Determining an acoustic coupling between a far-end talker signal and a combined signal
An improved determination of an acoustic coupling between a loudspeaker and a microphone, which results in a better estimate of the acoustic coupling during double talk, is achieved in a device for determining an acoustic coupling between a far-end talker signal as produced by the loudspeaker and a combined signal as picked up by the microphone. The combined signal comprises an echo of the far-end talker signal and a near-end talker signal. The acoustic coupling is derived from a ratio of changes in an envelope of the combined signal to changes in the envelope of the far-end talker signal in a predetermined time interval. In this way, a systematic error during double talk is strongly reduced.
1. A device for determining an acoustic coupling between a far-end talker signal and a combined signal that comprises an echo of the far-end talker signal and a near-end talker signal, the device comprising:
inputs for receiving the far-end talker signal and the combined signal; and
circuitry for deriving the acoustic coupling from a ratio of changes in an envelope of the combined signal to changes in an envelope of the far-end talker signal in a predetermined time interval,
wherein the circuitry comprises an adaptive filter and a subtractor, the adaptive filter being configured to filter the changes in the envelope of the far-end talker signal, and the subtractor being configured to determine a residual signal by calculating a difference between an output signal of the adaptive filter and the changes in the envelope of the combined signal, wherein the adaptive filter is controlled by the residual signal to adjust coefficients of the adaptive filter in such a way that an energy of the residual signal is minimized, and wherein the residual signal is provided to the adaptive filter for adjusting the coefficients of the adaptive filter, and
wherein the circuitry further comprises a first changes-in-envelope determining circuit for determining changes in the envelope of the far-end talker signal and a second changes-in-envelope determining circuit for determining changes in the envelope of the combined signal.
2. The device as claimed in claim 1 , wherein the envelope of the combined signal and the envelope of the far-end talker signal are obtained from the combined signal by rectifying and averaging on a block basis and the far-end talker signal by rectifying and averaging on the block basis, respectively.
3. The device as claimed in claim 1 , wherein the predetermined time interval is a time interval between successive samples of the far-end talker signal, wherein sampling of the combined signal is aligned with sampling of the far-end talker signal.
4. The device as claimed in claim 1 , wherein the predetermined time interval comprises a multiplicity of a time interval between successive samples of the far-end talker signal, wherein sampling of the combined signal is aligned with sampling of the far-end talker signal.
5. The device as claimed in claim 1 , wherein a coefficient of the adaptive filter is the ratio of the changes in the envelope of the combined signal to the changes in the envelope of the far-end talker signal in the predetermined time interval.
6. The device as claimed in claim 5 , wherein the adaptive filter is a multi-tap filter, wherein the ratio of the changes in the envelope of the combined signal to the changes in the envelope of the far-end talker signal in the predetermined time interval is determined as a coefficient of the adaptive filter having a largest value.
7. The device as claimed in claim 6 , wherein a delay between a far-end talker signal and the echo of the far-end talker signal is determined by a location of a tap with the largest value of the coefficient of the adaptive filter that determines the acoustic coupling.
8. A method for determining an acoustic coupling between a far-end talker signal and a combined signal that comprises an echo of the far-end talker signal and a near-end talker signal, the method comprising acts of:
providing the far-end talker signal and the combined signal to a processing device; and
deriving by the processing device the acoustic coupling from a ratio of changes in an envelope of the combined signal to changes in an envelope of the far-end talker signal in a predetermined time interval,
wherein the deriving includes acts of:
determining by a first changes-in-envelope determining circuit of the processing device changes in the envelope of the far-end talker signal;
determining by a second changes-in-envelope determining circuit of the processing device changes in the envelope of the combined signal;
filtering by an adaptive filter the changes in the envelope of the far-end talker signal, wherein the adaptive filter is controlled by a residual signal to adjust coefficients of the adaptive filter in such a way that an energy of the residual signal is minimized, and wherein the residual signal is provided to the adaptive filter for adjusting the coefficients of the adaptive filter; and
subtracting by a subtractor a difference between an output signal of the adaptive filter and the changes in the envelope of the combined signal to determine the residual signal.
9. The method of claim 8 , wherein a coefficient of the adaptive filter is the ratio of the changes in the envelope of the combined signal to the changes in the envelope of the far-end talker signal in the predetermined time interval.
10. An acoustic echo canceller comprising:
a loudspeaker for reproducing a far-end talker signal;
a microphone for picking-up a combined signal that comprises an echo of the far-end talker signal and a near-end talker signal;
a device for determining an acoustic coupling signal between the far-end talker signal and the combined signal, the device including a first filter for outputting the acoustic coupling signal;
a second filter for filtering the far-end talker signal in dependence on a difference between an output signal of the adaptive filter and changes in an envelope of the combined signal to predict the echo on the microphone caused by the loudspeaker; and
wherein the device further includes: inputs for receiving the far-end talker signal and the combined signal; and
circuitry for deriving the acoustic coupling from a ratio of the changes in the envelope of the combined signal to changes in an envelope of the far-end talker signal in a predetermined time interval,
wherein the second filter is configured to filter the changes in the envelope of the far-end talker signal, wherein the second filter is controlled by the acoustic coupling signal and by a residual signal to adjust coefficients of the adaptive filter in such a way that an energy of the residual signal is minimized, wherein the residual signal is provided to the second filter for adjusting the coefficients of the second filter, and wherein the residual signal is determined by a subtractor, the subtractor calculating the difference between the output signal of the second filter and the changes in the envelope of the combined signal, and
wherein the circuit co rises a first changes-in-envelope determining circuit for determining changes in the envelope of the far-end talker signal and a second changes-in-envelope determining circuit for determining changes in the envelope of the combined signal.
11. The acoustic echo canceller of claim 10 , further comprising:
a delay circuit preceding the echo filter to delay the far-end talker signal,
wherein the delay circuit is controlled by location of a tap with a largest value of the second filter that determines the acoustic coupling.
12. The acoustic echo canceller of claim 10 , wherein a coefficient of the second filter is the ratio of the changes in the envelope of the combined signal to the changes in the envelope of the far-end talker signal in the predetermined time interval.