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DESCRIPTION JP2003318784

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DESCRIPTION JP2003318784
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic echo canceller system applied to a hands free device and a video conference system.
[0002]
2. Description of the Related Art Conventionally, as a technique for reducing an echo amount in
an acoustic echo canceller system, as disclosed in Japanese Patent No. 02861888, Japanese
Patent Laid-Open No. 2000-59270, and Japanese Patent Laid-Open No. 2000-040985. It is
common to adjust the gain of the input and output. FIG. 5 is a block diagram of a conventional
echo canceller system. This echo canceller system performs processing of a microphone 1, a
volume control unit 2, a subtractor 3 for subtracting the calculated estimated echo and the actual
echo, a volume control unit 4 for adjusting the gain to be sent to the line, and reduction of
residual echo. The noise control unit 5, an adaptive filter 6 having a function of estimating the
transfer function between the microphone 1 and the speaker and updating the filter coefficient
automatically, the speaker 7 for transmitting the voice from the line, and the volume of the
speaker 7 are adjusted. The volume control unit 8 includes a volume control unit 10 that adjusts
the gain of the sound from the line. When optimal gain adjustment is performed in each of the
volume control blocks 2, 4, 8 and 10 in the figure, the amount of echo transmitted to the line is
minimized. Another way to reduce the amount of echo is to use a directional microphone.
[0003]
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However, although the amount of echo decreases when gain adjustment is performed, there is a
problem that the sound is small and it is difficult for the user to hear in actual use. In particular,
if the gain is reduced by the volume control unit 10 shown in FIG. 5, it will be difficult for the
user A to listen, and when the volume control unit 4 decreases the gain, the user B will be
difficult to hear. As described above, since the adjustment of the echo amount and the user's ease
of hearing are contradictory, there is a limit to gain adjustment alone. Therefore, it is considered
to adjust not only the gain but also the unnecessary sound that can not be heard in the auditory
sense (sound to be an auditory mask) to be adjusted. Due to the influence of the transfer
characteristic of the user A side, the sound generated from the speaker of the user A side may be
input to the microphone as a sound that should not normally be heard (it will be an auditory
mask). An object of the present invention is to provide an echo canceller system capable of
removing such echo components and further reducing residual echo without causing discomfort
to the user.
[0004]
SUMMARY OF THE INVENTION In order to achieve the above object, the invention according to
claim 1 generates an estimated echo signal with reference to a voice signal from a line, and a
microphone and an actual residual echo signal. An echo canceller system comprising: an adaptive
filter having a function of estimating a transfer function between speakers and updating a filter
coefficient; and a subtractor for subtracting an estimated echo signal from a real echo signal
input from a microphone, which is an auditory characteristic An echo canceller system having
auditory masking means for removing components presumed to be masked in the voice signal
from the line is the most important feature. The invention according to claim 2 is characterized in
that, in the echo canceller system according to claim 1, an echo canceller system in which
successive masking is introduced into auditory mask processing by auditory mask processing
means is a main feature.
[0005]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described in detail below with reference to the drawings. FIG. 1 is a block diagram of an echo
canceller system according to an embodiment of the present invention. This echo canceller
system performs processing of a microphone 1, a volume control unit 2, a subtractor 3 for
subtracting the calculated estimated echo and the actual echo, a volume control unit 4 for
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adjusting the gain to be sent to the line, and reduction of residual echo. The noise control unit 5,
an adaptive filter 6 having a function of estimating the transfer function between the microphone
1 and the speaker and updating the filter coefficient automatically, the speaker 7 for transmitting
the voice from the line, and the volume of the speaker 7 are adjusted. A sound volume control
unit 8, an auditory mask processing unit 9 for removing unnecessary sounds that can not be
heard aurally (sounds to be aural mask), and a sound volume control unit 10 for adjusting the
gain of the sound from the line. First, a first example of echo cancellation processing will be
described. The voice of the user B transmitted from the line is first adjusted in gain by the
volume control unit 10. Thereafter, the auditory mask processing unit 9 removes components
that are determined not to be heard by the user A. Here, simultaneous masking is used as a
model to be removed. The simultaneous masking is a model in which the acoustic component to
be masked and the acoustic component to be masked exist on the same area as shown in FIG.
The signal processed by the auditory mask processing unit 9 becomes a reference signal of the
adaptive filter 6 and is transmitted to the user A side, and after being adjusted in volume by the
volume control unit 8, transmitted to the user A by the speaker 7. The sound generated from the
speaker 7 is input from the microphone 1 as an actual echo. Here, this signal has a component
that the auditory mask processing unit 9 determines that the user A can not hear, so that the
component can be sensed by the user B under the influence of the transfer characteristic on the
user A side. It is not input as a real echo. The signal from the microphone 1 is then adjusted in
gain by the volume control unit 2 and subtracted from the output of the adaptive filter 6 by the
subtractor 3. The subtracted signal becomes a residual echo, and after being gain-adjusted by the
volume control unit 4, passes through the noise control unit 5 for removing noise and is
transmitted to the line. Next, a second example of echo cancellation processing will be described.
The voice of the user B transmitted from the line is first adjusted in gain by the volume control
unit 10. Thereafter, the auditory mask processing unit 9 removes components that are
determined not to be heard by the user A. Here, successive masking is used as a model to be
removed. The temporal masking is a model in which the acoustic component to be masked and
the acoustic component to be masked are temporally different as shown in FIG.
The case shown in FIG. 3 is the case where the masking sound is in front of the masked sound,
which is called forward masking. Also, as shown in FIG. 4, the sound to be masked may be after
the sound to be masked. This is called retrogressive masking (backward masking). The auditory
mask processing unit 9 removes these components. The signal processed by the auditory mask
processing unit 9 becomes a reference signal of the adaptive filter 6 and is transmitted to the
user A side, and after being adjusted in volume by the volume control unit 8, transmitted to the
user A by the speaker 7. The sound generated from the speaker 7 is input from the microphone 1
as an actual echo. Here, this signal has a component that the auditory mask processing unit 9
determines that the user A can not hear, so that the component can be sensed by the user B
under the influence of the transfer characteristic on the user A side. It is not input as a real echo.
The signal from the microphone 1 is then adjusted in gain by the volume control unit 2 and
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subtracted from the output of the adaptive filter 6 by the subtractor 3. The subtracted signal
becomes a residual echo, and after being gain-adjusted by the volume control unit 4, passes
through the noise control unit 5 for removing noise and is transmitted to the line.
[0006]
As is apparent from the above description, according to the present invention, the following
effects can be obtained.
[0007]
In the echo canceller system according to the first aspect of the present invention, although the
gain adjustment is limited, it is possible to reduce the amount of echo without giving a burden to
the user by utilizing the auditory characteristic. Can reduce the residual echo.
In the echo canceller system according to the second aspect of the present invention, it is
possible to further reduce the amount of echo without giving a burden to the user by utilizing the
successive masking, and in turn, it is possible to reduce the residual echo.
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