Efficient speakerphone anti-howling system

• US 5,646,990 A
• Filed: 09/21/1995
• Issued: 07/08/1997
• Est. Priority Date: 09/21/1995
• Status: Expired due to Term

• Current Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Original Assignee: Rockwell International Corporation
• Inventors: Li, Xu
• Primary Examiner(s): Zele, Krista M.
• Assistant Examiner(s): KUMAR, DEVENDRA
• Application Number:
  US08/531,993
• Time in Patent Office: 656 Days
• Field of Search: 379/388, 379/389, 379/390, 379/406, 379/409, 379/410, 379/411, 370/32.1
• US Class Current: 379/406.08
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23

Abstract

A cost-effective anti-howling system and method enables fast detection of the presence of true double talk, and substantially eliminates undesirable howling attributable to sudden changes in the acoustic echo path between a speakerphone microphone and loudspeaker during speakerphone conversations. Speakerphone embodiments include a delay-compensated and normalized cross-product calculation performed by a system processor having at least two memory buffers. One buffer is associated with the loudspeaker signal and the other buffer is associated with the microphone signal. The delay-compensated cross-product of the microphone voice signal input and the loudspeaker voice signal output is determined and normalized by energy estimates of the two signals to reduce the calculation error made by variance in the signal level.

Claims

1. A system for identifying and canceling the effects of acoustic coupling during telephone communications between a local user and a remote user, wherein transmit signals are input by the local user and receive signals are input by the remote user, the system comprising:

a first transducer for transmitting the transmit signals;

a second transducer situated near the first transducer for receiving and broadcasting the receive signals, wherein the proximity of the second transducer to the first transducer causes acoustic coupling having associated echo;

communication means for carrying the transmit and receive signals, the transmit and receive signals having representative transmit samples and receive samples, and transmit and receive signal energies, wherein the communication means includes a first node which receives the transmit samples, and a second node which receives the receive samples,

wherein the communication means determines a delay from when the receive samples are received at the second node to when the receive samples are broadcast by the second transducer, and from when the transmit samples are input by the local user to when the transmit samples are received at the first node;

correlation means for determining if the transmit samples received at the first node and the receive samples received at the second node are substantially correlated, the correlation means providing correlation information; and

a processor for processing the correlation information, such that if the correlation is high between the transmit samples and the receive samples, the processor determines that the transmit samples are similar to the receive samples and thus represent echo, and if the correlation is low, the processor concludes that the transmit samples represent input transmit signals from the local user.

2. The system of claim 1, further comprising means for canceling any howling attributable to transmit signal changes.

3. The system of claim 1, wherein the correlation means comprises a cross-product calculator in which a predetermined number of transmit samples and a predetermined number of receive samples, which are determined following the delay, are processed in conjunction with their respective transmit and receive signal energies to generate a cross-product value, further wherein the processor, processes the cross-product value to assist in determining the similarity between the transmit samples and the receive samples.

4. The speakerphone system of claim 3, wherein if the cross-product value is high and them is change in the transmit signal energy, the processor will determine that the change in the transmit signals is caused by movement of the microphone relative to the second transducer, and if the cross-product value is low, the processor will determine that the change in the transmit signals is caused by transmit signals being input by the local user.

5. A speakerphone system for canceling the effects of acoustic coupling during speakerphone communications between a local user and a remote user, wherein transmit signals are input by the local user and receive signals are input by the remote user, the system comprising:

a microphone for transmitting the transmit signals;

a loudspeaker situated near the microphone for receiving and broadcasting the receive signals, wherein the proximity of the loudspeaker to the microphone causes acoustic coupling having associated echo, further wherein the receive signals and transmit signals have an associated impulse response;

an echo canceller coupled to the microphone and loudspeaker;

at least one communication channel across which the transmit signals and the receive signals are directed, the transmit and receive signals having representative transmit samples Bm and receive samples Bs, and transmit and receive signal energies, respectively, the at least one communication channel including a Node B which receives the transmit samples and a Node C which receives the receive samples,

wherein the speakerphone system has a first delay from when the receive samples are received at Node C to when the receive samples are broadcast by the loudspeaker, and a second delay defined between when the transmit samples are input by the local user to when the transmit samples are received at Node B, further wherein the first delay added to the second delay is called DLY;

a microphone buffer for storing transmit samples Bm(1) to Bm(Ln), where Bm(1) represents a first transmit sample stored in the microphone buffer, and Bm(Ln) represents transmit sample Ln stored in the microphone buffer;

a loudspeaker buffer for storing receive samples Bs(1) to Bs(DLY+Ln), where Bs(1) represents a first sample stored in the loudspeaker buffer, and Bs(DLY+Ln) represents transmit sample DLY+Ln stored in the loudspeaker buffer;

means for applying a cross-product function to the stored transmit and receive samples according to the equation;

##EQU3## where E_m and E_s represent the energies of the transmit and receive signals at Nodes B and C, respectively, wherein the means for applying a cross-product function has a cross-product output;

a speech detector for receiving the cross-product output; and

a controller coupled to the speech detector for processing the cross-product output relative to the transmit and receive signals to recognize changes in the transmit signals relative to the receive signals, and for determining whether the changes in the transmit signals are attributable to changes in acoustic coupling or to new transmit signals input into the microphone by the local user.

6. The speakerphone system of claim 5, wherein the echo canceller comprises an adaptive filter having corresponding filter coefficients which are adapted in accordance with the impulse response of the transmit and receive signals.

7. The speakerphone system of claim 6, wherein the communications between the local user and the remote user switch between a plurality of communication modes.

8. The speakerphone system of claim 7, wherein if the controller determines that the transmit signal changes are caused by acoustic coupling, the echo canceller will continue to adapt the filter coefficients and the communication mode is not switched.

9. The speakerphone system of claim 5, wherein if the cross-product output is high and the transmit signal energy suddenly changes, the controller will determine that the change in the transmit signals is caused by movement of the microphone relative to the loudspeaker, and if the cross-product output is low, the controller will determine that the change in the transmit signals is caused by transmit signals being input by the local user.

10. The speakerphone system of claim 5, further comprising energy estimation means for estimating the transmit and receive signal energies, wherein sample periods are defined for each transmit and receive sample, further wherein for each sample period, new energy estimates are determined according to:

##EQU4##

11. The speakerphone system of claim 5, wherein the receive samples Bs(1) to Bs(DLY) stored in the loudspeaker buffer are not used in the cross-product function.

12. A speakerphone system for canceling undesirable system howling between a local user using a local speakerphone system and a remote user, wherein local transmit signals are transmitted by the local user to the remote user, and remote receive signals are transmitted by the remote user to the local user, the speakerphone system comprising:

a microphone for transmitting the transmit signals to the remote user;

a loudspeaker for receiving and broadcasting the receive signals, the loudspeaker being acoustically coupled to the microphone, wherein the coupling of the microphone and loudspeaker defines an acoustic impulse response when broadcast receive signals are received and retransmitted by the microphone, the retransmitted signals representing echo;

speakerphone electronics coupled to the microphone including a processor for processing the transmit and receive signals, the processor comprising;

means for distinguishing the transmit signals from the broadcast receive signals,

means for calculating a delay between the broadcast receive signals and the echo of the broadcast receive signals; and

processor means for identifying changes in the acoustic impulse response between the microphone and loudspeaker, including correlation means for determining the correlation of the transmit signals and the receive signals, accounting for the calculated delay, wherein if the correlation means determines that the transmit signals and the receive signals are substantially correlated, the means for identifying will determine that the change in the acoustic impulse response is attributable to echo.

13. The system of claim 12, further comprising means for canceling the echo.

14. The system of claim 13, wherein the means for canceling the echo comprises an acoustic echo canceller (AEC) for detecting rebroadcast echo and for receiving the receive signals, such that the echo is canceled from the transmit signals.

15. A method of canceling the effects of acoustic coupling during telephone communications between a local user and a remote user, wherein transmit signals are input by the local user and receive signals are input by the remote user, the method comprising the steps of:

receiving the transmit signals and transmitting the transmit signals to the remote user;

receiving and broadcasting the receive signals, wherein acoustic coupling having associated echo is generated when transmit signals and receive signals are received simultaneously;

identifying representative transmit samples and receive samples among the transmit and receive signals, respectively;

receiving the transmit samples at a first node and the receive samples at a second node;

determining a delay including the time from when the receive samples are received at the second node to when the receive samples are broadcast, and the time from when the transmit samples are input to when the transmit samples are received at the first node;

estimating transmit and receive signal energies;

correlating the transmit samples received at the first node and the receive samples received at the second node to provide correlation information; and

processing the correlation information with a processor, such that if the correlation information indicates that the correlation is high between the transmit samples and the receive samples, the transmit samples are determined to be similar to the receive samples and thus represent echo, and if the correlation is low, the processor concludes that the transmit samples represent input transmit signals from the local user.

16. The system of claim 15, further comprising the step of preventing transmission of echo.

17. The system of claim 15, wherein the step of correlating comprises the steps of:

calculating a cross-product in which a predetermined number of transmit samples and a predetermined number of receive samples, which are determined following the defined delay, are processed in conjunction with their respective estimated transmit and receive signal energies to generate a cross-product value; and

processing the cross-product value to determine whether a change in the transmit signals is attributable to a sudden input of transmit signals by the local user, whereupon the transmit signals are not determined to be howling.

18. A system for identifying and canceling the effects of acoustic coupling during telephone communications between a local user and a remote user, wherein transmit signals are input by the local user and receive signals are input by the remote user, the system comprising:

a first transducer for transmitting the transmit signals;

a second transducer situated near the first transducer for receiving and broadcasting the receive signals, wherein the proximity of the second transducer to the first transducer causes acoustic coupling having associated echo;

communication means for carrying the transmit and receive signals, the transmit and receive signals having representative transmit samples and receive samples, and transmit and receive signal energies, wherein the communication means includes a first node which receives the transmit samples, and a second node which receives the receive samples;

correlation means for calculating a cross-product in which a predetermined number of transmit and receive signal samples are processed in conjunction with their respective transmit and receive signal energies to generate a cross-product value to determine if the transmit samples received at the first node and the receive samples received at the second node are substantially correlated, the correlation means providing correlation information; and

a processor for processing the correlation information, such that if the correlation is high between the transmit samples and the receive samples, the processor determines that the transmit samples are similar to the receive samples and thus represent echo, and if the correlation is low, the processor concludes that the transmit samples represent input transmit signals from the local user,

wherein if the cross-product value is high and there is change in the transmit signal energy, the processor will determine that the change in the transmit signals is caused by movement of the first transducer relative to the second transducer, and if the cross-product value is low the processor will determine that the change in the transmit signals is caused by transmit signals being input by the local user.

19. A method of canceling the effects of acoustic coupling during telephone communications between a local user and a remote user, wherein transmit signals are input by the local user and receive signals are input by the remote user, the method comprising the steps of:

receiving the transmit signals and transmitting the transmit signals to the remote user;

receiving and broadcasting the receive signals, wherein acoustic coupling having associated echo is generated when transmit signals and receive signals are received simultaneously;

identifying representative transmit samples and receive samples among the transmit and receive signals, respectively;

receiving the transmit samples at a first node and the receive samples at a second node;

estimating transmit and receive signal energies;

calculating a cross-product in which predetermined numbers of transmit and receive samples are processed in conjunction with their respective estimated transmit and receive signal energies to generate a cross-product value which represents correlation information; and

processing the correlation information with a processor, such that if the correlation information indicates that the correlation is high between the transmit samples and the receive samples, the transmit samples are determined to be similar to the receive samples and thus represent echo, and if the correlation is low, the processor concludes that the transmit samples represent input transmit signals from the local user,

wherein if the cross-product value is high and there is change Ln the transmit signal energy, the processor will determine that the change in the transmit signals is caused by movement of a first transducer relative to a second transducer, and if the cross-product value is low, the processor will determine that the change in the transmit signals is caused by transmit signals being input by the local user.