Symmetry based subband acoustic echo cancellation

Details Symmetry based subband acoustic echo cancellation Symmetry based subband acoustic echo cancellation

2000-05-18

2004-06-29

Isen, Forester W. (Department: 2644)

Telephonic communications

Echo cancellation or suppression

Using digital signal processing

C379S406010, C379S406020, C379S406060, C379S406080, C379S406090, C379S406120, C379S406130

Reexamination Certificate

active

06757385

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to bidirectional audio communications and, more particularly, to echo cancellation in such communications.
BACKGROUND OF THE INVENTION
FIG. 1
illustrates a conventional communication device in which echo cancellation techniques are utilized. The device of
FIG. 1
could be, for example, a telephone (fixed or mobile) including a hands-free speaker/microphone arrangement at
14
. A signal x
far
from a far-end source is reproduced at loudspeaker
11
. When the sound emerges from loudspeaker
11
, it bounces off of surrounding structures and back into a microphone
13
that also receives a signal x
near
from a near-end source. Because of this echo phenomenon, a listener at the far end can actually perceive an echo of the sound produced at the far end.
To eliminate such echos, a filter with adjustable filter taps is conventionally applied as illustrated at
17
and
19
in FIG.
1
. The values of the filter taps are controlled by an adaptive algorithm (e.g., a Least Mean Squares algorithm) illustrated at
17
such that the echo canceller filter at
19
resembles as closely as possible the echo path between the loudspeaker
11
and the microphone
13
. The estimated echo produced by the echo canceller filter
19
is subtracted at
15
from the signal output from the microphone
13
, such that, ideally, only the near-end signal x
near
remains as the resulting signal
12
.
Conventional techniques of eliminating acoustical echos in communication devices such as illustrated in
FIG. 1
have heretofore employed algorithms that operate on the entire frequency range supported by the communication device, for example 300-3400 Hz for a typical conventional telephone.
According to the present invention, improved echo cancellation performance is achieved by dividing the audio signal into subbands, and applying echo cancellation techniques in the subbands. Advantageously, by applying echo cancellation techniques in subbands, the adaptive filter used for echo cancellation can be simplified.


REFERENCES:
patent: 4677668 (1987-06-01), Ardalan et al.
patent: 5396554 (1995-03-01), Hirano et al.
patent: 5436940 (1995-07-01), Nguyen
patent: 5553014 (1996-09-01), De Leon, II et al.
patent: 5566167 (1996-10-01), Duttweiler
patent: 5568558 (1996-10-01), Ramm et al.
patent: 5761318 (1998-06-01), Shimauchi et al.
patent: 5889857 (1999-03-01), Boudy et al.
patent: 0 739 102 (1996-10-01), None
patent: 0739102 (1996-10-01), None
International Search Report for PCT/EP 00/04860 Completed Nov. 17, 2000.

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