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DESCRIPTION JP2015173329

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DESCRIPTION JP2015173329
Abstract: To prevent over-amplitude of a diaphragm while maintaining sound pressure, for
example. An audio signal processing device controls, for example, a volume setting unit that
changes a volume of an audio signal according to control to change a volume, and a level that
controls a level of a predetermined band in an audio signal according to control. And a control
unit. [Selected figure] Figure 2
Audio signal processing apparatus and audio signal processing method
[0001]
The present disclosure relates to an audio signal processing device and an audio signal
processing method.
[0002]
In recent years, a speaker unit having a damperless structure that does not use a mechanical
damper has been proposed for the purpose of improving the structure of the speaker unit and
improving the sound quality of the sound reproduced from the speaker unit.
As an example of such a speaker unit having a damper-less structure, Patent Document 1 and
Patent Document 2 below propose a speaker unit in which a magnetic fluid having viscosity is
filled in a magnetic pole gap formed on the periphery of a voice coil. ing.
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1
[0003]
Japanese Patent Application Publication No. 06-014394
[0004]
JP, 2013-046112, A
[0005]
On the other hand, also in the speaker unit of the above-described damperless structure, it is
required to reproduce an audio signal with high sound pressure.
When the diaphragm is oscillated to generate sound pressure, there is a problem that the
amplitude of the diaphragm exceeds a design limit value and the diaphragm may over-amplify.
[0006]
An object of the present disclosure is to provide an audio signal processing device and an audio
signal processing method that prevent the diaphragm in the speaker unit from over-amplifying
while maintaining the sound pressure of reproduced sound as much as possible. .
[0007]
In order to solve the problems described above, the present disclosure, for example, controls a
volume of an audio signal according to control of changing a volume, and a volume setting unit
for changing a volume of an audio signal according to control. And an audio signal processing
device having a level control unit to control.
[0008]
The present disclosure is, for example, an audio signal processing method in an audio signal
processing apparatus that changes the volume of an audio signal according to control of
changing a volume and controls the level of a predetermined band in the audio signal according
to control. .
[0009]
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According to at least one embodiment, it is possible to prevent over-amplitude of the diaphragm
in the speaker unit while maintaining the sound pressure of reproduced sound as much as
possible.
In addition, the effect described here is not necessarily limited, and may be any effect described
in the present disclosure.
Further, the contents of the present disclosure should not be interpreted as being limited by the
exemplified effects.
[0010]
It is a figure for demonstrating an example of the characteristic of a magnetic fluid speaker unit.
It is a block diagram showing an example of composition of an audio signal reproduction system
in a 1st embodiment of this indication.
It is a figure which shows an example of a structure of a two-dimensional IIR filter. It is a figure
which shows an example of the parameter set to a two-dimensional IIR filter. It is a figure which
shows an example of the characteristic of a two-dimensional IIR filter. It is a flowchart for
demonstrating an example of operation | movement of the audio signal processing apparatus in
1st Embodiment. 7A and 7B are diagrams for explaining an example of the effect of the first
embodiment of the present disclosure. It is a block diagram showing an example of composition
of an audio signal processing device in a 2nd embodiment of this indication. It is a block diagram
for demonstrating an example of a structure of a gain determination part. It is a flowchart for
demonstrating an example of operation | movement of the audio signal processing apparatus in
2nd Embodiment. FIG. 11A shows an example of a change in gain, and FIG. 11B shows an
example of an audio signal.
[0011]
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Hereinafter, a plurality of embodiments of the present disclosure will be described with reference
to the drawings. The description will be made in the following order. <1. First embodiment>
<2. Second embodiment> <3. Modified Examples> The embodiments and the like described below
are preferable specific examples of the present disclosure, and the contents of the present
disclosure are not limited to these embodiments and the like. In the following description,
"sound" includes various sounds such as human voice and music.
[0012]
<1. First embodiment> "an example of a speaker unit" First, an example of a speaker unit in
the present disclosure will be described. A common speaker unit mechanically prevents the
diaphragm from over-amplitude using a damper. Here, the over-amplitude means, for example, a
phenomenon in which the diaphragm oscillates beyond the design limit value. However, although
the speaker unit using the damper can prevent the over-amplitude, the amplitude of the
diaphragm is physically suppressed, so distortion of the sound to be reproduced occurs or the
efficiency of the speaker unit decreases. There is.
[0013]
Therefore, as described above, a speaker unit having a structure (a damperless structure) that
does not use a damper has been proposed. As an example, a speaker unit in which the peripheral
edge of a voice coil is filled with a magnetic fluid (as appropriate, a magnetic fluid speaker unit
Has been proposed). The magnetic fluid is, for example, a dispersion of fine particles of a
magnetic substance in water or oil using a surfactant, and a saturation magnetic flux of, for
example, 30 mT (millithesla) to 40 mT, and a viscosity of 300 cP (centipoise) = 3 Pa · s (pascal ·
second) or less.
[0014]
It is required that a high sound pressure sound can be output to the magnetic fluid speaker unit.
If the volume is raised to cause sound pressure and the diaphragm is made to oscillate, the
amplitude of the diaphragm may exceed the design limit value, and the diaphragm may overamplify. When the diaphragm is over-amplitude, the magnetic fluid may scatter and the speaker
unit may be broken.
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[0015]
FIG. 1 is a view showing an example of the frequency characteristic of a bass reflex type speaker
device using a magnetic fluid speaker unit. In FIG. 1, the horizontal axis represents frequency,
and the vertical axis represents the amplitude of the diaphragm (the amplitude (in units of
millimeter (mm)) from the neutral position of the diaphragm in the positive or negative
direction). A plurality of curves A0, A1, A3... A6 in FIG. 1 correspond to the volume (volume)
respectively, and the volume increases from A0 to A6. In the example shown in FIG. 1, the
magnetic fluid speaker unit is used as a mid-range speaker unit, and the low band is electrically
cut by an HPF (High Pass Filter). Further, the vicinity of 100 Hz is the port resonant frequency of
the bass reflex type speaker device.
[0016]
As shown in FIG. 1, the amplitude of the diaphragm increases as the volume is increased. Then,
when the volume exceeds a certain level (the size of the volume indicated by A5 in the example
of FIG. 1), the amplitude of the diaphragm exceeds the design limit in a band near 200 Hz. That
is, the diaphragm may over-amplify and scattering of the magnetic fluid may occur. As an
assumed technique (not the prior art), it is conceivable to reduce the gain of the amplifier so that
the amplitude of the diaphragm does not exceed the design limit at the maximum volume.
However, in this technology, the sound pressure other than in the band where the diaphragm
over-amplifies is also reduced, and there is a risk that the volume feeling as expected by the user
may be lost. The present disclosure made in view of such a problem will be described.
[0017]
The design limit value of the amplitude of the diaphragm of the speaker unit is obtained, for
example, as follows. First, a combination of an amplifier and a speaker device to be used is
prepared, and a test signal (tone burst signal) is input to the amplifier or the like. Then, the
design limit value of the amplitude of the diaphragm can be obtained by measuring in advance
the amplitude of the diaphragm of the speaker unit, the volume of the amplifier, the gain curve of
the amplitude value and the like using a laser displacement meter or the like. Although the
details will be described later, the center frequency, bandwidth, and gain of the filter for
suppressing the overamplitude are determined so that the amplitude of the diaphragm does not
exceed the design limit value.
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[0018]
[Example of Audio Signal Reproduction System] FIG. 2 is a diagram for explaining an example of
the configuration of the audio signal reproduction system according to the first embodiment. The
audio signal reproduction system 1 includes, for example, an audio signal processing device 10, a
source sound source 150, a power amplifier block 160, a speaker unit 170, and a user interface
unit 180.
[0019]
The audio signal processing apparatus 10 includes, for example, a DSP (Digital Signal Processor)
100 and a system control unit 110 including a microcomputer. The DSP 100 includes, for
example, a two-dimensional IIR (Infinite Impulse Response) filter 101 and a volume setting unit
102. The system control unit 110 includes a memory 111 including a random access memory
(RAM) and a read only memory (ROM). The memory 111 is composed of one or more memories.
[0020]
A source sound source 150 is connected to the audio signal processing device 10, and a digital
audio signal is supplied from the source sound source 150 to the audio signal processing device
10. The digital audio signal supplied from the source sound source 150 is subjected to
predetermined signal processing by the audio signal processing device 10, and the digital audio
signal subjected to the signal processing is output from the audio signal processing device 10. A
digital audio signal supplied from the source sound source 150 to the audio signal processing
device 10 is appropriately abbreviated as an audio signal.
[0021]
A power amplifier block 160 is connected to the audio signal processing apparatus 10, and a
speaker unit 170 is connected to the power amplifier block 160. An audio signal subjected to
signal processing by the audio signal processing device 10 is supplied to the power amplifier
block 160. The power amplifier block 160 performs amplification processing with a
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predetermined amplification factor, and the analog audio signal output from the power amplifier
block 160 operates the speaker unit 170 to reproduce sound. As the speaker unit 170, for
example, the above-described magnetic fluid speaker unit is applied.
[0022]
A user interface unit 180 is connected to the audio signal processing device 10. An operation
signal corresponding to the operation on the user interface unit 180 is generated, and the
operation signal is supplied to the system control unit 110 of the audio signal processing device
10.
[0023]
Each part will be described in detail. The system control unit 110 in the audio signal processing
device 10 controls each unit in the audio signal processing device 10 by executing a program
stored in the memory 111, for example. The memory 111 is also used as a work memory or the
like when executing a program. An operation signal based on an operation of the user interface
unit 180 is supplied to the system control unit 110. The system control unit 110 executes
control based on the operation signal.
[0024]
For example, serial communication is performed between the system control unit 110 and the
DSP 100. The system control unit 110 transfers various setting values for operating the DSP 100
and the filter coefficients of the two-dimensional IIR filter 101 to the DSP 100 using this serial
communication. The filter coefficient or the like is transferred to the DSP 100 at an appropriate
timing, such as when the power is turned on, when switching the mode, when the user interface
unit 180 is operated, or the like.
[0025]
The filter coefficients transferred to the DSP 100 are stored in advance in, for example, the
memory 111. A filter coefficient or the like may be supplied from the outside of the audio signal
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processing device 10 and stored in the memory 111.
[0026]
The DSP 100 executes known signal processing such as equalizing processing to change the
sound quality. In FIG. 2, a two-dimensional IIR filter 101 and a volume setting unit 102 are
shown as functional blocks related to processing in the first embodiment. The two-dimensional
IIR filter 101 functions as a suppression filter that suppresses the level of a predetermined band
in the audio signal supplied from the source sound source 150 as necessary. The predetermined
band is a band in which the speaker unit 170 over-amplifies with a volume equal to or more than
a predetermined level, and is around 200 Hz when the speaker unit 170 is a magnetic fluid
speaker unit. A filter other than the two-dimensional IIR filter may be used as the suppression
filter. The coefficients of the two-dimensional IIR filter 101 are set, for example, under the
control of the system control unit 110.
[0027]
The volume setting unit 102 in the DSP 100 sets the level (gain) of the audio signal so that the
sound is reproduced with the set volume. For example, when a volume is newly set by an
operation on the user interface unit 180, the system control unit 110 transfers a volume value
indicating the volume after the change to the volume setting unit 102. The volume setting unit
102 multiplies the volume value instructed by the system control unit 110 by the audio signal
supplied from the source sound source 150. Thus, the sound is reproduced with the set volume.
[0028]
The control of changing the volume is not limited to the operation by the user, and may be
executed by the automatic volume change function of the device. In conjunction with the control
of changing the volume, the system control unit 110 performs control of setting the coefficient to
the two-dimensional IIR filter 101.
[0029]
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The source sound source 150 is a sound source that supplies an audio signal to the audio signal
processing device 10. The audio signal supplied from the source sound source 150 may be a
signal read from an optical recording medium such as a CD (Compact Disc), a general small
memory, a hard disk drive, etc. A signal obtained via a network such as the Internet May be.
[0030]
The audio signal from the source sound source 150 is, for example, a signal of an R (Right)
channel and is a signal which has passed through an HPF having a predetermined cutoff
frequency. Of course, the audio signal supplied from the source sound source 150 may be a
signal of L (left) channel. When the source sound source 150 corresponds to stereo or multichannel, and an audio signal for each channel is input to the audio signal processing apparatus
10, the same configuration is provided according to each channel.
[0031]
The power amplifier block 160 is configured as, for example, a digital amplifier including an
amplification stage of class D operation. The power amplifier block 160 has, for example, a
configuration including a digital filter, a ΔΣ modulator, a PWM modulator, and an amplification
output unit.
[0032]
An audio signal having a predetermined sampling frequency and quantization bits output from
the audio signal processing device 10 is input to the digital filter. The digital filter performs
digital signal processing such as resampling processing to make the original sampling frequency
a sampling frequency that is a predetermined multiple of the input audio signal. The audio signal
thus subjected to the signal processing by the digital filter is output to the ΔΣ modulator.
[0033]
The ΔΣ modulator includes, for example, an integrator, a quantizer, and the like, and is
configured such that the output of the quantizer is negatively fed back to the input of the
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integrator. With such a configuration, the word length of the quantization bit of the input audio
signal is shortened to a predetermined number of bits. Also, processing called so-called noise
shaping is performed to move the quantization noise component generated at this time to a band
higher than the audio band. This is referred to as ΔΣ modulation, and in this way, as an audio
signal that is Δ と き に modulated, when the audio signal is viewed as an audio signal
waveform, it is 1, 0 according to the time-axis change of the amplitude of the audio signal
waveform. Is a 1-bit pulse train whose density changes. The ΔΣ modulation signal by the 1-bit
pulse train obtained in this manner is input to the PWM modulator.
[0034]
The PWM modulator performs PWM (Pulse Width Modulation) modulation processing on the
input ΔΔ modulation signal. As described above, the ΔΣ modulation signal is a 1-bit pulse
train in which the density of “1” and “0” changes according to the amplitude of the audio
signal waveform. Then, by modulating this signal by PWM, a PWM signal whose pulse width
changes (the amplitude is constant) is generated according to the density of “1” and “0”.
That is, a signal whose pulse width is varied in accordance with the amplitude of the audio signal
waveform corresponding to the ΔΣ modulation signal is obtained.
[0035]
The PWM signal output from the PWM modulator is input to the amplification output unit. As is
well known, the amplification output unit comprises a switching amplification circuit for
switching and amplifying a PWM signal, and a low pass filter for converting the amplification
output into an audio signal waveform. The switching amplifier circuit includes, for example, an Nchannel power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) capable of switching
at high voltage. Also, as a low pass filter, as is well known, an LC low pass filter formed by
including an inductor and a capacitor is adopted.
[0036]
In the amplification output unit, first, the switching amplification circuit performs switching
amplification on the PWM signal input from the PWM modulator, and causes the low-pass filter
to pass the amplification signal. As a result, a drive current of an audio signal waveform flows in
the speaker unit 170, and for example, audio is output from the speaker unit 170.
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[0037]
The power amplifier block 160 is not limited to a digital amplifier having an amplification stage
of class D operation, and may be an amplifier having amplification stages of other operations
(class B, class AB, etc.). Also, a D / A (Digital to Analog) converter may be provided between the
DSP 100 and the power amplifier block 160 to be an amplifier for analog audio signal input.
[0038]
The speaker unit 170 is configured as, for example, a magnetic fluid speaker unit that reproduces
a mid range. The speaker device is configured by a plurality of speaker units including the
speaker unit 170. For example, a speaker device is configured by attaching a speaker unit for
woofer, a speaker unit for subwoofer, a speaker unit for mid-range, and a speaker unit for
tweeter to an enclosure.
[0039]
In addition, the structure of each speaker unit which comprises a speaker apparatus does not
need to be the same. For example, a speaker unit having a mechanical damper may be used as a
speaker unit for woofer and a speaker unit for subwoofer, and a magnetic fluid speaker unit may
be used as a speaker unit for mid-range and a speaker unit for tweeter . Also, the bands of sound
reproduced by the individual speaker units may overlap.
[0040]
The user interface unit 180 is an operator such as a button or a dial for the user to operate the
audio signal processing apparatus 10. The user interface unit 180 includes, for example, an
operator for changing a volume. The user interface unit 180 may be a remote control device for
remotely operating the audio signal processing device 10. The user interface unit 180 may
include a display unit. On the display unit, a reproduction state of sound by the audio signal
processing system may be displayed. The display unit may be configured as a touch panel.
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[0041]
The user interface unit 180 generates an operation signal according to the operation. The
operation signal is supplied to the system control unit 110. The system control unit 110 that has
received the operation signal controls each unit of the audio signal processing device 10 so that
the function corresponding to the operation is performed.
[0042]
Heretofore, an example of the audio signal reproduction system including the audio signal
processing device has been described. The configuration shown in FIG. 2 is an example, and
configurations and functional blocks different from the illustrated configuration may be added as
appropriate.
[0043]
[About Two-Dimensional IIR Filter] FIG. 3 shows an example of the configuration of the twodimensional IIR filter 101. As shown in FIG. The two-dimensional IIR filter 101 includes a
multiplier 120, a multiplier 121, a multiplier 122, a multiplier 123, and a multiplier 124. Further,
the two-dimensional IIR filter 101 has a delay element 130, a delay element 131, a delay element
132, and a delay element 133.
[0044]
The multiplier 120 multiplies the input signal x (n) by the coefficient a0. The delay element 130
delays the input signal x (n) for a predetermined period, and the delay element 131 further
delays the signal delayed by the delay element 130 for a predetermined period. The multiplier
121 multiplies the signal output from the delay element 130 by the coefficient a1. The multiplier
122 multiplies the signal output from the delay element 131 by the coefficient a2.
[0045]
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The delay element 132 delays the output signal y (n) for a predetermined period, and the delay
element 133 further delays the signal delayed by the delay element 132 for a predetermined
period. The multiplier 123 multiplies the signal output from the delay element 132 by the
coefficient b1. The multiplier 124 multiplies the signal output from the delay element 133 by the
coefficient b2. The adder 135 adds and outputs the signals output from the respective
multipliers. The coefficients (coefficient a0, coefficient a1, coefficient a2, coefficient b1, and
coefficient b2) of each multiplier are set by control of the system control unit 110, for example.
[0046]
The parameters of the two-dimensional IIR filter 101 are determined so that the amplitude of the
diaphragm of the speaker unit 170 does not exceed the design limit value and does not exceed
the amplitude. The parameters of the two-dimensional IIR filter 101 include the center frequency
f0, the bandwidth Q, and the gain (cut gain). Here, as an example, the center frequency f0 is set
to 200 Hz (a band in which the diaphragm of the speaker unit 170 may over-amplify with a
certain volume or more), and the bandwidth Q is set to 2. The gain is set according to the volume.
[0047]
FIG. 4 shows an example of parameters set in the two-dimensional IIR filter 101. The parameters
illustrated in FIG. 4 are stored in the memory 111 as a table, for example. Parameters may be
supplied from an external device of the audio signal processing device 10 and stored.
[0048]
In the example of FIG. 4, the maximum signal level of the audio signal supplied from the source
sound source 150 is 0 dB (decibel), and the level L5, the level L4, the level L3,. Level L0 and
volume levels are divided into six levels. Each step of the volume level is, for example, 2 dB.
Parameters of the two-dimensional IIR filter 101 are set corresponding to each volume level. The
parameters are, for example, the center frequency of the two-dimensional IIR filter 101, the
bandwidth, the gain, and the coefficient set to each multiplier. The example of FIG. 4 is an
example in which the amplitude of the diaphragm falls within the design limit value range in the
range where the volume level is smaller than the level L0.
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[0049]
In the example of FIG. 4, a coefficient according to the sampling frequency fs of the audio signal
is set. Thereby, an appropriate coefficient can be set according to the sampling frequency fs of
the audio signal. The coefficient does not necessarily have to be set according to the sampling
frequency fs of the audio signal. For example, the sampling frequency of the original audio signal
may be resampled to a certain frequency, and only the coefficients corresponding to the
resampled frequency may be stored. In addition, appropriate coefficients may be calculated each
time from the sampling frequency of the audio signal, the center frequency of the twodimensional IIR filter 101, the bandwidth, and the gain. Furthermore, only the reference
coefficient may be held and the coefficient may be corrected.
[0050]
For example, at the volume level L5 (range larger than MAX (0 db)-2.0 dB) which is the level of
the largest volume, the center frequency is 200 Hz, the bandwidth 2 and the gain -10 dB as
parameters of the two-dimensional IIR filter 101. It is set. That is, the level of the predetermined
band in the audio signal is largely suppressed. When the sampling frequency fs of the digital
audio signal from the source sound source 150 is 48 kHz, the following coefficients are selected
and set. a0=0.986135372 a1=−1.9587752
a2=0.973311277 b1=1.958775195 b2=−0. 95944665
[0051]
At the volume level L4 in which the volume is lowered by one step, the center frequency is 200
Hz, the bandwidth 2 and the gain -8 dB are set as parameters of the two-dimensional IIR filter
101. When the sampling frequency fs of the digital audio signal supplied from the source sound
source 150 is 48 kHz, the following coefficients are selected and set.
a0=0.990265114 a1=−1.96697816 a2=0.977387314
b1=1.966978162 b2=−0. 96765243
[0052]
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At a volume level L0 (a range of MAX (0 db) -10.0 dB or less) where the volume is lowered by 5
steps, a center frequency of 200 Hz and a bandwidth 2 are set as parameters of the twodimensional IIR filter 101. At the volume level L0, the gain is set to 0 dB because the speaker unit
170 does not cause excessive amplitude around 200 Hz. That is, the level of the predetermined
band in the audio signal is not suppressed. When the sampling frequency fs of the digital audio
signal from the source sound source 150 is 48 kHz, the following coefficients are selected and
set. a0 = 1 a1 = −1.98631471 a2 = 0.9869995603 b1 = 1.9863 14709 b2 = −0.9869956
Alternatively, the following coefficients are selected and set so that the audio signal passes
through the two-dimensional IIR filter 101. Be done. a0=1.0 a1=0.0 a2=0.0
b1=0.0 b2=0. 0
[0053]
FIG. 5 schematically shows the frequency characteristics of the two-dimensional IIR filter 101. As
shown in FIG. In the vicinity of 200 Hz, the cut gain amount of the two-dimensional IIR filter 101
is increased as the volume level is increased.
[0054]
As described above, when the volume is larger than the set value (volume level L0 in the abovedescribed example), the level of the volume to be controlled to suppress the level of the
predetermined band in the audio signal is smaller than the set value. There is no control to
suppress the level of a predetermined band in the audio signal. As in the above-described
embodiment, when the volume level is higher than the set value, control may be performed such
that the level of the predetermined band in the audio signal is stepwise reduced according to the
degree of increase.
[0055]
“One Example of Operation of Audio Signal Processing Device” An example of the operation of
the audio signal processing device 10 will be described with reference to FIG. In step ST101, for
example, a volume change operation is performed by the user using the user interface unit 180.
Then, the process proceeds to step ST102.
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[0056]
In step ST102, the volume setting unit 102 is controlled by the system control unit 110 so that
the volume corresponds to the volume change operation. Then, the process proceeds to step
ST103.
[0057]
The control of step ST103 is performed in conjunction with the control of step ST102. In step
ST103, appropriate coefficients of the two-dimensional IIR filter 101 are selected and set. When
the volume after change is larger than the set value, the coefficient of the two-dimensional IIR
filter 101 is set so as to suppress the level of the predetermined band of the audio signal, so that
excessive amplitude of the speaker unit 170 can be prevented. . Furthermore, since the level of
only a predetermined band of the audio signal is suppressed and the levels of the other bands are
not suppressed, the sound pressure can be secured to the maximum. Further, by suppressing the
level of only the predetermined band, it is possible to prevent the user from feeling the
deterioration of the sound quality and the reduction of the volume.
[0058]
In the speaker unit having a mechanical damper, it is not necessary to suppress the level of the
band including 200 Hz in the audio signal. That is, when the speaker apparatus including the
speaker unit 170 reproduces a band including 200 Hz and has a speaker unit having a structure
having a damper, it is possible to prevent the signal level around 200 Hz from being lowered.
[0059]
FIG. 7A shows an example of the amplitude of the diaphragm when the process of the first
embodiment of the present disclosure is not applied. FIG. 7B shows an example of the amplitude
of the diaphragm when the process of the first embodiment of the present disclosure is applied.
The horizontal axis in FIG. 7 indicates time, and the vertical axis indicates the amplitude of the
diaphragm. As apparent from the two figures, by applying the processing of the first embodiment
of the present disclosure, the amplitude of the diaphragm falls within the design limit value
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range, and it is possible to prevent the diaphragm of the speaker unit from over-amplifying. .
Further, since the level of the band other than the band where the diaphragm of the speaker unit
over-amplifies is not suppressed, the sound pressure can be maintained to the maximum.
[0060]
<2. Second Embodiment> Next, a second embodiment will be described. In addition, about the
structure similar to 1st Embodiment, the same referential mark is attached | subjected and the
description regarding the structure is abbreviate | omitted suitably. Further, unless otherwise
noted, the items described in the first embodiment can be applied to the second embodiment.
[0061]
“One Example of Configuration of Audio Signal Reproduction System” FIG. 8 illustrates an
example of a configuration of an audio signal reproduction system according to the second
embodiment. In the second embodiment, the level of the digital audio signal from the source
sound source is detected according to the control of changing the volume. The gain of the twodimensional IIR filter is dynamically controlled according to the detection result.
[0062]
The audio signal reproduction system 2 includes a source sound source 150, an audio signal
processing device 20, a power amplifier block 160, a speaker unit 170, and a user interface unit
180. The audio signal processing device 20 includes a system control unit 110 and a DSP 200.
The DSP 200 includes a two-dimensional IIR filter 101, a volume setting unit 102, and a
detection unit 201. The detection unit 201 includes a volume setting unit 210 and a gain
determination unit 211. Audio data from the source sound source 150 is branched, and one
audio data is input to the two-dimensional IIR filter 101, and the other audio data is input to the
volume setting unit 210 of the detection unit 201.
[0063]
FIG. 9 is a diagram for describing an example of a detailed configuration of the gain
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determination unit 211. The gain determination unit 211 includes a band pass filter (BPF) 220,
an absolute value circuit 221, a peak detection / hold unit 222, and a comparator 223.
[0064]
For example, according to the user's operation to change the volume, the system control unit 110
executes a process to change the volume. The system control unit 110 transfers the volume value
indicating the volume after change to the volume setting unit 102 and the volume setting unit
210. The volume setting unit 210 changes the level of the audio signal by multiplying the audio
signal by the transferred volume value. Similar processing is performed in the volume setting
unit 102 as well. By the processing in the volume setting unit 210, an audio signal similar to the
audio signal supplied from the volume setting unit 102 to the power amplifier block 160 is
generated.
[0065]
The band pass filter 220 extracts a signal of a predetermined band of the digital audio signal
supplied from the volume setting unit 210. The predetermined band is a band in the vicinity
where the diaphragm of the speaker unit may over-amplify with a certain volume or more. The
parameters of the band pass filter 220 are set such that, for example, the center frequency f0 is
200 Hz and the bandwidth Q is 1. The digital audio signal filtered by the band pass filter 220 is
supplied to the absolute value circuit 221.
[0066]
The absolute value circuit 221 takes an absolute value of a digital audio signal having positive
and negative components. The absolute value circuit 221 may be a squaring circuit that squares
the level of the audio signal.
[0067]
The peak detection / hold unit 222 stores the absolute value supplied from the absolute value
circuit 221 as a peak value with a predetermined time constant. The peak detection / hold unit
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222 compares the held peak value with the latest absolute value supplied from the absolute
value circuit 221, and holds the absolute value as a new peak value if the absolute value is large.
Then, the held peak value (peak hold value) is attenuated with a predetermined time constant (for
example, 0.5 seconds (second) as the release time).
[0068]
The comparator 223 compares the peak value supplied from the peak detection / hold unit 222
with the set level. The setting level is a level corresponding to the design limit value of the
amplitude of the diaphragm of the speaker unit 170. If the peak value is larger than the set level,
the DSP 200 calculates a necessary gain according to the amount of the set level being exceeded.
Then, the DSP 200 obtains a coefficient (control value) for realizing the gain obtained by the
calculation. This coefficient is set to the two-dimensional IIR filter 101. The two-dimensional IIR
filter 101 suppresses the level of the signal in a predetermined band of the audio signal as
necessary.
[0069]
The processing in each unit of the gain determination unit 211 is performed periodically, for
example. For example, the absolute value of the level of the signal of a predetermined band in the
audio signal captured at a certain period is obtained. The obtained absolute value is compared
with the peak hold value to determine whether to update the peak value. When the peak value is
updated, the updated peak value is supplied to the comparator 223. When the peak value is not
updated, the peak hold value or a value obtained by attenuating the peak hold value is supplied
to the comparator 223. To be done.
[0070]
“One Example of Operation of Audio Signal Processing Device” An example of the operation of
the audio signal processing device 20 will be described with reference to the flowchart of FIG.
10. In step ST201, a volume change operation is performed by the user. In response to the
volume change operation, the system control unit 110 sets volume values in the volume setting
unit 102 and the volume setting unit 210. Then, the process proceeds to step ST202.
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[0071]
In step ST202, the volume setting unit 210 executes a process of multiplying the audio signal
from the source sound source 150 by the set volume value. As a result, an audio signal similar to
the audio signal supplied from the volume setting unit 102 to the power amplifier block 160 is
generated. Then, the process proceeds to step ST203.
[0072]
The audio signal whose level has been changed by the volume setting unit 210 is supplied to the
band pass filter 220. The band pass filter 220 extracts a predetermined band in the audio signal.
The predetermined band is, for example, a band around 200 Hz in which the diaphragm of the
speaker unit 170 over-amplifies with a certain volume or more. Then, the absolute value circuit
221 takes the absolute value of the level of the audio signal that has passed through the band
pass filter 220. Then, the process proceeds to step ST204.
[0073]
In step ST204, the peak detection / hold unit 222 holds the absolute value supplied from the
absolute value circuit 221 as a peak value with a predetermined time constant (peak hold). Then,
the process proceeds to step ST205.
[0074]
At step ST205, it is determined whether the latest absolute value exceeds the peak value held by
the peak detection / hold unit 222 or not. If the latest absolute value exceeds the peak value, the
process proceeds to step ST206.
[0075]
The peak value is updated in step ST206. The peak detection / hold unit 222 holds the updated
peak value.
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[0076]
If the latest absolute value is less than the peak value in step ST205, the process proceeds to step
ST207. At step ST207, the comparator 223 determines whether the peak value is larger than the
set level. Then, when the peak value is larger than the set level, the coefficient of the twodimensional IIR filter 101 is set so as to suppress the level of the predetermined band in the
digital audio signal.
[0077]
FIG. 11A shows changes in gain of the two-dimensional IIR filter 101 when the processing of the
second embodiment is applied, and FIG. 11B shows an actual audio signal. The horizontal
direction of FIGS. 11A and 11B indicates the passage of time. The vertical axis in FIG. 11A
indicates the gain size, and the vertical axis in FIG. 11B indicates the level of the audio signal. As
is apparent from FIGS. 11A and 11B, the gain of the two-dimensional IIR filter 101 can be
dynamically changed.
[0078]
As described above, in the second embodiment, only in the case where the level obtained by
multiplying the source signal by the volume value exceeds the over-amplitude level in the area
where the diaphragm may over-amplify, the band is immediately performed. To suppress the
signal level of This can prevent the diaphragm from being over-amplitude. Furthermore, since the
signal level is not suppressed in a band other than the band in which the diaphragm may overamplify, the sound pressure can be maintained to the maximum while preventing the diaphragm
from over-amplifying.
[0079]
<3. Modifications> Although the embodiment of the present disclosure has been specifically
described above, the present disclosure is not limited to the above-described embodiment, and
various modifications based on the technical idea of the present disclosure are possible.
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[0080]
In the above description, the magnetic fluid speaker unit is described as an example, but a
speaker unit to which the present disclosure can be applied is not limited thereto. In addition, the
speaker device using the magnetic fluid speaker unit is not limited to the bass reflex type, and
may be another type (for example, a closed type). Furthermore, the present disclosure can be
applied to the prevention of abnormal noise (chatter noise) of the speaker unit. For example, the
same effect as the present disclosure can be obtained by using a suppression filter according to
the resonance frequency and volume at which chatter noise occurs.
[0081]
The audio signal processing device in the present disclosure can be applied to, for example, a
television device, an in-vehicle device, a portable audio player, and a portable device (smart
phone or notebook computer).
[0082]
The present disclosure is not limited to an apparatus, and can be realized by a method, a
program, a system, and the like.
The program may be provided to the user, for example, via a network or via a portable memory
such as an optical disk or semiconductor memory.
[0083]
In addition, the structure and process in embodiment and a modification can be combined
suitably in the range which technical contradiction does not arise. The order of each process in
the illustrated process flow can be changed as appropriate without causing a technical
contradiction.
[0084]
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The present disclosure can also be applied to a so-called cloud system in which the illustrated
process is distributed and processed by a plurality of devices. The present disclosure can be
realized as a system in which the process illustrated in the embodiment and the modification is
performed, and an apparatus in which at least a part of the illustrated process is performed.
[0085]
The present disclosure can also have the following configurations. (1) An audio signal
comprising: a volume setting unit that changes a volume of an audio signal according to control
to change a volume; and a level control unit that controls a level of a predetermined band in the
audio signal according to the control. Processing unit. (2) The audio signal processing device
according to (1), wherein the level control unit is configured to suppress the level of the
predetermined band in the audio signal when the volume after the change is larger than a set
value. . (3) The level control unit is configured to stepwise suppress the level of the
predetermined band in the audio signal in accordance with the degree to which the volume after
the change is larger than the set value. Audio signal processing apparatus as described. (4) The
level control unit is configured not to change the level of the predetermined band in the audio
signal when the volume after the change is smaller than the set value. An audio signal processing
device according to any one of the preceding claims. (5) A detection unit for detecting the level of
the predetermined band in the audio signal, wherein the level control unit controls the level of
the predetermined band in the audio signal according to the detection result by the detection
unit. The audio signal processing device according to (1), wherein (6) The detection unit includes:
a second volume setting unit that changes a volume of an audio signal according to control to
change the volume; and the predetermined of the audio signal output from the second volume
setting unit. A filter for passing a band, a peak value of the level of the audio signal passed
through the filter is detected, the peak value is held with a predetermined time constant, and the
latest peak value is larger than the held peak value. The audio signal processing device according
to (5), including: a peak holding unit that updates the peak value; and a control value setting unit
that sets a control value according to the peak value held by the peak holding unit. (7) The audio
signal processing device according to any one of (1) to (6), wherein the predetermined band is a
band in which a speaker unit that reproduces the audio signal over-amplifies when the volume
becomes a certain level or more. (8) The audio signal processing device according to (7), wherein
the speaker unit has a damperless structure. (9) The audio signal processing device according to
(8), wherein the speaker unit is a speaker unit in which magnetic fluid is used at the periphery of
a voice coil, and the predetermined band is a band around 200 Hz (hertz).
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(10) An audio signal processing method in an audio signal processing device, which changes a
volume of an audio signal according to control of changing a volume, and controls a level of a
predetermined band in the audio signal according to the control.
[0086]
1, 2 ... audio signal reproduction system 10, 20 ... audio signal processing device 100, 200 ... DSP
101 ... two-dimensional IIR filter 102 ... volume setting unit 110 ... system control unit 170 ...
speaker unit 201 ... detection unit 211 ... gain determination unit
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