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DESCRIPTION JP2008172612

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DESCRIPTION JP2008172612
To set a filter coefficient for suppressing an echo. SOLUTION: A filter coefficient initial setting
unit which sets a predetermined filter coefficient to first and second FIR filters when an echo
preventing apparatus is activated, and an output from the first FIR filter to an AD converter by
generating a first signal. A response signal acquiring unit for acquiring a second response signal
from the output of the second FIR filter to the output of the AD converter by acquiring the first
response signal up to the output of the second signal and generating the second signal; To set a
filter coefficient based on the first response signal to the second FIR filter in order to set the first
analog signal as a signal obtained by removing or attenuating the first analog signal from a signal
obtained by combining the first analog signal and the third analog signal And a filter coefficient
setting unit configured to set a filter coefficient based on the second response signal in the first
FIR filter. [Selected figure] Figure 1
Filter coefficient setting device and program
[0001]
The present invention relates to a filter coefficient setting device and program.
[0002]
In recent years, for example, in communication devices such as mobile phones and hands-free
phones to which an earphone microphone is connected, an echo preventing device is
incorporated to prevent an echo caused by acoustic coupling from a speaker to the microphone
or electrical reflection on a circuit. There is something that is being done.
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[0003]
For example, Patent Document 1 discloses an echo preventing apparatus that cancels an echo
with high accuracy using digital processing.
FIG. 8 is a diagram showing an example of the echo preventing apparatus using the DSP 100. As
shown in FIG.
As shown in the figure, an analog signal indicating a voice transmitted from the other party by a
mobile phone or the like is input to an AD converter 101. Then, the signals digitally converted by
the AD converter 101 are subjected to convolution processing by the FIR filters 102 and 103 in
the DSP 100 based on the respective filter coefficients and output. The signal output from the
FIR filter 102 is input to the DA converter 104. Then, the signal analog-converted by the DA
converter 104 is output to the earphone microphone via the input / output terminal 105 and is
input to one terminal of the differential amplifier circuit 106. Also, the signal output from the FIR
filter 103 is input to the DA converter 107. Then, the signal output from the DA converter 107 is
input to the other terminal of the differential amplifier circuit 106.
[0004]
The signal output from the differential amplifier circuit 106 is converted to a digital signal by the
AD converter 108 and input to the DSP 100. Then, the digital signal is output from the DSP 100,
converted into an analog signal by the DA converter 109, and output as an output signal of the
echo preventing device.
[0005]
Here, the DSP 100 obtains an impulse response from the DA converter 104 to the AD converter
108 by the output of the AD converter 108 when outputting an impulse to the DA converter 104.
Further, the DSP 100 obtains an impulse response from the DA converter 107 to the AD
converter 108 by the output of the AD converter 108 when outputting an impulse to the DA
converter 107. Then, by appropriately setting the filter coefficients of the FIR filters 102 and 103
based on these impulse responses, echo can be canceled with high accuracy. UnexaminedJapanese-Patent No. 2006-304260
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[0006]
By the way, at the start of the echo preventing apparatus, the filter coefficients of the FIR filters
102 and 103 have indefinite values. Therefore, echo cancellation is not performed until the
appropriate filter coefficients are set in the FIR filters 102 and 103 after acquisition of the
impulse response is performed according to an instruction from the user, and an unpleasant echo
is transmitted to the other party. It will be done. Furthermore, since the user of the echo
prevention device can not recognize that an unpleasant echo is transmitted to the other party,
the user does not notice that the impulse response has to be acquired, and the unpleasant echo is
not It may continue to be sent.
[0007]
Then, this invention aims at providing the filter coefficient setting apparatus and program which
can set the filter coefficient which suppresses an echo.
[0008]
A filter coefficient setting device according to the present invention for solving the abovementioned problems receives a first digital signal, a first FIR filter for outputting a second digital
signal, and the first digital signal together with the first FIR filter, A second FIR filter that outputs
a third digital signal, a first DA converter that converts the second digital signal into a first analog
signal and outputs the first analog signal, and a third that converts the third digital signal into a
second analog signal and outputs the second analog signal The second analog signal from a 2DA
converter, an input / output terminal to which the first analog signal is output or a third analog
signal is input, and a signal obtained by combining the first analog signal and the third analog
signal A subtractor for outputting a fourth analog signal from which the subtracter is subtracted,
and the analog signal output from the subtractor circuit into a digital signal, A filter coefficient
setting device for setting a filter coefficient of an echo preventing device including: a power AD
converter, wherein when the echo preventing device is activated, a predetermined filter
coefficient is set in the first and second FIR filters A filter coefficient initial setting unit and a first
signal are generated to obtain a first response signal from an output of the first FIR filter to an
output of the AD converter, and a second signal is generated to generate the second FIR filter A
response signal acquisition unit for acquiring a second response signal from the output of the AD
converter to the output of the AD converter; and a signal obtained by combining the fourth
analog signal with the first analog signal and the third analog signal. A filter coefficient based on
the first response signal to obtain a signal from which the signal has been removed or attenuated;
And sets to the FIR filter, and further comprising a filter coefficient setting unit that sets a filter
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coefficient based on the second response signal to said first 1FIR filter.
[0009]
The filter coefficient initial setting unit may set the filter coefficients of the first and second FIR
filters to zero.
[0010]
The filter coefficient initial setting unit may be configured to set the first and second response
signal data corresponding to the first and second response signals when the echo preventing
device is activated. In order to obtain a signal obtained by removing or attenuating the first
analog signal from a signal obtained by combining a fourth analog signal with the first analog
signal and the third analog signal, a filter coefficient based on the first response signal data is
used. When the second FIR filter is set, a filter coefficient based on the second response signal
data is set in the first FIR filter, and the first and second response signal data are not stored in
the memory. A predetermined filter coefficient is set in the first and second FIR filters, and the
response signal acquisition unit is configured to store the first and second response signal data in
the memory. If not 憶 it may be to acquire the first and second response signals.
[0011]
Furthermore, when the response signal acquisition unit acquires the first and second response
signals, the first and second response signal data corresponding to the first and second response
signals are stored in the memory. It can also be done.
[0012]
The filter coefficient setting device may further include a warning output unit that outputs a
warning signal when the first and second response signal data are not stored in the memory.
[0013]
In the program according to the present invention, a first digital signal is input, a first FIR filter
that outputs a second digital signal, and the first digital signal is input together with the first FIR
filter, and a third digital signal is output 2FIR filter, a first DA converter for converting and
outputting the second digital signal to a first analog signal, a second DA converter for converting
and outputting the third digital signal to a second analog signal, and the first analog A fourth
analog signal obtained by subtracting the second analog signal from a signal obtained by
combining an input / output terminal to which a signal is output or a third analog signal is input,
and the first analog signal and the third analog signal A subtracting unit for outputting, and an
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AD converter for converting an analog signal output from the subtracting circuit into a digital
signal and outputting the digital signal; Function of setting a predetermined filter coefficient to
the first and second FIR filters when the echo prevention device is activated, and the first FIR
filter by generating a first signal to a CPU that controls the echo suppression device. Acquiring a
first response signal from the output of the second to the output of the AD converter, and
generating a second signal to obtain a second response signal from the output of the second FIR
filter to the output of the AD converter; A filter coefficient based on the first response signal in
order to convert the fourth analog signal into a signal obtained by removing or attenuating the
first analog signal from a signal obtained by combining the first analog signal and the third
analog signal; Are set to the second FIR filter, and filter coefficients based on the second response
signal are Shall for implementing a function of setting a filter, the.
[0014]
It is possible to provide a filter coefficient setting device, a filter coefficient setting method, and a
program capable of setting a filter coefficient that suppresses echo.
[0015]
== Overall Configuration == FIG. 1 is a block diagram showing an example of an echo preventing
apparatus to which the present invention is applied.
The echo preventing device 1 includes a digital signal processing circuit (DSP: Digital Signal
Processor) 3, AD converters 4 and 5, DA converters 6 to 8, amplification circuits 9 to 11, a
differential amplification circuit 12, and an input / output terminal 13. There is.
Then, outside the echo preventing device 1, an earphone microphone 20 connected to the input /
output terminal 13, a CPU (Central Processing Unit) 25 that centrally controls the echo
preventing device 1, and a memory 26 that can be read and written by the CPU 25. A learning
button 27 and a warning lamp 28 are provided.
The DA converter 6 corresponds to a first DA converter of the present invention, and the DA
converter 7 corresponds to a second DA converter of the present invention.
Also, the differential amplifier circuit 12 corresponds to the subtracting unit of the present
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invention.
[0016]
The earphone microphone 20 has a speaker function of generating voice by vibrating a
diaphragm (not shown) based on a voice signal input from the input / output terminal 13.
In addition, the earphone microphone 20 also has a microphone function of generating a voice
signal by converting the vibration of the eardrum when the person wearing the earphone
microphone 20 emits a voice to the vibration of the diaphragm.
The earphone microphone 20 is a known technique and is described, for example, in Japanese
Patent Application Laid-Open No. 2003-9272.
Then, an audio signal (third analog signal) generated by the earphone microphone 20 is input to
the echo preventing device 1 through the input / output terminal 13.
Further, the signal output to the earphone microphone 20 via the input / output terminal 13 is
reflected and input from the input / output terminal 13 to the echo preventing device 1. Here,
the signal reflected is, for example, a signal returned through the earphone microphone 20 or a
sound output from the earphone microphone 20 reflected in the ear, and the reflected sound is
converted into an audio signal by the earphone microphone 20. It is a converted signal or the
like. The input / output terminal 13 does not exclusively input / output the output signal and the
input signal. For example, the input / output terminal 13 may input / output the output signal
and the input signal simultaneously.
[0017]
The CPU 25 executes the program stored in the memory 26 to centrally control the echo
preventing apparatus 1. For example, when detecting the power-on for operating the echo
preventing apparatus 1, the CPU 25 outputs an instruction signal for executing a filter coefficient
setting process described later to the DSP 3. Also, for example, when a reset signal for resetting
the echo preventing device 1 is input, the CPU 25 can output the above-mentioned instruction
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signal to the DSP 3.
[0018]
The memory 26 is a non-volatile writable storage area such as a flash memory, which is a type of
EEPROM (Electronically Erasable and Programmable Read Only Memory), and controls the echo
preventing device 1 in addition to the program executed by the CPU 25. Stores various data
required for FIG. 2 is a diagram showing part of the storage unit of the memory 26. As shown in
FIG. The memory 26 is provided with an acquisition flag storage unit 61 and an impulse
response storage unit 62. The acquisition flag storage unit 61 stores an acquisition flag
indicating whether or not an impulse response described later has been acquired in the echo
preventing apparatus 1. In the present embodiment, “1” is set in the acquisition flag when the
impulse response has been acquired, and “0” is set in the acquisition flag when the impulse
response has not been acquired yet. The impulse response storage unit 62 stores data according
to the impulse response acquired by the echo preventing device 1.
[0019]
The learning button 27 is for transmitting to the CPU 25 an instruction to cause the echo
preventing device 1 to acquire an impulse response.
[0020]
The warning lamp 28 is a light emitting device configured of an LED (Light Emitting Diode) or
the like, and lights up or blinks under the control of the CPU 25.
For example, if the impulse response has not been acquired by the echo protection device 1, the
warning lamp 28 can be turned on to prompt acquisition of the impulse response. The warning
lamp 28 can be used not only for warning when an impulse response is not obtained, but also for
notification of arrival of a call or an e-mail.
[0021]
The DSP 3 is configured to include input terminals 30 and 31, output terminals 32 to 34, a DSP
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core 40, a random access memory (RAM) 41, and a read only memory (ROM) 42. The DSP 3 also
includes FIR filters 50 and 51. These FIR filters 50 and 51 are realized by the DSP core 40
executing a program stored in the RAM 41 or the ROM 42. The filter coefficients of the FIR filters
50 and 51 are stored in the RAM 41. Here, the FIR filter 50 corresponds to a first FIR filter of the
present invention, and the FIR filter 51 corresponds to a second FIR filter of the present
invention. The FIR filters 50 and 51 can also be realized by hardware.
[0022]
For example, an audio signal is input to the AD converter 4. Then, the AD converter 4 inputs a
digital signal (first digital signal) obtained by analog-to-digital conversion processing of the audio
signal to the DSP 3 through the input terminal 30.
[0023]
The digital signal input to the DSP 3 is input to the FIR filters 50 and 51, respectively. The FIR
filter 50 outputs a digital signal (second digital signal) obtained by subjecting the input digital
signal to convolution processing based on the filter coefficient of the FIR filter 50 to the output
terminal 32. At the same time, the FIR filter 51 outputs to the output terminal 33 a digital signal
(third digital signal) obtained by subjecting the input digital signal to convolution processing
based on the filter coefficient of the FIR filter 51.
[0024]
An output signal from the FIR filter 50 is input to the DA converter 6 via the output terminal 32.
Then, the DA converter 6 outputs, to the amplification circuit 9, an analog signal (first analog
signal) obtained by subjecting the output signal from the FIR filter 50 to digital / analog
conversion processing. The amplifier circuit 9 amplifies and outputs an analog signal at a
predetermined amplification factor.
[0025]
An output signal from the FIR filter 51 is input to the DA converter 7 via the output terminal 33.
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Then, the DA converter 7 outputs to the amplifier circuit 11 an analog signal (second analog
signal) obtained by subjecting the output signal from the FIR filter 51 to digital / analog
conversion processing. The amplifier circuit 11 amplifies the analog signal at a predetermined
amplification factor and outputs the amplified analog signal to the − input terminal of the
differential amplifier circuit 12.
[0026]
A signal obtained by combining the analog signal output from the amplifier circuit 9 and the
analog signal input from the input / output terminal 13 is input to the positive input terminal of
the differential amplifier circuit 12, and the amplifier circuit is input to the negative input
terminal. An analog signal output from 11 is input. Then, the differential amplifier circuit 12
outputs a signal (fourth analog signal) obtained by amplifying the difference between the analog
signal input to the + input terminal and the analog signal input to the − input terminal.
[0027]
The AD converter 5 inputs a digital signal obtained by analog-to-digital conversion processing on
the analog signal from the amplification circuit 10 to the DSP 3 through the input terminal 31.
The digital signal input to the input terminal 31 is output from the output terminal 34. The
digital signal output from the DSP 3 is input to the DA converter 8 through the output terminal
34. Then, the DA converter 8 outputs an analog signal subjected to digital / analog conversion
processing on the digital signal.
[0028]
The DSP core 40 (processor) can execute various processes in the DSP 3 by executing a program
stored in the RAM 41 or the ROM 42. FIG. 3 is a diagram showing a configuration of functional
blocks realized by the DSP core 40 executing a program. The DSP 3 includes a filter coefficient
initial setting unit 65, a warning output unit 66, an impulse response acquisition unit 67, and a
filter coefficient setting unit 68. The processing device configured by the filter coefficient initial
setting unit 65, the warning output unit 66, the impulse response acquisition unit 67, and the
filter coefficient setting unit 68 corresponds to the filter coefficient setting device of the present
invention.
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[0029]
The filter coefficient initial setting unit 65 sets the initial value (predetermined filter coefficient)
of the filter coefficient to the FIR filter 50 or 51 so that the input digital signal is attenuated and
output when the echo preventing device 1 is activated. Set to In the present embodiment, it is
assumed that the initial value of the filter coefficient is zero in all bits. When all the bits of the
filter coefficient are zero, the input digital signal is completely attenuated and output from the
FIR filters 50 and 51 as silence. Further, when the data according to the impulse response is
stored in the impulse response storage unit 62, the filter coefficient initial setting unit 65 sets the
filter coefficients based on the data according to the impulse response in the FIR filters 50 and
51. Do.
[0030]
The warning output unit 66 refers to the acquisition flag storage unit 61 via the CPU 25 when
the echo preventing device 1 is activated, and outputs a warning signal to the CPU 25 when an
impulse response is not obtained. In response to the warning signal from the warning output unit
66, the CPU 25 turns on the warning lamp 28, for example. The warning notification method is
not limited to the lighting of the warning lamp 28, and any method may be used as long as the
user can recognize that an impulse response has not been obtained, such as the output of a
warning sound.
[0031]
The impulse response acquisition unit 67 refers to the acquisition flag storage unit 61 via the
CPU 25 and acquires an impulse response when an impulse response is not acquired.
Specifically, the impulse response acquisition unit 67 outputs an impulse (first signal) from the
output terminal 32 so that an impulse response IR1 '(Z) (first response signal) of the path A
shown by the solid line in FIG. Is acquired from the input terminal 31. Further, the impulse
response acquisition unit 67 outputs an impulse (second signal) from the output terminal 33 to
input an impulse response IR2 '(Z) (second response signal) of the path B shown by the solid line
in FIG. Obtain from 31 Further, the impulse response acquisition unit 67 stores the acquired
impulse response in the impulse response storage unit 62 via the CPU 25. The impulse response
acquisition unit 67 can store not the acquired impulse response itself but data corresponding to
the impulse response in the impulse response storage unit 62. For example, filter coefficients
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based on an impulse response, which are set in the FIR filters 50 and 51, may be stored in the
impulse response storage unit 62.
[0032]
The filter coefficient setting unit 68 sets the filter coefficient of the FIR filter 51 based on the
impulse response IR1 ′ (Z) acquired by the impulse response acquisition unit 67. Also, the filter
coefficient setting unit 68 sets the filter coefficient of the FIR filter 50 based on the impulse
response IR2 ′ (Z) acquired by the impulse response acquisition unit 67.
[0033]
== Principle of Echo Cancellation == Next, the principle of echo cancellation in the echo
preventing device 1 will be described. Here, the impulse response (transfer function) from the
output terminal 32 shown by the broken line in FIG. 1 to the + input terminal of the differential
amplifier circuit 12 is IR1 (Z). Further, an impulse response (transfer function) from an output
terminal 33 indicated by a broken line in FIG. 1 to a − input terminal of the differential amplifier
circuit 12 is IR2 (Z). Further, an impulse response (transfer function) from the rear stage of the
± input terminal of the differential amplifier circuit 12 shown by the broken line in FIG. 1 to the
input terminal 31 is W (Z).
[0034]
At this time, the impulse response (transfer function) IR1 ′ (Z) of the path A indicated by the
solid line in FIG. 1 is IR1 ′ (Z) = IR1 (Z) · W (Z). Further, the impulse response (transfer function)
IR2 '(Z) of the path B indicated by the solid line in FIG. 1 is IR2' (Z) =-IR2 (Z) W (Z). Note that IR2
(Z) is phase-inverted because it is input to the-input terminal of the differential amplifier circuit
12.
[0035]
Now, assuming that the filter coefficient of the FIR filter 50 is −IR2 ′ (Z) obtained by inverting
the phase of IR2 ′ (Z), the characteristic IRall_1 (Z) from the input of the FIR filter 50 to the
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input terminal 31 is IRall_1 (Z) =-IR 2 '(Z) IR 1' (Z) = (-(-IR 2 (Z) W (Z)) (IR 1 (Z) W (Z)) IR 2 (Z) W
(Z) It becomes IR1 (Z) W (Z). Further, assuming that the filter coefficient of the FIR filter 51 is IR1
'(Z), the characteristic IRall2 (Z) from the input of the FIR filter 51 to the input terminal 31 is
IRall2 (Z) = IR1' (Z) IR2 '(Z) ) = IR1 (Z) · W (Z) · (−IR2 (Z) · W (Z)) = IR1 (Z) · W (Z) · (−IR2 (Z)) · W
(Z) = − IRall_1 It becomes (Z).
[0036]
That is, it can be seen that the characteristic IRall_1 (Z) from the input of the FIR filter 50 to the
input terminal 31 and the characteristic IRall_2 (Z) from the input of the FIR filter 51 to the input
terminal 31 mutually cancel each other. As a result, it is understood that the filter coefficient of
the FIR filter 50 may be set to -IR2 '(Z) obtained by inverting IR2' (Z) and the filter coefficient of
the FIR filter 51 may be set to IR1 '(Z).
[0037]
Alternatively, assuming that the filter coefficient of the FIR filter 50 is IR2 ′ (Z), the
characteristic IRall_1 (Z) from the input of the FIR filter 50 to the input terminal 31 is IRall_1 (Z)
= IR2 ′ (Z) · IR1 ′ ( Z) = (-IR2 (Z) .W (Z)). (IR1 (Z) .W (Z)) =-IR2 (Z) .W (Z) .IR1 (Z) .W (Z) .
Further, assuming that the filter coefficient of the FIR filter 51 is −IR1 ′ (Z) obtained by
inverting the phase of IR1 ′ (Z), the characteristic IRall_2 (Z) from the input of the FIR filter 51
to the input terminal 31 is IRall_2 (Z) = -IR1 '(Z) .IR2' (Z) = (-(IR1 (Z) .W (Z))). (-IR2 (Z) .W (Z)) =
IR1 (Z) .W (Z) ) IR2 (Z) W (Z) =-IRall_1 (Z)
[0038]
That is, it can be seen that the characteristic IRall_1 (Z) from the input of the FIR filter 50 to the
input terminal 31 and the characteristic IRall_2 (Z) from the input of the FIR filter 51 to the input
terminal 31 mutually cancel each other. As a result, it is understood that the filter coefficient of
the FIR filter 50 may be set to IR2 '(Z), and the filter coefficient of the FIR filter 51 may be set to IR1' (Z) obtained by inverting IR1 '(Z).
[0039]
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Then, by setting the filter coefficients of the FIR filters 50 and 51 based on the impulse responses
IR1 ′ (Z) and IR2 ′ (Z) as described above, the signal transmitted through the path A in the
differential amplifier circuit 12 can be It becomes possible to cancel out by the signal which
transmits B. As a result, it is possible to prevent an echo when a digital signal is input to the input
terminal 30.
[0040]
Further, as shown in FIG. 1, the impulse response IR1 ′ (Z) is acquired in a state in which the
earphone microphone 20 is connected, and the filter coefficient of the FIR filter 51 is set based
on the IR 1 ′ (Z), Effective echo prevention according to the transfer characteristic of the
earphone microphone 20 is possible. Furthermore, an impulse response IR1 '(Z) is obtained in a
state of being attached to the ear by inserting the connected earphone microphone 20 into the
ear hole or covering the pinna, and based on this IR 1' (Z) By setting the filter coefficient of the
FIR filter 51, it is possible to effectively prevent echo according to the transfer characteristic of
the earphone microphone 20 and the transfer characteristic in the user's ear. The impulse
response IR1 ′ (Z) may be acquired in a state where the earphone microphone 20 is not
connected, and the filter coefficient of the FIR filter 51 may be set based on the IR 1 ′ (Z).
[0041]
== Filter Coefficient Setting Processing == Next, filter coefficient setting processing in the echo
preventing device 1 will be described. FIG. 4 is a flowchart showing an example of the filter
coefficient setting process. First, when the echo preventing apparatus 1 is activated (S401), the
filter coefficient initial setting unit 65 reads the acquisition flag stored in the acquisition flag
storage unit 61 via the CPU 25 (S402).
[0042]
When the acquisition flag read from the acquisition flag storage unit 61 is “1”, that is, when
the impulse response is stored in the impulse response storage unit 62 (S402: 1), the filter
coefficient initial setting unit 65 generates the CPU 25 The impulse responses IR1 '(Z) and IR2'
(Z) stored in the impulse response storage unit 62 are read out via the (S403). Then, the filter
coefficient initial setting unit 65 sets the filter coefficients of the FIR filters 50 and 51 based on
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the impulse responses IR1 ′ (Z) and IR2 ′ (Z) read from the impulse response storage unit 62
(S404). Specifically, for example, −IR 2 ′ (Z) obtained by inverting the phase of the impulse
response IR 2 ′ (Z) is set as the filter coefficient of the FIR filter 50, and the impulse response IR
1 ′ (Z ) Is set.
[0043]
When the acquisition flag read from the acquisition flag storage unit 61 is "0", that is, when the
impulse response is not stored in the impulse response storage unit 62 (S402: 0), the filter
coefficient initial setting unit 65 performs FIR Zero is set as an initial value to all bits of the filter
coefficients of the filters 50 and 51 (S405). Furthermore, the warning output unit 66 turns on
the warning lamp by outputting a warning signal to the CPU 25 (S406).
[0044]
Thereafter, when the CPU 25 is notified that the learning button 27 has been pressed, the
impulse response acquisition unit 67 acquires impulse responses IR1 ′ (Z) and IR2 ′ (Z)
(S407). Then, the filter coefficient setting unit 68 sets the filter coefficients of the FIR filters 50
and 51 based on the impulse responses IR1 ′ (Z) and IR2 ′ (Z) acquired by the impulse
response acquiring unit 67 (S408). Specifically, for example, −IR 2 ′ (Z) obtained by inverting
the phase of the impulse response IR 2 ′ (Z) is set as the filter coefficient of the FIR filter 50,
and the impulse response IR 1 ′ (Z ) Is set. Then, the warning output unit 66 turns off the
warning lamp by outputting a warning cancellation signal indicating that the impulse response
has been acquired to the CPU 25 (S409).
[0045]
Further, the impulse response acquisition unit 67 stores the acquired impulse responses IR1 ′
(Z) and IR2 ′ (Z) in the impulse response storage unit 62 via the CPU 25 (S410), and the
impulse response has already been acquired. An acquisition flag in which “1” is set indicating
that is stored in the acquisition flag storage unit 61 via the CPU 25 (S411).
[0046]
In this embodiment, −IR 2 ′ (Z) obtained by inverting the phase of the impulse response IR 2 ′
(Z) is set as the filter coefficient of the FIR filter 50, and the impulse response IR 1 ′ (Z) is used
as the filter coefficient of the FIR filter 51. The impulse response IR 2 ′ (Z) is set as the filter
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coefficient of the FIR filter 50, and the impulse response IR 1 ′ (Z) is phase-inverted −IR 1 ′
(Z) as the filter coefficient of the FIR filter 51 It may be set.
[0047]
== Example Application of Echo Protection Circuit === An application example of the echo
protection device 1 will now be described.
5 and 6 are schematic views of a mobile phone to which the echo preventing apparatus 1 is
applied.
In the configuration shown in FIG. 5, the echo preventing device 1 is provided outside the mobile
phone 80. Further, in the configuration shown in FIG. 6, the echo preventing device 1 is
incorporated in the mobile phone 85. When the echo preventing device 1 is built in the mobile
phone 85, the learning button 27 and the warning lamp 28 can also be provided in the mobile
phone 85. In this case, the learning button 27 may be provided as a dedicated button or may be
used as a button having another function. Further, the warning lamp 28 can also be dedicated for
displaying a warning regarding an impulse response, and can also be used as a lamp for notifying
of an incoming call or an e-mail.
[0048]
FIG. 7 is a view showing a configuration example of a mobile telephone 85 in which the echo
preventing device 1 is incorporated. The cellular phone 85 includes an echo preventing device 1,
a CPU 25, a memory 26, a learning button 27, a warning lamp 28, an antenna 90, an RF unit 91,
a baseband processing unit 92, a display unit 93, an input unit 94, an AD converter 95, and a DA
converter It comprises 96, a microphone 97, and a speaker 98.
[0049]
The antenna 90 receives an audio signal transmitted to the mobile phone 85. Also, the antenna
90 transmits an audio signal from the RF unit 91. The RF unit 91 performs decoding processing
such as demodulation processing on an audio signal in a predetermined frequency band among
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audio signals received by the antenna 90. Further, the RF unit 91 performs modulation
processing on the audio signal from the baseband processing unit 92, for example, encoding
processing by a TDMA method (Time Division Multiplex Access).
[0050]
The baseband processing unit 92 performs predetermined signal processing on the audio signal
demodulated to the baseband signal by the RF unit 91, and outputs the processed signal to the
CPU 25. Further, the baseband processing unit 92 performs predetermined signal processing on
the audio signal from the CPU 25 and outputs the processed signal to the RF unit 91.
[0051]
The CPU 25 centrally controls the mobile phone 85. The CPU 25 outputs the audio signal to the
DA converter 96 in order to reproduce the audio corresponding to the audio signal from the
baseband processing unit 92 by the speaker 98 or the earphone microphone 20. The CPU 25
also outputs an audio signal from the microphone 97 or the earphone microphone 20 output
from the AD converter 95 to the baseband processing unit 92. Further, for example, when the
mobile telephone 85 is performing packet communication, the CPU 25 outputs a signal to the
display unit 93 to display an image based on the received packet data. In addition, the CPU 25
causes the display unit 93 to display the input data input from the input unit 94, or performs
predetermined processing to transmit the input data by packet communication, and outputs the
data to the baseband processing unit 92. To
[0052]
Further, when the data corresponding to the impulse response is not stored in the impulse
response storage unit 62 when the mobile phone 85 is powered on, the CPU 25 receives a
warning signal from the echo preventing device 1 and turns on the warning lamp 28. Then, when
the learning button 27 is pressed, the CPU 25 causes the echo preventing apparatus 1 to acquire
an impulse response, and causes the FIR filters 50 and 51 to set filter coefficients based on the
impulse response.
[0053]
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The AD converter 95 outputs to the CPU 25 a digital signal obtained by analog-to-digital
conversion processing on the audio signal from the microphone 97 or the earphone microphone
20. The DA converter 96 outputs an analog signal subjected to digital / analog conversion
processing to the audio signal from the CPU 25 to the speaker 98 or the echo preventing device
1. In the present embodiment, when the earphone microphone 20 is connected to the mobile
phone 85, the analog signal from the DA converter 96 is described as being input to the echo
preventing device 1 in the following.
[0054]
The operation of such a portable telephone 85 will be described. The echo preventing apparatus
1 is assumed to have the configuration shown in FIG. First, when the mobile phone 85 is powered
on, the process of FIG. 4 described above is started. Then, filter coefficients are set in FIR filters
50 and 51 based on the impulse response read out from impulse response storage unit 62, or
zero is set as an initial value in all bits of the filter coefficients of FIR filters 50 and 51. Ru.
[0055]
When all bits of the filter coefficients of the FIR filters 50 and 51 are set to zero as an initial
value, the voice signal received by the antenna 90 is subjected to the above-described processing
according to each configuration of the portable telephone 85 and It is output to the AD converter
4 of the echo preventing device 1. The audio signal input to the AD converter 4 is subjected to
analog and digital signal processing by the AD converter 4 to be a digital signal, and input to the
FIR filters 50 and 51 through the input terminal 30. Here, since all bits of the filter coefficients of
the FIR filters 50 and 51 are zero, the digital signal output from the FIR filters 50 and 51 has a
zero level. Therefore, the audio signal transmitted from the other party is not output from the
earphone microphone 20. In addition, since the digital signals output from the FIR filters 50 and
51 are at the zero level, no echo is transmitted to the other party.
[0056]
Then, when the user of the portable telephone 85 notices that the impulse response is not
obtained because the voice is not output from the earphone microphone 20 and the warning
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lamp 28 is lit, the learning button 27 is pressed. Ru. When the learning button 27 is pressed, an
impulse response is acquired in the echo preventing device 1, and filter coefficients are set in the
FIR filters 50 and 51 based on the acquired impulse response.
[0057]
When the filter coefficients of the FIR filters 50 and 51 are set based on the impulse response
read from the impulse response storage unit 62 or the impulse response acquired by the impulse
response acquisition unit 67, the voice received by the antenna 90 The signal is output from the
DA converter 96 to the AD converter 4 of the echo preventing apparatus 1 after the abovedescribed processing according to each configuration of the cellular phone 85 is performed. The
audio signal input to the AD converter 4 is subjected to analog and digital signal processing by
the AD converter 4 to be a digital signal, and input to the FIR filters 50 and 51 through the input
terminal 30. An output signal output from the FIR filter 50 is input to the DA converter 6 via the
output terminal 32. Then, the output signal is subjected to digital / analog conversion processing
by the DA converter 6 to be an analog signal, which is input to the amplifier circuit 9. The analog
signal input to the amplifier circuit 9 is amplified at a predetermined amplification factor and
output. The analog signal from the amplifier circuit 9 is output to the earphone microphone 20
via the input / output terminal 13. As a result, the diaphragm of the earphone microphone 20
vibrates to generate sound. The analog signal from the amplifier circuit 9 is also input to the +
input terminal of the differential amplifier circuit 12.
[0058]
In addition, an output signal output from the FIR filter 51 is input to the DA converter 7 through
the output terminal 33. Then, the output signal is subjected to digital / analog conversion
processing by the DA converter 7 to be an analog signal, which is input to the amplifier circuit
11. The analog signal input to the amplifier circuit 11 is amplified at a predetermined
amplification factor and input to the − input terminal of the differential amplifier circuit 12.
[0059]
The filter coefficients of the FIR filters 50 and 51 are set in accordance with the process
described above. Therefore, in the differential amplifier circuit 12, an analog signal (first analog
signal) output from the amplifier circuit 9 input to the + input terminal and a signal obtained by
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combining the reflection signal of the analog signal by the earphone microphone 20 etc. It can
cancel out by the analog signal (2nd analog signal) from the amplifier circuit 11 input into an
input terminal. As a result, it is possible to prevent an echo when a digital signal is input to the
input terminal 30. Further, an audio signal (third analog signal) by the microphone function of
the earphone microphone 20, an analog signal (first analog signal) from the amplifier circuit 9,
and a signal obtained by combining the reflection signal of the analog signal by the earphone
microphone 20 are superimposed. If the signal (second analog signal) from the FIR filter 51 is
input to the-input terminal, even if the signal is input to the + input terminal of the differential
amplifier circuit 12, an echo is generated from the superimposed signal. It is possible to deduct
the signal which is the cause of (i.e., the analog signal from the amplifier circuit 9 and the
reflected signal of the analog signal).
[0060]
Note that even when the filter coefficient of the FIR filter 51 is set based on the impulse response
IR1 ′ (Z) acquired in the state where the earphone microphone 20 is not connected, the analog
signal (the One analog signal is canceled by the analog signal (second analog signal) output from
the amplifier circuit 11. However, as shown in the present embodiment, the filter coefficient of
the FIR filter 51 is set based on the impulse response IR1 ′ (Z) acquired in a state in which the
earphone microphone 20 is connected. In addition to the output analog signal (first analog
signal), it is possible to cancel the reflection signal of the analog signal by the earphone
microphone 20 or the like, and it is possible to cancel the echo with high accuracy.
[0061]
Although the configuration and operation of the mobile phone 85 in which the echo preventing
apparatus 1 is incorporated have been described, the same applies to a mobile phone 80 to
which the echo preventing apparatus 1 is externally attached.
[0062]
Moreover, in this application example, although the case where the echo preventing apparatus 1
was applied to a mobile telephone was demonstrated, it does not restrict to this.
The echo preventing device 1 is applicable as long as the above-mentioned echo may occur. For
example, the present invention can be applied to an information technology (IT) communication
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device (for example, a PC (Personal Computer) or the like) and a calling device (for example, a
telephone, a transceiver, or an in-vehicle device).
[0063]
Heretofore, an embodiment of the present invention has been described. As described above,
when the echo preventing apparatus 1 is activated, the filter coefficient initial setting unit 65 sets
the filter coefficients (predetermined filter coefficients) that attenuate and output the input
digital signal in the FIR filters 50 and 51. By doing this, the signal level of the echo transmitted to
the other party can be reduced. That is, it becomes possible to suppress the unpleasant echo
transmitted to the other party. In addition, as the signal is attenuated by the FIR filter 50, the
sound output from the earphone microphone 20 is also reduced. Therefore, the user of the
earphone microphone 20 can easily notice that the impulse response has not been acquired, and
the acquisition of the impulse response is prompted.
[0064]
Furthermore, as shown in the present embodiment, the filter coefficient initial setting unit 65 can
set all bits of the filter coefficients of the FIR filters 50 and 51 to zero as an initial value. In this
case, the digital signals input to the FIR filters 50 and 51 are completely attenuated and output
as silence. Therefore, echo is not transmitted to the other party. Further, since the voice
transmitted from the other party is not output at all from the earphone microphone 20, it
becomes easy to notice that the impulse response is not obtained.
[0065]
When the impulse response is stored in the impulse response storage unit 62 when the echo
preventing apparatus 1 is activated, the filter coefficient initial setting unit 65 performs FIR filter
50 based on the impulse response read out from the impulse response storage unit 62. , 51 filter
coefficients are set. That is, after the activation of the echo preventing apparatus 1, appropriate
filter coefficients capable of suppressing echo are set in the FIR filters 50 and 51 based on the
already acquired impulse response, and the echo is unpleasant for the other party. Can be
suppressed.
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[0066]
Further, the impulse response acquisition unit 67 stores the acquired impulse response in the
impulse response storage unit 62, so that when the echo preventing apparatus 1 is activated
next, an appropriate filter coefficient that can suppress an echo is FIR. As a result of being set in
the filters 50 and 51, it is possible to suppress the transmission of an unpleasant echo to the
other side without acquiring the impulse response again.
[0067]
In addition, when the impulse response is not stored in the impulse response storage unit 62, the
warning output unit 66 outputs a warning signal to turn on the warning lamp 28 or the like, so
that the impulse response is not obtained. The user of the earphone microphone 20 can be more
easily understood.
[0068]
The embodiments and application examples described above are for the purpose of facilitating
the understanding of the present invention, and are not for the purpose of limiting and
interpreting the present invention.
The present invention can be modified or improved without departing from the gist thereof, and
the present invention also includes the equivalents thereof.
[0069]
For example, in the present embodiment, the impulse response obtained by generating an
impulse is set as the filter coefficient of the FIR filter, but the signal used to set the filter
coefficient is not limited to the impulse.
For example, the filter coefficients of the FIR filter may be set based on the response signal
obtained when the step signal is generated.
[0070]
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1 is a block diagram showing an example of an echo preventing apparatus to which the present
invention is applied. It is a figure which shows a part of memory | storage part which memory
has. It is a figure which shows the structure of the functional block implement | achieved when
DSP core runs a program. It is a flowchart which shows an example of a filter coefficient setting
process. It is a schematic diagram of the mobile telephone to which the echo prevention
apparatus was connected outside. It is a schematic diagram of the mobile telephone in which the
echo prevention apparatus was incorporated. It is a block diagram which shows an example of a
structure of a mobile telephone. It is a figure which shows the conventional echo prevention
apparatus.
Explanation of sign
[0071]
DESCRIPTION OF SYMBOLS 1 Echo prevention apparatus 3 DSP 4, 5, 95 AD converter 6-8, 96
DA converter 9-11 Amplifier circuit 12 Differential amplifier circuit 20 Earphone microphone 25
CPU 26 Memory 27 Learning button 28 Warning lamp 30, 31 Input terminal 32-31 34 output
terminal 41 RAM 42 ROM 50, 51 FIR filter 61 acquisition flag storage unit 62 impulse response
storage unit 65 filter coefficient initial setting unit 66 warning output unit 67 impulse response
acquisition unit 68 filter coefficient setting unit 80, 85 mobile phone 90 antenna 91 RF unit 92
baseband processing unit 93 display unit 94 input unit 97 microphone 98 speaker
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