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DESCRIPTION JP2002135170

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DESCRIPTION JP2002135170
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
echo cancellation apparatus, echo cancellation method, and recording medium recording echo
cancellation program for erasing echoes which cause feedback and acoustic feedback mainly in
loud speech systems. .
[0002]
2. Description of the Related Art With the spread of voice conferences, there is a demand for the
provision of a speech communication system which is excellent in simultaneous call performance
and has little echo. An echo canceler is one that meets this requirement. FIG. 1 shows a block
diagram of a conventional echo canceler. A / D converter 8 receives an incoming call in a speech
communication system including a reception system from reception signal end 1 receiving
reception signal x (t) to speaker 2 and a transmission system from microphone 3 to transmission
output end 4 The signal x (t) is sampled, and the received signal x (t) is supplied to the pseudo
echo path (FIR filter) 7, and the pseudo echo signal y ^ (k) from the pseudo echo path 7 is
converted to A / D. The echo signal y (k) is eliminated by subtracting the echo signal y (k)
sampled by the converter 5 from the echo signal y (k) by the subtracter 9 to obtain a residual
signal e (k).
[0003]
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Here, the pseudo echo path 7 needs to follow the time-dependent fluctuation of the echo path,
and is estimated sequentially by the estimation circuit 6 so that the residual signal e (k) = y (k)
−y ^ (k) approaches 0. By correcting the pseudo echo path 7, appropriate echo cancellation is
always performed. For example, a learning identification method is used for successive correction
of the impulse response h ^ (k) of the pseudo echo path 7, and the estimation algorithm is
updated using the update equation (2) so as to satisfy the equation (1). Ru. y (k) = xT (k) h ^ (k +
1) (1) h ^ (k + 1) = h ^ (k) + β (k) x (k) (2) where β (k ) Is determined as follows.
[0004]
y (k) = xT (k) {h ^ (k) + β (k) x (k)} y (k) = xT (k) h ^ (k) + xT (k) β (k) x (k) y (k) -xT (k) h ^ (k) =
β (k) xT (k) x (k) where e (k) = y (k) -xT (k) h ^ (k) and Then, e (k) = β (k) × T (k) × (k) β (k) = e
(k) / xT (k) × (k) is substituted into equation (2), and finally the step size Using α, h ^ (k + 1) = h
^ (k) + αe (k) x (k) / xT (k) x (k) h ^ (k) = [h1 ^ (k), h2 ^ (k),..., hN ^ (k)] Tx ^ (k) = [x (k), x (k-1), ...,
x (k-L + 1)] Te (k) = Y (k)-x T (k) h ^ (k) (α: step size (scalar amount, constant), L: number of taps,
T: vector transpose), impulse response h ^ of pseudo echo path 7 Let k) approach the impulse
response h (k) of the true echo path.
[0005]
Here, the impulse response of the echo path to be estimated is exponentially attenuated as shown
in the reverberation curve of FIG. 2, and an exponential weighting algorithm is proposed to
reflect it on the step size and to accelerate the convergence speed (for example, , JP-A-1220530).
This method uses a step size matrix A instead of the scalar step size. A is a diagonal matrix, and
its elements are [α1, α2, ..., αL]. Here, αi is represented by αi = α1γi-1 (3) (γ: exponential
attenuation coefficient). This improves the convergence speed as shown in FIG. In FIG. 3, “ES
(Exponential Weighted Step Size) method” indicates an exponential weighting algorithm, and
“NLMS (Normalize Least Mean Square)” indicates a learning identification method.
[0006]
The estimation algorithm using the step size matrix A is updated using the update equation (5) so
as to satisfy the equation (4). y (k) = xT (k) h ^ (k + 1) (4) h ^ (k + 1) = h ^ (k) + β (k) Ax (k) (5)
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where, β (k) Is determined as follows. y (k) = xT (k) {h ^ (k) + β (k) Ax (k)} y (k) = xT (k) h ^ (k) +
xT (k) β (k) Ax (k) y (k) -xT (k) h ^ (k) = β (k) xT (k) Ax (k) e (k) = β (k) xT (k) Ax (k) β (k) = e
Substituting in (k) / xT (k) Ax (k) equation (5), introducing a step size matrix, the impulse
response of the pseudo echo path can be obtained by the following equation. h ^ (k + 1) = h ^ (k)
+ αe (k) Ax (k) / xT (k) Ax (k)
[0007]
The step size matrix simulating the impulse response of the echo path of the conventional echo
canceler is usually set in a standard room. However, the impulse response of the echo path
differs from room to room. FIG. 4 shows reverberation curves of impulse responses of two
different rooms (room A and room B). These impulse response exponential attenuation amounts
are different, and there is a problem that the conventional echo canceler can not estimate the
impulse response with sufficient accuracy and at high speed and can not cancel the echo with
sufficient performance.
[0008]
The present invention has been made in view of the above problems, and it is an object of the
present invention to set the step size matrix to an optimum value and further accelerate the
convergence speed by using the impulse response coefficient of the echo path after convergence.
Do.
[0009]
SUMMARY OF THE INVENTION The present invention focuses on the fact that the impulse
response of the pseudo echo path is equal to or very similar to the impulse response of the echo
path when the echo signal can be eliminated by the pseudo echo signal. And estimating the
exponential decay coefficient γ of the step size matrix that is optimal for the impulse response
of the echo path from the coefficients of the impulse response of the pseudo echo path at that
time.
According to the present invention, as described above, since the exponential attenuation
coefficient of the step size matrix can be set to the impulse response of the echo path, an echo
canceler with good convergence characteristics can be obtained.
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[0010]
The invention according to claim 1 generates a pseudo echo path by sequentially estimating the
impulse response of the echo path by the estimation algorithm from the transmission signal to
the echo path and the echo signal after passing through the echo path of the transmission signal.
And an echo canceler for eliminating the echo signal by subtracting the pseudo echo signal
obtained by using the transmission signal as the input of the pseudo echo path from the echo
signal, the step size in the estimation algorithm being the pseudo echo A step size matrix storage
circuit for storing a step size matrix weighted by the exponential decay characteristic of the
impulse response of the sound field for setting each coefficient of the impulse response of the
path, the pseudo acoustic signal from the echo signal And a convergence determination circuit
that determines whether or not the echo signal can be satisfactorily eliminated based on the
residual signal from which the And having a damping coefficient calculation circuit to reflect the
better the decision that can be erased by calculating the damping coefficient from the coefficient
of the estimated echo path Motoma' from the estimation algorithm the step size matrix No..
[0011]
The invention according to claim 2 is characterized in that, in the echo canceler according to
claim 1, the estimation algorithm is any one of a learning identification method, an LMS method,
an affine projection method, or an RLS method.
The invention according to claim 3 generates a pseudo echo path by sequentially estimating the
impulse response of the echo path by the estimation algorithm from the transmission signal to
the echo path and the echo signal after passing through the echo path of the transmission signal.
And an echo cancellation method for canceling the echo signal by subtracting the pseudo echo
signal obtained by using the transmission signal as the input of the pseudo echo path from the
echo signal, the step size in the estimation algorithm being the pseudo echo A step size matrix
weighted by the exponential decay characteristics of the impulse response of the sound field to
be set for each coefficient of the impulse response of the path is stored, and based on the
residual signal obtained by subtracting the pseudo acoustic signal from the echo signal. The
estimation algorithm is determined by determining whether the echo signal can be erased well
and the echo signal can be erased well. Wherein the calculating the attenuation coefficients from
the coefficient of al Motoma' pseudo echo path is reflected in the step size matrix.
[0012]
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The invention according to claim 4 is characterized in that, in the echo cancellation method
according to claim 3, the estimation algorithm is any one of a learning identification method, an
LMS method, an affine projection method, or an RLS method. The invention according to claim 5
generates a pseudo echo path by sequentially estimating the impulse response of the echo path
by the estimation algorithm from the transmission signal to the echo path and the echo signal
after passing through the echo path of the transmission signal. Recording an echo cancellation
program for causing a computer to execute the process of erasing the echo signal by subtracting
the pseudo echo signal obtained by setting the transmission signal as the input of the pseudo
echo path from the echo signal Storing in the medium, a step size matrix weighted by an
exponential decay characteristic of an impulse response of a sound field for setting a step size in
the estimation algorithm for each coefficient of an impulse response of the pseudo echo path;
Whether the echo signal has been successfully eliminated based on the residual signal obtained
by subtracting the pseudo acoustic signal from the echo signal And a process of calculating an
attenuation coefficient from the coefficient of the pseudo echo path obtained from the estimation
algorithm based on the judgment that the echo signal can be erased well and reflecting it on the
step size matrix. .
[0013]
The invention according to claim 6 is characterized in that, in the recording medium recording
the echo cancellation program according to claim 5, the estimation algorithm is any one of a
learning identification method, LMS method, affine projection method, or RLS method. .
[0014]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 5 shows an embodiment of
the present invention, and shows the configuration of a portion corresponding to the estimation
circuit 6 in FIG.
11The convergence judgment circuit shown by, observes the residual signal e (k) and becomes
sufficiently small (becomes smaller than the set threshold) or the received signal x (k) and the
residual signal e (k) It is observed that the received signal x (k) is sufficiently large and the
residual signal e (k) is sufficiently small, that is, it is determined whether the echo signal can be
satisfactorily eliminated (the adaptive filter has converged or not). I do. As an example of the
judgment that the adaptive filter has converged, the ratio of the power of the residual signal e (k)
to the power of the received signal x (k) is smaller than a certain threshold, that is, the echo is
good by the adaptive filter When it is considered to be erased, the information (signal) that echo
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cancellation is possible is transmitted to the attenuation coefficient calculation circuit shown at
12. The attenuation coefficient calculation circuit receives information on the coefficient ^ of the
pseudo echo path estimated from the estimation circuit based on the signal that echo
cancellation can be performed, and reflects it to calculate the step size matrix A, and the
calculated step size Pass the matrix to the estimation circuit. The estimation circuit can estimate
the impulse response at high speed by estimating the impulse response using the calculated step
size matrix.
[0015]
In the damping coefficient calculation circuit 12 of FIG. 5, the step size matrix A obtains the
reverberation time using the estimated impulse response (adaptive filter coefficient) of the echo
path, and the elements of each step size matrix are obtained from the equation (3) above. Ask for
The exponential attenuation coefficient γ for determining each element of the step size matrix is
determined, for example, as follows. Here, an example is shown in which the reverberation time
is determined from three observation points. Assuming that the adaptive filter length is L,
attenuation amounts at three observation points (L / 4, L / 2, 3L / 4) are obtained as follows.
[0017]
The inclination is obtained from the obtained R1, R2 and R3, and the average inclination Δg of
the reverberation curve per one tap is calculated. Δg = 2 {(R3−R2) + (R2−R1)} / L
reverberation time (time until sound energy attenuates from the first steady state by 60 dB) Rt
can be calculated by the following equation. Rt = {(− 60−R2) / Δg + L / 2} / fs where fs is a
sampling frequency. The exponential decay coefficient γ of the equation (3) is given by the
following equation from the obtained Rt.
[0018]
γ = exp (−μ) where μ (index representing the attenuation characteristic) is determined by the
following. 10log 10 exp (-μ Rt) 2 = -60 log 10 exp (-μ Rt) = -3 exp (-μ Rt) = 10 -3-μ Rt = log e
10 -3 μ = log e 10 -3 / R t Therefore, γ in equation (3) is It can be asked. γ = exp (-3 loge 10 /
Rt)
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[0019]
FIG. 6 shows the simulation result according to the present invention, and it can be seen that,
after the adaptive filter has converged, the impulse response of the echo path changes most
rapidly when it changes. Referring to FIG. 6, in the initial stage of learning (before echo path
change), the same convergence speed as that of the conventional ES method is shown, but the
threshold considered to be able to sufficiently reduce the echo (for example, the echo reduction
amount is 25 dB Above, etc.) The amount of attenuation is determined from the impulse response
estimated in the following cases, and is reflected in the step size. Since the step size is used for
impulse response estimation after the echo path changes, the convergence speed is faster than
the conventional ES method.
[0020]
As the estimation algorithm used in the present invention, in addition to the learning
identification method, LMS (Least Mean Square) method, affine projection method, RLS
(Recursive Least Square) method can also be used. The echo canceler according to the present
invention comprises a computer having a CPU, a memory, etc., a user terminal as an access
subject, and a recording medium, and the recording medium is a machine-readable record such
as a CD-ROM, a magnetic disk, or a semiconductor memory. A medium, the echo canceler
program recorded therein is read by the computer to control the operation of the computer to
realize the above-described components on the computer.
[0021]
According to the present invention, by adaptively updating the exponent weighting algorithm of
the echo canceler, the convergence speed can be increased when the impulse response of the
echo path changes. In this case, it is not necessary to estimate the reverberation time by the
initial training.
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