US 5,305,307 A · Adaptive acoustic echo canceller having means for reducing or eliminating echo in a plurality of signal bandwidths

Abstract

An echo cancelling device for reducing acoustic feedback between a loudspeaker and microphone in a full duplex communication system such as a telephone conferencing system. The device includes a whitening filter which flattens the microphone signal's spectrum and reduces its auto-correlation. A first signal splitter separates the whitened microphone signal into a plurality of bandlimited microphone signals. The loudspeaker signal is similarly whitened and separated into a plurality of bandlimited loudspeaker signals. A plurality of adaptive echo estimators estimate the echo in each frequency band defined by the above signal splitters. More specifically, each estimator generates an echo estimation signal representing an approximation of the acoustic feedback of a corresponding bandlimited loudspeaker signal into the microphone. To cancel echo, a subtractor removes each echo estimation signal from the bandlimited microphone signal of the same frequency band as the estimation signal. The device further processes the echo corrected signal in each band with a center clipper, to remove any residual echo, and with a noise filler to simulate the background signals removed by the clippers.

Claims40

Dependent claims

An echo cancelling device for reducing the effects of acoustic feedback between a loudspeaker and microphone in a communication system, comprising:

a first signal splitter for separating a microphone signal into a plurality of bandlimited microphone signals,
a second signal splitter for separating a loudspeaker signal into a plurality of bandlimited loudspeaker signals, the band of frequencies of each bandlimited loudspeaker signal being approximately the same as the band of frequencies of a corresponding bandlimited microphone signal,
a plurality of band echo estimators, each band echo estimator for generating an echo estimation signal for a bandlimited loudspeaker signal, said echo estimation signal representing an approximation of the acoustic feedback of said bandlimited loudspeaker signal into a corresponding bandlimited microphone signal,
at least one subtractor for subtracting an echo estimation signal from a bandlimited microphone signal of the same frequency band as the echo estimation signal to produce a bandlimited echo corrected microphone signal,
means for estimating whether a first bandlimited echo corrected microphone signal is substantially derived from acoustic feedback between said loudspeaker and said microphone, and
at least one signal clipper for attenuating said first bandlimited echo corrected microphone signal during periods of time during which said first bandlimited echo corrected microphone signal is substantially derived from acoustic feedback between said loudspeaker and microphone.

3 more elements

An echo cancelling device for reducing the effects of acoustic feedback between loudspeaker and microphone in a communication system, comprising:

a first signal splitter for separating a near end microphone signal into a plurality of bandlimited microphone signals,
a second signal splitter for separating a loudspeaker signal into a plurality of bandlimited loudspeaker signals, the band of frequencies of each bandlimited loudspeaker signal being approximately the same as the band of frequencies of a corresponding bandlimited microphone signal,
a plurality of adaptive echo estimators, each adaptive echo estimator for generating an echo estimation signal for an associated bandlimited loudspeaker signal, said echo estimation signal representing an approximation of the acoustic feedback of said bandlimited loudspeaker signal into a corresponding bandlimited microphone signal,
at least one subtractor for subtracting an echo estimation signal from an associated bandlimited microphone signal having the same frequency band as said echo estimation signal, to produce a bandlimited echo corrected microphone signal,
at least one local speech detector for identifying periods of time during which said near end microphone signal is substantially derived from acoustic feedback between said loudspeaker and microphone, and
at least one adjustment module for adjusting characteristics of at least one said adaptive echo estimator during said identified periods of time.

3 more elements

An echo cancelling device for reducing the effects of acoustic feedback between a loudspeaker and microphone in a communication system, comprising:

a first whitening filter for receiving a near end microphone signal and generating in response thereto a whitened version of said near end microphone signal,
a first signal splitter for separating said whitened microphone signal into a plurality of bandlimited microphone signals,
a second whitening filter for receiving a loudspeaker signal and generating in response thereto a whitened version of said loudspeaker signal,
a second signal splitter for separating said whitened loudspeaker signal into a plurality of bandlimited loudspeaker signals, the band of frequencies of each bandlimited loudspeaker signal being approximately the same as the band of frequencies of a corresponding bandlimited microphone signal,
a plurality of adaptive echo estimators, each adaptive echo estimator for generating an echo estimation signal for an associated bandlimited loudspeaker signal, said echo estimation signal representing an approximation of the acoustic feedback of said bandlimited loudspeaker signal into a corresponding bandlimited microphone signal,
a subtractor means for subtracting from each bandlimited microphone signal an echo estimation signal having the same frequency band as the bandlimited microphone signal, to produce a bandlimited echo corrected microphone signal,
a plurality of local speech detectors each for identifying periods of time during which a corresponding bandlimited microphone signal is substantially derived from acoustic feedback between said loudspeaker and microphone, and
a plurality of adjustment modules each for adjusting characteristics of at least one said adaptive echo estimator during said identified periods of time when a corresponding bandlimited microphone signal is substantially derived from acoustic feedback, and
a plurality of signal clippers, each clipper for attenuating a corresponding bandlimited echo corrected microphone signal during periods of time during which said bandlimited echo corrected microphone signal is substantially derived from acoustic feedback between said loudspeaker and microphone, and
a plurality of noise fillers, each noise filler comprising:
a means for generating a background noise estimation signal representing the background noise contained in a bandlimited microphone signal, and
a means for adding said background estimation signal to said attenuated bandlimited echo corrected microphone signal in an amount complementary to the magnitude of said attenuation.

9 more elements

A method for reducing the effects of acoustic feedback between a loudspeaker and microphone in a communication system, comprising the steps of:

separating a microphone signal into a plurality of bandlimited microphone signals,
separating a loudspeaker signal into a plurality of bandlimited loudspeaker signals, the band of frequencies of each bandlimited loudspeaker signal being approximately the same as the band of frequencies of corresponding bandlimited microphone signal,
generating an echo estimation signal for each bandlimited loudspeaker signal, each said echo estimation signal representing an approximation of the acoustic feedback of a bandlimited loudspeaker signal into a corresponding bandlimited microphone signal,
subtracting an echo estimation signal from a bandlimited microphone signal of the same frequency band as the echo estimation signal to produce a bandlimited echo corrected microphone signal, and
attenuating said bandlimited echo corrected microphone signal during periods of time during which said bandlimited echo corrected microphone signal is substantially derived from acoustic feedback between said loudspeaker and microphone.

2 more elements

A method for reducing the effects of acoustic feedback between loudspeaker and microphone in a communication system, comprising the steps of:

separating a near end microphone signal into a plurality of bandlimited microphone signals,
separating a loudspeaker signal into a plurality of bandlimited loudspeaker signals, the band of frequencies of each bandlimited loudspeaker signal being approximately the same as the band of frequencies of a corresponding bandlimited microphone signal,
applying each echo bandlimited loudspeaker signal to a corresponding adaptive echo estimator which in response generates an echo estimation signal, each said echo estimation signal representing an approximation of the acoustic feedback of said bandlimited loudspeaker signal into a corresponding bandlimited microphone signal,
subtracting an echo estimation signal from an associated bandlimited microphone signal having the same frequency band as said echo estimation signal, to produce a bandlimited echo corrected microphone signal,
identifying periods of time during which said near end microphone signal is substantially derived from acoustic feedback between said loudspeaker and microphone, and
adjusting characteristics of at least one said adaptive echo estimator during said identified periods of time.

3 more elements

Dependencies are inferred from the claim text.

Adaptive acoustic echo canceller having means for reducing or eliminating echo in a plurality of signal bandwidths

Life of this patent

Adaptive acoustic echo canceller having means for reducing or eliminating echo in a plurality of signal bandwidths

Life of this patent

Abstract

Claims40