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DESCRIPTION JP2010288041

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DESCRIPTION JP2010288041
[Purpose] It is an object of the present invention to provide a “noise cancellation device” which
can prevent generation of loud noise at the time of mute cancellation and can perform noise
cancellation immediately after mute cancellation. A noise cancellation apparatus for combining a
noise cancellation signal generated by adaptive signal processing with an audio signal and
inputting the resultant signal to a speaker via an amplifier and outputting a sound and a noise
cancellation sound according to the audio signal from the speaker. When audio mute is
instructed from the unit, the microphone detection signal e is set to 0 by blocking so that the
microphone detection signal is not input to the adaptive signal processing unit. As a result, the
coefficient of the adaptive filter becomes H (n + 1) = H (n) and is maintained at the muting value,
so that it is possible to prevent the generation of loud noise at the time of releasing the muting.
[Selected figure] Figure 2
Noise cancellation device
[0001]
The present invention relates to a noise cancellation device, and in particular, a noise cancellation
signal generated by adaptive signal processing is combined with an audio signal and input to a
speaker via an amplifier, and a sound corresponding to the audio signal is output from the
speaker. The present invention relates to a noise cancellation device that outputs a noise
cancellation sound according to a noise cancellation signal.
[0002]
10-04-2019
1
In recent years, an active noise control device provided with an adaptive signal processing unit
that performs noise cancellation processing based on the LMS algorithm, Single frequency
Adaptive Notch Filter algorithm, etc. has become widespread.
In the active noise control device, generally, an active noise reduction is realized by generating a
noise cancellation signal by adaptive signal processing so that the noise power at the microphone
installation position (observation point) is minimized. As such an active noise control device,
there is a device in which a speaker for noise cancellation is shared with an audio speaker to
reduce cost. In such a speaker shared noise control device, when the power amplifier is muted
for some reason, for example, when the power amplifier is muted due to the turning on of the
audio mute key, the output of the audio sound from the speaker is stopped simultaneously with
the noise The output of the cancellation sound also stops. When the noise cancellation sound is
not output, the adaptive signal processing unit continues updating the filter coefficients of the
adaptive filter so as to further increase the output from the adaptive filter, and the filter
coefficients are finally diverged. In this state, when the mute is canceled, the filter output
becomes large, and a loud noise (noise cancellation sound) is output from the speaker, causing
discomfort to the user and damaging the power amplifier and the speaker. There is a risk of For
this reason, when mute is detected, a method for stopping adaptive signal processing, forcibly
setting the adaptive filter coefficient to 0, or setting the adaptive filter input to 0 has been
proposed (see Patent Document 1). .
[0003]
Patent 3395273
[0004]
According to the above proposed method, generation of loud noise at mute cancellation can be
prevented, but it is necessary to restart the adaptive filter coefficient from the beginning, and it is
considerable to cancel noise after mute cancellation. There is a problem that takes time.
From the above, it is an object of the present invention to prevent generation of loud noise at the
time of releasing the mute, and to perform noise cancellation immediately after releasing the
mute.
[0005]
10-04-2019
2
According to the present invention, according to the present invention, a noise cancellation signal
generated by adaptive signal processing is combined with an audio signal and input to a speaker
through an amplifier, and a sound corresponding to the audio signal is output from the speaker
and a noise cancellation signal The noise cancellation device outputs noise cancellation sound
according to the mute unit for muting the audio sound, the microphone provided at the point
where the noise cancellation is desired, the detection signal of the microphone, and the reference
signal according to the noise to be canceled An adaptive signal processing unit that performs
adaptive signal processing and outputs a noise cancellation signal; and means for setting the
microphone detection signal input to the adaptive signal processing unit to 0 when audio mute is
instructed from the mute unit. This is achieved by the provided noise cancellation device.
[0006]
According to the present invention, when audio mute is instructed, the microphone detection
signal input to the adaptive signal processing unit is set to 0, whereby the adaptive filter
coefficient is muted even if the adaptive signal processing is continued in the mute state. It can
be maintained at a value, and the divergence of filter coefficients can be prevented.
As a result, according to the present invention, it is possible to prevent generation of large
volume noise at the time of releasing the mute, and it is possible to perform noise cancellation
using the adaptive filter coefficient maintained immediately after releasing the mute.
[0007]
It is a block diagram of the conventional active noise control apparatus which employ | adopted
the LMS algorithm. It is a whole block diagram of this invention in the case of sharing the
speaker for cancellation with the speaker for audios.
[0008]
FIG. 1 is a block diagram of a conventional active noise control apparatus adopting the LMS
algorithm. Active noise control will be described according to this figure, and then the noise
cancellation apparatus of the present invention of FIG. 2 will be described. In FIG. 1, a reference
signal generation unit 1 generates and outputs a reference signal x that has a correlation with
10-04-2019
3
noise to be muted. For example, if noise to be muffled is engine noise, a signal correlated with
noise (engine noise) according to engine speed is generated as a reference signal. The adaptive
signal processing device 2 receives the reference signal x generated from the reference signal
generation unit 1 and receives noise NZ and cancellation noise CN at a noise cancellation
position (observation point, for example, near the driver's ear) in the vehicle compartment. A
synthetic sound signal is input as an error signal e, and adaptive signal processing is performed
so as to minimize the power of the error signal, and a noise cancellation signal y is output. The
adaptive thing processing device 2 is for signal processing by convoluting the LMS signal
processing unit ADP, the adaptive filter ADF of the digital filter configuration, and the transfer
characteristic C ^ of the cancellation sound transmission system from the speaker to the noise
cancellation point to the reference signal x. A signal processing filter SFT that generates a
reference signal is provided. The cancel speaker 3 receives the adaptive filter output signal and
emits a noise cancellation sound CN, and the microphone 4 is disposed at the noise cancellation
point, detects a synthesized sound of the noise NZ and the cancellation sound CN, and generates
a synthesized sound signal. The error signal e is input to the LMS signal processing unit ADP of
the adaptive signal processing device 2.
[0009]
The LMS signal processing unit ADP receives the error signal e at the noise cancellation point
and the signal processing reference signal u output via the signal processing filter SFT, and uses
these signals to cancel the noise at the noise cancellation point. , Adaptive signal processing to
determine the coefficient H of the adaptive filter ADF. For example, according to a known LMS
(Least Mean Square) adaptive algorithm, the LMS signal processing unit ADP uses an adaptive
filter coefficient H (n + 1) at the current time (n + 1) Update using n). The adaptive filter ADF
digitally filters the reference signal x in accordance with the coefficients determined by the LMS
signal processor ADP, and outputs a noise cancellation signal y. Note that the reference signal x
must be a signal highly correlated with the noise NZ to be eliminated, and sounds not correlated
with the reference signal are not eliminated. (1)By continuing the coefficient update of the
equation, the filter coefficients converge to a constant value to cancel the noise.
[0010]
FIG. 2 is an overall configuration diagram of the present invention when the speaker for
canceling the noise cancellation device for updating the coefficient of the adaptive filter by
equation (1) is shared with the speaker for audio, and the same parts as FIG. The code is
attached. 1) is different from FIG. 1 in that 1) the audio unit 5 is provided, 2) the audio speaker 6
10-04-2019
4
is shared as a noise canceling speaker, 3) the microphone detection signal e is transmitted to the
adaptive signal processing unit 2 when muted. The point is that a switch 7 is provided to block
input. The audio unit 5 includes an audio source (CD player, AM / FM radio, etc.) 5a, an audio
circuit 5b that performs various tone control, volume control, etc. on audio signals, a combining
unit 5c that combines audio signals and noise cancellation signals, A power amplifier 5 d for
amplifying a signal and a mute unit 5 e for muting a sound output from the speaker 6 are
provided. The DA converter is not shown. The adaptive signal processing device 2 does not
cancel the sound not correlated with the reference signal x as described in FIG. Therefore, the
adaptive signal processing device 2 cancels the audio sound even if the microphone detection
signal e includes the audio signal component by setting the reference signal x to a signal having a
high correlation with the noise (for example, the engine sound) to be canceled. Further, the
coefficient of the adaptive filter ADF is determined so as to cancel only the noise, and the noise
cancellation signal y is output.
[0011]
Therefore, when not in the mute state, the combining unit 5c combines the audio signal and the
noise cancellation signal, and the power amplifier 5d amplifies the combined signal and emits the
audio sound and the noise cancellation sound from the speaker 6 to the acoustic space. In
parallel, the adaptive signal processing unit 2 executes noise cancellation processing using the
microphone detection signal (error signal) e and the reference signal x to cancel noise (engine
sound). In this state, when the audio mute key of the mute unit 5e is turned on to mute the power
amplifier 5d, the power amplifier 5d sets the amplification degree to 0 and simultaneously stops
the output of audio sound such as music from the speaker 6, The output of the noise cancellation
sound also stops. When the mute is turned on, the switch 7 is opened to block the input of the
microphone detection signal e to the adaptive signal processing device 2 and the microphone
detection signal e to be input to the adaptive signal processing device 2 becomes zero. As a
result, even if the adaptive signal processing device 2 continues the adaptive signal processing, e
(n) = 0 in the equation (1), and the coefficient of the adaptive filter becomes H (n + 1) = H (n) It is
maintained at the muted value, and the filter coefficients do not diverge. As a result, according to
the present invention, it is possible to prevent generation of large volume noise at the time of
releasing the mute, and it is possible to perform noise cancellation immediately after releasing
the mute by using the adaptive filter coefficient at the time of muting.
[0012]
In the above, the switch is provided to block the microphone detection signal from being input to
the adaptive signal processing unit, but the DSP constituting the adaptive signal processing unit
is forced to control the microphone detection signal to be 0 at the time of muting. You can also.
10-04-2019
5
[0013]
DESCRIPTION OF SYMBOLS 1 reference signal generation part 2 adaptive control apparatus 4
error microphone 5 audio unit 5a audio source 5b audio circuit 5c combining part 5d power
amplifier 5e mute part 6 speaker ADP adaptive signal processing part ADF adaptive filter SFT
signal processing filter
10-04-2019
6
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