Echo cancellation

• US 6,931,123 B1
• Filed: 04/07/1999
• Issued: 08/16/2005
• Est. Priority Date: 04/08/1998
• Status: Expired due to Fees

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Hughes, Peter James
• Primary Examiner(s): Barnie, Rexford
• Application Number:
  US09/623,979
• Time in Patent Office: 2,323 Days
• Field of Search: 379/406.01, 379/406.08, 379/406.06, 379/406.02, 379/392.01, 379/406.05, 379/406.12, 379/406.13, 379/406.14, 379/391, 379/388.07, 379/417, 381/80, 381/99, 381/94.1, 381/93, 381/11, 381/13, 381/82, 381/83, 381/92, 381/95, 370/286, 370/287, 370/289, 370/290, 370/291, 370/292, 455/570
• US Class Current: 379/406.01
• CPC Class Codes: H04M 3/002 Applications of echo suppressors or cancellers in telephonic connections in two-way loud-speaking telephone systems H04M9/08, echo suppressors or cancellers per se H04B3/20
• CPC Class Codes: H04M 3/56 Arrangements for connecting several subscribers to a common circuit, i.e. affording conference facilities video conference systems H04N7/15
• CPC Class Codes: H04M 3/567 Multimedia conference systems
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23
• CPC Class Codes: H04R 27/00 Public address systems circuits for preventing acoustic reaction H04R3/02; circuits for distributing signals to loudspeakers H04R3/12; monitoring or testing arrangements for public address systems H04R29/007; amplifiers H03F
• CPC Class Codes: H04R 3/02 for preventing acoustic reaction , i.e. acoustic oscillatory feedback specially adapted for hearing aids H04R25/453

Abstract

An audio conferencing system in which each participant in the conference generates a monaural signal for transmission on an output channel to the other participants, and receives a plurality of input channels from the other participants. The input channels are individually converted to stereophonic signal pairs by respective filter banks having selected predetermined transfer functions. The stereo channels are combined linearly to provide a stereophonic audio output. The system has an echo cancellation system in which an adaptive filter process is applied to the input channels to generate a combined echo cancellation signal for applying to the output channel.

Claims

1. A method of echo cancellation for an audio conferencing system in which a participant in the conference generates a monaural signal for transmission on an output channel to the other participants, and receives a monaural input channel from each of the other participants, the input channels being combined linearly to provide a spatialised audio output comprising a plurality of audio channels, characterised in that an adaptive filter process is applied to each of the input channels to generate a combined echo cancellation signal for applying to the output channel;

in which a separate adaptive filter is provided for each input channel, and the outputs of the filters are linearly combined to form the cancellation signal; and

input signals carried by the input channels are individually converted to spatialised signal sets by respective filter banks having selected predetermined transfer functions, wherein the adaptive filters are multiple channel filters, and correlations between the spatialised signal sets are allowed for by an adaptation process driven by data selected according to the selected transfer functions.

2. A method of echo cancellation for an audio conferencing system according to claim 1 in which the method is applied to a transaural spatialisation system.

3. A method of echo cancellation for an audio conferencing system according to claim 1 in which the method is applied to a panned stereo spatialisation system.

4. A method of echo cancellation for an audio conferencing system according to claim 1 in which the method is applied to an ambisonic spatialisation system.

5. Echo cancellation apparatus for an audio conferencing system having a monaural output channel and a plurality of monaural input channels, the input channels being combined linearly to provide a spatialised audio output comprising a plurality of audio channels, characterised in that an adaptive filter is applied to each of the input channels for generating an echo cancellation signal for applying to the output channel;

in which a separate adaptive filter is provided for each input channel, and the outputs of the filters are connected to a linear combiner to form the cancellation signal; and

the adaptive filters are multiple channel filters for operating on spatialised signal sets derived from respective input signals carried by the input channels according to respective predetermined transfer functions; and

an adaptation processor driven by knowledge of each transfer function is provided for controlling the adaptive filters to allow for correlations between the spatialised signal sets.

6. An apparatus according to claim 5, wherein the apparatus is applied to a transaural spatialisation system.

7. An apparatus according to claim 5, wherein the apparatus is applied to a panned stereo system.

8. An apparatus according to claim 5, wherein the apparatus is applied to an ambisonic system.

9. A method of echo cancellation for an audio conferencing system, the method comprising:

generating a monaural signal for transmission on an output channel;

receiving respective signals on a plurality of independent monaural input channels;

linearly combining the signals received on the input channels to provide a spatialized audio output comprising a plurality of audio channels;

applying an adaptive filter process to all of the signals received on the input channels to generate a combined echo cancellation signal for applying to the output channel;

providing a separate adaptive filter for each input channel and linearly combining the outputs of the filters to form the echo cancellation signal; and

individually converting the signals received on the input channels to spatialized signal sets by respective filter banks having selected predetermined transfer functions, wherein the adaptive filters are multiple channel filters, and correlations between the spatialized signal sets are allowed for by an adaptation process driven by data selected according to the selected transfer functions.

10. A method of echo cancellation for an audio conferencing system according to claim 9 in which the method is applied to a transaural spatialisation system.

11. A method of echo cancellation for an audio conferencing system according to claim 9 in which the method is applied to a panned stereo spatialisation system.

12. A method of echo cancellation for an audio conferencing system according to claim 9 in which the method is applied to an ambisonic spatialisation system.

13. An echo cancellation apparatus for an audio conferencing system, the apparatus comprising:

a monaural output channel;

a plurality of monaural input channels which are combined linearly to provide a spatialized audio output comprising a plurality of audio channels; and

an adaptive filter which is applied to all of the input channels for generating an echo cancellation signal for applying to the output channel;

wherein a separate adaptive filter is operably coupled to each input channel, and the outputs of the filters are connected to a combiner to form the echo cancellation signal; and

the adaptive filters are multiple channel filters for operating on spatialized signal sets derived from input signals carried by respective input channels according to respective predetermined transfer functions; and

an adaptation processor driven by knowledge of each transfer function is provided for controlling the adaptive filters to allow for correlations between the spatialized signal sets.

14. The apparatus according to claim 13, wherein the apparatus is applied to a transaural spatialisation system.

15. The apparatus according to claim 13, wherein the apparatus is applied to a panned stereo system.

16. The apparatus according to claim 13, wherein the apparatus is applied to an ambisonic system.