Method and apparatus for reducing residual far-end echo in voice communication networks
AssigneeAT&T Corp.
InventorsPatrick M. Velardo, Jr., Woodson D. Wynn
Life of this patent
Estimating the term…
Abstract
A method and apparatus are described for reducing, in communication signals received by a local network from a remote network (FAR-IN signals), that energy content that is attributable to echoes of signals transmitted into the local network (NEAR-IN signals). This is achieved, in part, by generating a time-varying TEMPLATE signal which represents the smoothed energy content of NEAR-IN signals delayed according to the echo path and attenuated by an estimated echo transmission loss. A non-linear processor passes the FAR-IN signal substantially without attenuation if it exceeds the threshold derived at least in part from the TEMPLATE, but attenuates the FAR-IN signal if it lies within a defined range below the threshold.
Claims35
A method for processing FAR-IN communication signals received by a FIRST network from a SECOND network, thereby to reduce energy content that is attributable to echoes, returned by the SECOND network, of NEAR-IN signals that were placed in the FIRST network for transmission to the SECOND network, the method comprising:
- a) measuring a delay between the NEAR-IN signals and the arrival of corresponding echoes in the FAR-IN signals;
- b) processing a copy of the NEAR-IN signals to create a time-varying signal which represents the smoothed energy content of the NEAR-IN signals delayed by the measured delay and attenuated by an estimated transmission loss for echoes, said time-varying signal to be referred to as a TEMPLATE;
- c) in a non-linear processor, passing the FAR-IN signals substantially without attenuation if they exceed a threshold derived at least in part from the TEMPLATE;
- and
- d) in the non-linear processor, attenuating the FAR-IN signals if they lie within a defined range below said threshold.
A method for processing FAR-IN communication signals received by a local network from a remote network, thereby to reduce energy content that is attributable to echoes, returned by the remote network, of NEAR-IN signals that were placed in the local network for transmission to the remote network, the method comprising:
- a) measuring a delay between the NEAR-IN signals and the arrival of corresponding echoes in the FAR-IN signals;
- b) analyzing the FAR-IN signals into a plurality of frequency sub-band components to be referred to as FAR-IN sub-band signals, delaying the NEAR-IN signals by the measured delay, and analyzing the delayed NEAR-IN signals into a plurality of frequency sub-band components, to be referred to as NEAR-IN sub-band signals;
- c) processing a copy of each NEAR-IN sub-band signal to create a time-varying signal which represents the smoothed energy content of the NEAR-IN sub-band signal delayed by the measured delay and attenuated by an estimated transmission loss for echoes, said time-varying signal to be referred to as a TEMPLATE;
- d) in a non-linear processor, passing each FAR-IN sub-band signal substantially without attenuation if it exceeds a threshold derived at least in part from the corresponding TEMPLATE;
- e) in the non-linear processor, attenuating each FAR-IN sub-band signal if it lies within a defined range below the corresponding said threshold;
- and
- f) synthesizing the nonlinearly processed FAR-IN sub-band signals to form an echo-reduced fullband FAR-IN signal.
In a communication system that comprises a local network and a remote network, wherein a sender at a remote location places FAR SPEECH communication signals in the remote network for transmission to the local network, and the local network receives said signals as FAR-IN signals, a method for processing the FAR-IN signals, thereby to reduce energy content that is attributable to echoes, returned by the remote network, of NEAR-IN signals that were placed in the local network for transmission to the remote network, the method comprising:
- a) measuring a delay between the NEAR-IN signals and the arrival of corresponding echoes in the FAR-IN signals;
- b) testing for energy in the FAR-IN signals that is attributable to FAR SPEECH, setting a flag to a DENY state when said energy is detected, and setting the flag to a PERMIT state when said energy is not detected;
- c) analyzing the FAR-IN signals into a plurality of frequency sub-band components to be referred to as FAR-IN sub-band signals, delaying the NEAR-IN signals by the measured delay, and analyzing the delayed NEAR-IN signals into a plurality of frequency sub-band components, to be referred to as NEAR-IN sub-band signals;
- d) processing a copy of each NEAR-IN sub-band signal to create a time-varying signal which represents the smoothed energy content of the NEAR-IN sub-band signal delayed by the measured delay and attenuated by an estimated transmission loss for echoes, said time-varying signal to be referred to as a TEMPLATE;
- e) passing each FAR-IN sub-band signal through a non-linear processor substantially without attenuation if said FAR-IN sub-bond signal exceeds a threshold derived at least in part from the corresponding said TEMPLATE;
- f) passing each FAR-IN sub-band signal through the non-linear processor with attenuation if said signal lies within a defined range below the corresponding said threshold;
- and
- g) synthesizing the passed-through FAR-IN sub-band signals to form an echo-reduced fullband FAR-IN signal;
- wherein
- h) steps (c)-(g) are carried out only when the flag is set to the PERMIT state.
A method for reducing, in signals received by a local telephone user from a conference-communication device at a remote location, said received signals to be referred to as FAR-IN signals, that energy content that is attributable to echoes of the local user's voice that are returned to the local user due to incomplete echo cancellation in the conference-communication device, the method comprising:
- a) measuring a delay between signals transmitted into the telephone network by the local user, said transmitted signals to be referred to as NEAR-IN signals, and the arrival of corresponding echoes in the FAR-IN signals;
- b) processing a copy of the NEAR-IN signals to create a time-varying signal which represents the smoothed energy content of the NEAR-IN signals delayed by the measured delay and attenuated by an estimated transmission loss for echoes, said time-varying signal to be referred to as a TEMPLATE;
- c) in a non-linear processor, passing FAR-IN signals substantially without attenuation if they exceed a threshold derived at least in part from the TEMPLATE;
- and
- d) in the non-linear processor, attenuating FAR-IN signals if they lie within a defined range below the said threshold.
Apparatus for processing FAR-IN communication signals received by a local network from a remote network, thereby to reduce energy content that is attributable to echoes, returned by the remote network, of NEAR-IN signals that were placed in the local network for transmission to the remote network, comprising:
- a) means for measuring a delay between NEAR-IN signals and the arrival of corresponding echoes in the FAR-IN signals;
- b) means for analyzing the FAR-IN signals into a plurality of frequency sub-band components to be referred to as FAR-IN sub-band signals, delaying the NEAR-IN signals by the measured delay, and analyzing the delayed NEAR-IN signals into a plurality of frequency sub-band components, to be referred to as NEAR-IN sub-band signals;
- c) means for receiving a copy of each NEAR-IN sub-band signal and for processing each said copy to create a time-varying output signal, to be referred to as a TEMPLATE, which represents the smoothed energy content of the NEAR-IN sub-band signal delayed by the measured delay and attenuated by an estimated transmission loss for echoes;
- d) a non-linear processor, adapted to pass each FAR-IN sub-band signal substantially without attenuation if it exceeds a threshold derived at least in part from the corresponding TEMPLATE and to attenuate each FAR-IN sub-band signal if it lies within a defined range below the corresponding said threshold;
- and
- e) means for synthesizing the nonlinearly processed FAR-IN sub-band signals to form an echo-reduced fullband FAR-IN signal.
Apparatus for reducing, in signals received by a local telephone user from a conference-communication device at a remote location, said received signals to be referred to as FAR-IN signals, that energy content that is attributable to echoes of the local user's voice that are returned to the local user due to incomplete echo cancellation in the conference-communication device, comprising:
- a) means for measuring a delay between signals transmitted into the telephone network by the local user, said transmitted signals to be referred to as NEAR-IN signals, and the arrival of corresponding echoes in the FAR-IN signals;
- b) means for receiving a copy of the NEAR-IN signals and for processing said copy to create a time-varying output signal, to be referred to as a TEMPLATE, which represents the smoothed energy content of the NEAR-IN signals delayed by the measured delay and attenuated by an estimated transmission loss for echoes;
- and
- c) a non-linear processor, adapted to pass FAR-IN signals substantially without attenuation if they exceed a threshold derived at least in part from the TEMPLATE and to attenuate FAR-IN signals if they lie within a defined range below the said threshold.
A communication system, comprising a FIRST network and a SECOND network connected through a communication medium, wherein NEAR-IN communication signals are placed in the FIRST network for transmission to the SECOND network, and FAR-IN communication signals are received by the FIRST network from the SECOND network;
- and further comprising apparatus for processing the FAR-IN signals, thereby to reduce energy content that is attributable to echoes, returned by the SECOND network, of NEAR-IN signals, wherein said communication system comprises:
- a) means for measuring a delay between NEAR-IN signals and the arrival of corresponding echoes in the FAR-IN signals;
- b) means for receiving a copy of the NEAR-IN signals and for processing said copy to create a time-varying output signal, to be referred to as a TEMPLATE, which represents the smoothed energy content of the NEAR-IN signals delayed by the measured delay and attenuated by an estimated transmission loss for echoes;
- and
- c) a non-linear processor adapted to pass FAR-IN signals substantially without attenuation if they exceed a threshold derived at least in part from the TEMPLATE and to attenuate FAR-IN signals if they lie within a defined range below the said threshold.
In a communication system that comprises FIRST and SECOND networks connected by a transmission medium, wherein NEAR-IN communication signals are placed in the FIRST network for transmission to the SECOND network, and FAR-IN communication signals are received by the FIRST network from the SECOND network, a method for detecting echoes of NEAR-IN signals that are returned to the FIRST network by the SECOND network, the method comprising:
- evaluating a frequency-domain coherence metric C(.tau.;f) of the NEAR-IN and FAR-IN signals, said metric a function of frequency f and of a relative delay .tau. between said signals;
- summing said metric C(.tau.;
- f) over a frequency band of interest, whereby a coherence-energy function C(.tau.) is obtained;
- and
- identifying a local peak value of said function C(.tau.).
Apparatus for detecting echoes in a communication system that comprises FIRST and SECOND networks connected by a transmission medium, wherein NEAR-IN communication signals are placed in the FIRST network for transmission to the SECOND network, and FAR-IN communication signals are received by the FIRST network from the SECOND network, and wherein said echoes are echoes of NEAR-IN signals that are returned to the FIRST network by the SECOND network, the apparatus comprising:
- means for evaluating a frequency-domain coherence metric C(.tau.;
- f) of the NEAR-IN and FAR-IN signals, said metric a function of frequency f and of a relative delay .tau. between said signals;
- means for summing said metric C(.tau.;
- f) over a frequency band of interest, whereby a coherence-energy function C(.tau.) is obtained;
- and
- means for identifying a local peak value of said function C(.tau.).
Dependencies are inferred from the claim text.