US 8,077,641 B2 · Echo cancellation for channels with unknown time-varying gain

Abstract

After an initial training session, a “Dynamic Echo Canceller” (DEC) provides echo cancellation where only access to an input signal and a composite output signal are available, and the input signal is subjected to an unknown variable gain function. In one embodiment, the DEC uses echo cancellation to provide a “clean” copy of a second input signal where only a first input signal and a composite of the first and second input signal is available. An example is a “black box” amplifier coupled to a microphone and a phone line, with access to only the microphone input and a combined output signal where it is desired to retrieve a clean copy of a remote caller signal from the combined output. The DEC is applicable to many fields, including: signal separation; cancellation of echoes caused by impedance mismatches, periodic electrical noise, acoustic echoes caused by acoustic coupling, etc.

Claims20

Dependent claims

A process for training a signal extractor for extracting an unknown signal from a combination signal, comprising process actions for:

receiving a first training signal;
receiving a second training signal, wherein the second training signal represents a version of the first training signal that has been subjected to an unknown time-varying gain function across a signal channel, and wherein the unknown time-varying gain function is not determined based on any other signal;
identifying coefficients of a scale-free channel model by performing a best fit of the first training signal to a normalized version of the second training signal;
and
using the coefficients of the scale-free channel model in a signal extractor for extracting an unknown signal from a combination signal and a known signal, wherein the combination signal represents a combination of the unknown signal and a version of the known signal that has been subjected to the unknown time-varying gain function across the signal channel.

2 more elements

A physical computer-readable storage media having computer executable instructions for cancelling a first signal from a combination signal, said computer executable instructions comprising:

receiving a training signal;
identifying filter coefficients corresponding to an unknown channel characteristic being applied to the training signal by performing a windowed best-fit of the training signal to a copy of the training signal that has been normalized following application of the unknown channel characteristic to the copy of the training signal, and wherein the unknown channel characteristic is not determined based on any other signal;
receiving a composite signal comprising a combination of an unknown signal and an input signal that has been that has been modified by the unknown channel characteristic;
performing a windowed projection of a version of the input signal that has been filtered by the identified filter coefficients onto the composite signal to identify a best fit of the filtered version of the input signal to the composite signal;
and
subtracting the identified best fit of the filtered version of the input signal from the composite signal to cancel the input signal from the composite signal.

3 more elements

Dependencies are inferred from the claim text.

Echo cancellation for channels with unknown time-varying gain

Life of this patent

Echo cancellation for channels with unknown time-varying gain

Life of this patent

Abstract

Claims20