conceptual key to this invention is that the signals received
at two closely spaced microphones in a multipath acoustic environment
are each made up of a sum of echoes of the signal received at
the other one. This leads to the conclusion that the difference
between the two microphone signals is a sum of echoes of the
acoustic source in the environment. In the absence of a speech
source, the ANS scheme proposed by Jaber first attempts to isolate
the difference signal at each of the microphones by subtracting
from it an adaptively predicted version of the other microphone
signal. It then attempts to adaptively cancel the two difference
signals. When speech is present (as detected by some type of
vocoder-based strategy), the adaptive cancellation stage has
its adaptivity turned off (i.e. the impulse responses of the
two FIR filters, one for each microphone, are unchanged for
the duration of the speech). The effect here is that the adaptive
canceller does not end up cancelling the speech signal contained
in the difference between the two microphone signals.
SUPPRESSION SYSTEM WITH DUAL MICROPHONE ECHO CANCELLATION",
US patent No. US 6,738,482 B1.
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