Echo canceller with variable step-size control
AssigneeSemiconductor Components Industries, LLC
InventorsThi Hong Thu Nguyen, Kozo Okuda
Life of this patent
Estimating the term…
Abstract
An acoustic echo canceller (AEC) uses a simulated echo from an adaptive filter to cancel an actual echo from a real environment. The echo cancellation is optimal when the adaptive filter response accurately matches the environment response. This can be achieved by changing coefficients of the filter in a step-wise fashion until the filter is converged on a configuration that provides optimal results. The convergence of the filter can be negatively affected by interference due to a double talk event or by an event in which the environment is changed. The disclosed AEC is configured to respond to these disruptive events by adjusting a step-size of the adaptive algorithm used to change the coefficients.
Claims19
An audio system, comprising:
- a speaker configured to play a transmitted signal to an environment;
- a microphone configured to receive a received signal from the environment, the received signal including an echo of the transmitted signal;
- and
- an echo canceller configured to cancel the echo of the transmitted signal from the received signal, the echo canceller including:
- an adaptive filter configured to model the environment to generate an echo estimate, the echo estimate subtracted from the received signal to cancel the echo of the transmitted signal from the received signal, the adaptive filter configured to:
- detect an event that causes a loss of convergence of the adaptive filter, the detection based on a variance of the received signal and on a cross-correlation between the received signal and an echo-cancelled signal at an output of the echo canceller,
- determine, during the event, an active step size according to a finite state machine, and
- adjust the adaptive filter according to the active step size.
A method for echo cancellation comprising:
- receiving a received signal from an environment, the received signal including an echo of a transmitted signal;
- generating an echo estimate using an adaptive filter configured to model the environment;
- subtracting the echo estimate from the received signal to cancel the echo of the transmitted signal from the received signal;
- detecting an event that causes a loss of convergence of the adaptive filter, the detection based on a variance of the received signal and on a cross-correlation between the received signal and an echo-cancelled signal at an output of the echo canceller;
- determining, during the event, an active step size according to a finite state machine;
- and
- adjusting the adaptive filter according to the active step size.
An echo canceller for an acoustic device, the echo canceller comprising:
- a finite impulse response (FIR) filter having coefficients to generate an echo estimate that is an estimate of an echo generated by an environment;
- a coefficient calculation block configured to apply a normalized least means squared (NLMS) algorithm to adjust the coefficients of the FIR filter to minimize a difference between a response of the FIR filter and the response of an environment;
- and
- a step-size controller configured to adjust an active step size of the NLMS algorithm during an event according to a finite state machine, the event being a double talk event or an environment change event, wherein the finite state machine includes:
- a first state in which the active step size is zero;
- a second state in which the active step size is greater than a step size before the event;
- and
- a third state in which the active step size is less than the step size before the event.
Dependencies are inferred from the claim text.