Updating filter coefficients during echo cancellation
Updating filter coefficients during echo cancellation is disclosed. In some embodiments, a communication device may include a processor configured to operate a background filter configured as an adaptive filter, operate a foreground filter configured as a fixed filter; and update the foreground filter with coefficients from the background filter responsive to monitoring a history of both a near-end signal energy and an estimated far-end signal energy for a pre-determined time window in which conditions of each of the near-end signal energy and the estimated far-end signal energy are satisfied.
1. A communication device, comprising:
a microphone configured to capture sound; and
a computing system communicatively coupled to the microphone and configured to cause the communication device to perform operations, the operations comprising:
operate, during a particular period of time, a background filter configured as an adaptive filter and configured to generate an estimated far-end signal based on:
background filter coefficients of the background filter that are updated during the particular period of time,
a near-end signal generated by the communication device based on the sound captured by the microphone, and
a line-in signal that includes:
a far-end signal obtained by the communication device over a network; and
an echo signal that includes an echo of the near-end signal;
determine that the near-end signal is active during the particular period of time;
determine that the far-end signal is inactive during the particular period of time based on the estimated far-end signal; and
update foreground filter coefficients of a foreground filter with the background filter coefficients in response to determining that the near-end signal is active during the particular period of time and in response to determining that the far-end signal is inactive during the particular period of time, the foreground filter being configured to generate an echo cancelled signal based on the line-in signal, the near-end signal, and the foreground filter coefficients.
2. The communication device of claim 1 , wherein:
determining that the near-end signal is active during the particular period of time is based on a first number of times, during the particular period of time, that near-end signal energy of the near-end signal is above a first energy threshold, and
determining that the far-end signal is inactive during the particular period of time is based on a second number of times, during the particular period of time, that estimated far-end energy of the estimated far-end signal is below a second energy threshold.
3. The communication device of claim 2 , wherein:
determining that the near-end signal is active during the particular period of time is in response to the first number of times satisfying a first count threshold, and
determining that the far-end signal is inactive during the particular period of time is in response to the second number of times satisfying a second count threshold.
4. The communication device of claim 3 , wherein the first count threshold is based on a first fraction of the particular period of time.
5. The communication device of claim 3 , wherein the second count threshold is based on a second fraction of the particular period of time.
6. The communication device of claim 1 , wherein the background filter is a recursive least squared (RLS) adaptive filter.
7. The communication device of claim 6 , wherein the RLS adaptive filter implements an algorithm selected from a group consisting of: a covariance-matrix-based RLS algorithm and its square root versions that use a tapped-delay line parameterization and a matrix inversion lemma; an order-recursive RLS algorithm that uses a lattice structure for filter parameterization and error computation; and a fast fixed-order RLS algorithm.
8. The communication device of claim 6 , wherein the operations further comprise: operate a state machine to control the RLS adaptive filter and to update the foreground filter with coefficients from the background filter.
9. The communication device of claim 8 , wherein the state machine controls an amplitude control block of the near-end signal after updating of the foreground filter coefficients has been initiated.
10. A method for cancelling echo, the method comprising:
monitoring, during a particular period of time, near-end signal energy of a near-end signal generated by a communication device based on sound captured by a microphone of the communication device;
monitoring, during the particular period of time, an estimated far-end signal energy of an estimated far-end signal that is an output of a background filter in which the output is based on the near-end signal and in which the estimated far-end signal is an estimate of a far-end signal obtained by the communication device from a far-end device during a communication session;
determining, based on the monitoring of the near-end signal energy, that the near-end signal is active during the particular period of time;
determining, based on the monitoring of the estimated far-end signal energy, that the far-end signal is inactive during the particular period of time;
updating foreground filter coefficients of a foreground filter with background filter coefficients of the background filter in response to determining that the near-end signal is active during the particular period of time and in response to determining that the far-end signal is inactive during the particular period of time; and
performing, by the foreground filter, an echo cancellation on an input signal that includes the far-end signal and an echo signal that includes an echo of the near-end signal.
11. The method of claim 10 , wherein determining that the near-end signal is active during the particular period of time is based on a first number of times, during the particular period of time, that the near-end signal energy satisfies a relationship criterion with respect to a first energy threshold.
12. The method of claim 11 , wherein determining that the near-end signal is active during the particular period of time is in response to the first number of times satisfying a first count threshold value.
13. The method of claim 12 , wherein the first count threshold value is based on a first fraction of the particular period of time.
14. The method of claim 12 , wherein the first number of times that the near-end signal energy satisfies the relationship criterion with respect to the first energy threshold is a number of samples of the near-end signal energy that are above the first energy threshold during the particular period of time, and determining that the near-end signal is active during the particular period of time is in response to the first number of times being greater than the first count threshold value.
15. The method of claim 12 , wherein the first number of times that the near-end signal energy satisfies the relationship criterion with respect to the first energy threshold is a number of samples of the near-end signal energy that are below the first energy threshold during the particular period of time, and determining that the near-end signal is active during the particular period of time is in response to the first number of times being less than the first count threshold value.
16. The method of claim 10 , wherein determining that the far-end signal is inactive during the particular period of time is based on a second number of times, during the particular period of time, that the estimated far-end signal energy satisfies a relationship criterion with respect to a second energy threshold.
17. The method of claim 16 , wherein the second number of times that the estimated far-end signal energy satisfies the relationship criterion with respect to the second energy threshold is how many times during the particular period of time that the estimated far-end signal energy is below the second energy threshold.
18. The method of claim 16 , wherein the second number of times that the estimated far-end signal energy satisfies the relationship criterion with respect to the second energy threshold is how many times during the particular period of time that the estimated far-end signal energy is above the second energy threshold.
19. One or more non-transitory computer-readable media configured to store instructions that, in response to being executed by a processor, cause a communication device to perform operations, the operations comprising:
determine that a near-end signal is active during a particular period of time, the near-end signal being generated by a communication device based on sound captured by a microphone of the communication device;
determine that a far-end signal is inactive during the particular period of time based on an estimated far-end signal that is an output of a background filter in which the output is based on the near-end signal and in which the estimated far-end signal is an estimate of the far-end signal, which is obtained by the communication device over a network;
update foreground filter coefficients of a foreground filter with background filter coefficients of the background filter in response to determining that the near-end signal is active during the particular period of time and in response to determining that the far-end signal is inactive during the particular period of time; and
perform, by the foreground filter, an echo cancellation on an input signal that includes the far-end signal and an echo signal that includes an echo of the near-end signal.
20. The one or more non-transitory computer-readable media of claim 19 , wherein:
determining that the near-end signal is active during the particular period of time is based on a first number of times, during the particular period of time, that near-end signal energy of the near-end signal is on one side of a first energy threshold; and
determining that the far-end signal is inactive during the particular period of time is based on a second number of times, during the particular period of time, that estimated far-end signal energy of the estimated far-end signal is on one side of a second energy threshold.