change in the residual echo component level in any of the partial bands, the filter
processing unit 17B outputs a detection signal to the control unit 19.
[0053]
As described above, according to the configuration of the second modification, since the
discontinuous change of the residual echo component level can be detected in units of a
predetermined frequency band (partial band), the upper limit of the volume level at which nonlinear distortion does not occur Values can be specified in units of frequency bands. When the
configuration of the second modification is used, the residual echo component level may be
measured only for a specific frequency band. In addition, the control unit 19 may continue to
increase the volume level until discontinuous changes in the residual echo component level are
detected in all frequency bands (partial bands).
[0054]
Further, the application destination of the signal processing apparatus of the above embodiment
is not particularly limited, and the present invention can be applied to various devices such as a
mobile phone, a portable or stationary music player, a notebook PC, a tablet terminal, and the
like.
[0055]
100, 100A, 100B test signal reproduction system 200 frequency characteristic measurement
system 300 content reproduction system 11 sound reproduction unit 12 volume unit 13 DAC
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unit 14 speaker 15 microphone 16 ADC unit 17, 17A, 17B filter processing unit 18, 18A, 18B
detection unit 19 control unit 21 characteristic measurement unit 22 inverse characteristic
calculation unit 23 inverse characteristic storage unit 31 characteristic correction unit 41, 42
filter bank
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