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JPH0447705

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DESCRIPTION JPH0447705
[0001]
FIELD OF THE INVENTION The present invention relates to a noise tolerant adaptive equalizer
under noisy environment. 2. Description of the Related Art In recent years, methods have been
proposed for correcting acoustic characteristics including speakers by using digital signal
processing techniques such as adaptive filters. Heretofore, this type of adaptive equalizer has
generally been configured as shown in Japanese Patent Laid-Open No. 1240099. The
configuration will be described below with reference to FIG. As shown in FIG. 4, the acoustic
signal input to the acoustic signal input terminal 1 is corrected by the adaptive filter 33 and
emitted from the speaker 10, and the signal received by the microphone 9 is delayed in advance
to the input signal. The adaptive filter 33 is always controlled via the coefficient controller 6 so
that the signal set by the characteristic setting unit 32 is compared by the adder 34 and the
signal becomes smaller. SUMMARY OF THE INVENTION However, in the above-described
conventional configuration, when external noise enters the microphone 9 during the operation of
the adaptive filter 33, a malfunction occurs in the adaptation processing, which requires a long
time for convergence, or convergence There was a problem that it could be impossible. The
present invention solves the above-mentioned conventional problems, and an object of the
present invention is to provide a noise resistant adaptive equalizer capable of performing
adaptive processing accurately even in a noisy environment. Means for Solving the Problems In
order to solve the above problems, the noise resistant adaptive equalizer according to the present
invention comprises a noise detector installed near a noise source, and a first adaptive filter for
receiving an output of the noise detector. A second adaptive filter connected to an audio signal
input terminal, an equalizer of a desired characteristic connected to the audio signal input
terminal, a speaker cascade-connected to the second adaptive filter, and sound reception from
the speaker A microphone placed at a point, a first subtractor for subtracting the output of the
equalizer from the output of the microphone, and a second subtractor for subtracting the output
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of the first adaptive filter from the output of the first subtractor A filter coefficient controller
using the output of the second subtractor as an error input, and an acoustic input signal input to
the acoustic signal input terminal or a signal from the noise detector First selecting means for
selecting one of the filter coefficients and inputting it to the reference input of the filter
coefficient controller, and the coefficient output of the filter coefficient controller for the
coefficient memory of the first adaptive filter or the second adaptive filter And second selecting
means for selecting and inputting one of the coefficient memories, wherein first, the first
selecting means is selected as the signal of the noise detector, and the second selecting means is
selected as the first selecting means. Selecting the coefficient memory of the first adaptive filter
to operate the filter coefficient controller, then selecting the first selection means for the acoustic
input signal, and the second selection means for the second The filter coefficient controller is
operated by selecting it as the coefficient memory of the adaptive filter.
Operation With the above configuration, the noise detector detects the noise signal that has
entered the microphone at the listening position and cancels the noise signal with the signal
obtained by applying the adaptive filter processing to the noise signal, and then operates the
adaptive equalizer for acoustic characteristic correction. Therefore, accurate adaptive operation
is possible regardless of noise. Examples of the present invention will be described below with
reference to the drawings. FIG. 1 is a block diagram of a noise resistant adaptive equalizer
according to an embodiment of the present invention. The present embodiment is aimed to
accurately perform the adaptive processing of the acoustic correction equalizer even under a
noise environment. As shown in FIG. 1, 2 is a noise detector installed near the noise source 12, 7
is an adaptive filter for receiving the output of the noise source 12, 11 is an adaptive filter
connected to the acoustic signal input terminal 1, 3 is an Equalizer 10 connected to acoustic
signal input terminal 1 and having desired characteristics set, speaker 10 connected in cascade
to adaptive filter 11, microphone 9 installed at the point of receiving sound from speaker 10,
equalizer 13 from output of microphone 9 3, a subtractor for subtracting the output of 3, a
subtractor for subtracting the output of the adaptive filter 7 from the output of the subtracter 13,
a filter coefficient controller using the output of the subtractor 8 as an error input, and 4 for an
acoustic signal input First selection means for switching between the acoustic input signal
inputted to the terminal 1 and the signal output of the noise detector 2 and connecting it to the
coefficient controller 6, 5 is suitable for the output of the coefficient controller 6 with the
adaptive filter 7. A second selection means for switching the filter 11. Hereinafter, the operation
of the above configuration will be described. At first, processing of removing the influence of the
noise source 12 is performed without inputting an acoustic signal. That is, the selection means 4
and 5 are selected to the A side. An equivalent block diagram at this time is shown in FIG. In FIG.
2, the detection signal of the noise detector 2 is input to the adaptive filter 7, and the noise signal
received by the microphone 9 installed at the listening position is subtracted by the subtracter 8
and the coefficient controller 6 outputs an error signal. Is entered as The coefficient controller 6
calculates the filter coefficient using an algorithm such as learning identification method
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( application of digital signal processing jp 219 corona company telecommunications society )
so that this error signal becomes small, and writes it in the coefficient memory of the adaptive
filter 7 . That is, the adaptive filter 7 is identified to the acoustic transmission characteristic from
the noise source 12 to the microphone 9, and the output of the subtractor 8 can remove the
influence of the signal of the noise source. Next, the selection means 4 and 5 are selected to the B
side, and an acoustic signal is input to the input terminal 1.
An equivalent block diagram at this time is shown in FIG. In FIG. 3, an input signal is emitted
from a speaker 10 through an adaptive filter 11, passes through an acoustic transmission
system, and is received by a microphone 9 at a listening position. On the other hand, after the
acoustic signal input to the acoustic signal input terminal 1 is subtracted from the sound
reception signal of the microphone 9 by the subtractor 13 through the equalizer 3 given the
desired characteristics, and after the noise signal is removed by the subtractor 8, The error signal
is input to the coefficient controller 6. The coefficient controller 6 similarly calculates a
coefficient which makes this error signal smaller, and writes it to the coefficient memory of the
adaptive filter 11. Thus, by performing the adaptive processing, the coefficients of the adaptive
filter 11 converge so that the acoustic transmission system including the speaker approximates
the desired characteristics set in the equalizer. Thus, according to the embodiment of the present
invention, the influence can be eliminated even under noise. Also, by using the coefficient
controller operation and algorithm in common when identifying the noise transmission system
and when adapting the equalizer, it is possible to switch and use a coefficient controller with a
large amount of computation, so that the overall Hardware is reduced. As described above,
according to the present invention, the signal detected by the noise detector is subjected to
adaptive filtering to cancel the noise signal, and then the adaptive equalizer for acoustic
characteristic correction is operated. The adaptation processing of the acoustic correction
equalizer can be accurately performed under the following conditions.
[0002]
Brief description of the drawings
[0003]
1 is a block diagram of a noise resistant adaptive equalizer according to an embodiment of the
present invention, FIG. 2 is an equivalent block diagram when the selection means of the noise
resistant adaptive equalizer is A side, and FIG. 3 is the noise resistant adaptive FIG. 4 is a block
diagram of a conventional noise tolerant adaptive equalizer when the equalizer selection means
is on the B side.
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Reference Signs List 1: acoustic signal input terminal 2: noise detector 3: equalizer 4, 5: selection
means 6: coefficient controller 7, II: adaptive filter 8 . ■ 3 ... Subtractor, 9 ... Microphone, IO ...
Speaker. Agent Yoshimoto Mori Motohiro
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