Noise-level adaptive residual echo suppressor
View Patent ↗An improved echo control system has an adaptive controlled echo canceling filter arrangement in which a background filter updates the filter coefficients of an echo shaping filter responsive to a normalized least mean square (NLMS) algorithm. An adaptive control module determines a weighted reference signal for the background filter in which the weight is proportional to a far signal reference and an estimate of the norm of an echo canceller error vector, and inversely proportional to en estimate of a residue of the echo canceller. And a non-linear normalized convergence term is used in the NLMS algorithm.
1. An improved echo control system including:
an echo-containing near signal input;
an echo canceller, coupled to a far signal reference, producing an echo estimate signal output representative of the echo contained in the near signal;
a signal coupling node, coupled to the near signal input and the echo estimate signal output, producing an echo-canceled signal output having an echo residue;
an echo shaping filter, coupled to the echo-canceled signal output, reducing the echo residue and providing an echo-suppressed signal output, the echo shaping filter having a spectral response determined by filter coefficients; and
a background filter, coupled to:
(a) an error signal representative of the difference between:
(i) the echo canceled signal, and
(ii) a signal representative of background filter spectral response, and
(b) an adaptive control module producing a reference signal output that is a weighted sum of:
(i) the echo-containing signal, and
(ii) the echo canceled signal,
the background filter updating the filter coefficients of the echo shaping filter responsive to a normalized least mean square (NLMS) algorithm;
wherein the improvement comprises:
determining, in the adaptive control module, a reference signal weight for the weighted sum, the weight being proportional to the far signal reference; and an estimate of the norm of an echo canceller error vector, and inversely proportional to en estimate of a residue of the echo canceller; and
using a non-linear normalized convergence term in the NLMS algorithm.
2. An improved echo control system according to claim 1 , wherein the echo canceller is a finite impulse response (FIR) filter.
3. An improved echo control system according to claim 1 , wherein the echo shaping filter is a finite impulse response (FIR) filter.
4. An improved echo control system according to claim 1 , wherein the background filter is a finite impulse response (FIR) filter.
5. An improved echo control system according to claim 1 , wherein the echo canceller error vector is determined as:
Δ w ( k )= w ep −w ( k )
where Δw(k) represents the echo canceller error vector, w ep represents a physical echo path identified by the echo canceller, and w(k) the echo canceller response.
6. An improved echo control system according to claim 1 , wherein the reference signal weight is determined as:
α
(
k
)
=
β
Δ
w
(
k
)
x
_
s
(
k
)
e
_
s
(
k
)
where α(k) represents the reference signal weight, β represents a constant normalizing term, ∥Δw(k)∥ represents an estimate of the norm of the echo canceller error vector, {overscore (x)} s (k) represents a short-term average magnitude of the far signal reference, and ē s (k) represents a short-term average magnitude of the echo canceller residue.
7. An improved echo control system according to claim 6 , wherein the echo canceller error vector is determined as:
N
+
N
T
N
T
∑
i
=
1
N
T
w
i
(
k
)
.
8. An improved echo control system according to claim 1 , wherein the NLMS update algorithm is:
h
(
k
+
1
)
=
h
(
k
)
+
μ
ζ
+
z
(
k
)
T
z
(
k
)
z
(
k
)
e
h
(
k
)
where h(k) represents the echo shaping filter having an order L H , z(k) represents a vector representing the L H most recent values of the reference signal output, e h (k) represents the error signal, ζ represents a non-negative constant, and
μ
ζ
+
z
(
k
)
T
z
(
k
)
represents a normalized convergence coefficient.
9. An improved method of echo control including:
providing an echo-containing near signal input;
producing, with an echo canceller coupled to a far signal reference, an echo estimate signal output representative of the echo contained in the near signal;
producing, with a signal coupling node coupled to the near signal input and the echo estimate signal output, an echo-canceled signal output having an echo residue;
reducing, with an echo shaping filter coupled to the echo-canceled signal output, the echo residue and providing an echo-suppressed signal output, the echo shaping filter having a spectral response determined by filter coefficients; and
providing a background filter, coupled to:
(a) an error signal representative of the difference between:
(i) the echo canceled signal, and
(ii) a signal representative of back ground filter spectral response, and
(b) an adaptive control module producing a reference signal output that is a weighted sum of:
(i) the echo-containing signal, and
(ii) the echo canceled signal,
the background filter updating the filter coefficients of the echo shaping filter responsive to a normalized least mean square (NLMS) algorithm;
wherein the improvement comprises:
determining, in the adaptive control module, a reference signal weight for the weighted sum, the weight being proportional to the far signal reference; and an estimate of the norm of an echo canceller error vector, and inversely proportional to en estimate of a residue of the echo canceller; and
using a non-linear normalized convergence term in the NLMS algorithm.
10. An improved echo control method according to claim 9 , wherein the echo canceller is a finite impulse response (FIR) filter.
11. An improved echo control method according to claim 9 , wherein the echo shaping filter is a finite impulse response (FIR) filter.
12. An improved echo control method according to claim 9 , wherein the background filter is a finite impulse response (FIR) filter.
13. An improved echo control method according to claim 9 , wherein the echo canceller error vector is determined as:
Δ w ( k )= w ep −w ( k )
where Δw(k) represents the echo canceller error vector, w ep represents a physical echo path identified by the echo canceller, and w(k) the echo canceller response.
14. An improved echo control method according to claim 9 , wherein the reference signal weight is determined as:
α
(
k
)
=
β
Δ
w
(
k
)
x
_
s
(
k
)
e
_
s
(
k
)
where α(k) represents the reference signal weight, β represents a constant normalizing term, ∥Δw(k)∥ represents an estimate of the norm of the echo canceller error vector, {overscore (x)} s (k) represents a short-term average magnitude of the far signal reference, and ē s (k) represents a short-term average magnitude of the echo canceller residue.
15. An improved echo control method according to claim 14 , wherein the echo canceller error vector is determined as:
N
+
N
T
N
T
∑
i
=
1
N
T
w
i
(
k
)
.
.
16. An improved echo control method according to claim 9 , wherein the NLMS update algorithm is:
h
(
k
+
1
)
=
h
(
k
)
+
μ
ζ
+
z
(
k
)
T
z
(
k
)
z
(
k
)
e
h
(
k
)
where h(k) represents the echo shaping filter having an order L H , z(k) represents a vector representing the L H most recent values of the reference signal output, e h (k) represents the error signal, ζ represents a non-negative constant, and
μ
ζ
+
z
(
k
)
T
z
(
k
)
represents a normalized convergence coefficient.