Method and apparatus for echo cancellation

An echo cancellation circuit for a voice interaction device simultaneously outputting a remote signal while receiving a local signal, wherein the local signal comprises an echo generated from the remote signal, the echo cancellation circuit comprising:

• a first filter, learning the remote signal at a first speed to generate a first coefficient set, and the first coefficient set filtering the local signal to generate a first filter output;
• a second filter, learning the remote signal at a second speed to generate a second coefficient set, and the second coefficient set filtering the local signal to generate a second filter output;
• and
• a third filter, comprising a third coefficient set, canceling the echo from the local signal to generate a third filter output as an echo cancellation result;
• wherein a controller updates the third coefficient set based on the first, second and third filter outputs;
• wherein
• the controller detects remote talk, local talk and double talk according to the remote and local signals, and adjusts the second speed based on the detection result;
• the first and second speeds are individually determined by a first step size and a second step size;
• when the controller detects double talk, the controller reduces the second step size;
• when the controller detects no double talk, the controller increases the second step size;
• wherein the second step size does not exceed the first step size;
• the controller detects remote talk if the energy of remote signal exceeds a remote threshold;
• the controller detects local talk if the energy of local signal exceeds a local threshold;
• when no double talk is detected, the controller further sets the second step size by the following condition:
• if both remote talk and local talk exist, the controller sets the second step size to a first value lower than the first step size;
• if only remote talk exists, the controller sets the second step size to a second value lower than the first value;
• if only local talk exists, the controller sets the second step size to a third value lower than or equal to the second value;
• the first filter is a shadow filter recursively updating the first coefficient set based on a normalized least mean square (NLMS) algorithm;
• and
• the second filter is an adaptive filter recursively updating the second coefficient set based on the NLMS algorithm.

An echo cancellation circuit for a voice interaction device simultaneously outputting a remote signal while receiving a local signal, wherein the local signal comprises an echo generated from the remote signal, the echo cancellation circuit comprising:

• a first filter, learning the remote signal at a first speed to generate a first coefficient set, and the first coefficient set filtering the local signal to generate a first filter output;
• a second filter, learning the remote signal at a second speed to generate a second coefficient set, and the second coefficient set filtering the local signal to generate a second filter output;
• and
• a third filter, comprising a third coefficient set, canceling the echo from the local signal to generate a third filter output as an echo cancellation result;
• wherein a controller updates the third coefficient set based on the first, second and third filter outputs;
• wherein
• the controller detects remote talk, local talk and double talk according to the remote and local signals, and adjusts the second speed based on the detection result;
• the controller determines whether to update the third coefficient set according to energy levels of the first, second and third filter outputs, referred to as a first, a second, and a third energy;
• if the first energy is lower than a first ratio of the third energy, and lower than the second energy, the controller copies the first coefficient set to the third coefficient set;
• if the second energy is lower than a second ratio of the third energy, and lower than the first energy, the controller copies the second coefficient set to the third coefficient set;
• otherwise the third coefficient set remains as is;
• and
• the first and second ratios are values between 0 and 1.

An echo cancellation method, for a voice interaction device simultaneously outputting a remote signal while receiving a local signal, wherein the local signal comprises an echo generated from the remote signal, the echo cancellation method comprising:

• learning the remote signal at a first speed to generate a first coefficient set;
• filtering the local signal by the first coefficient set to generate a first filter output;
• learning the remote signal at a second speed to generate a second coefficient set;
• filtering the local signal by the second coefficient set to generate a second filter output;
• providing a third coefficient set to cancel the echo from the local signal to generate a third filter output as an echo cancelled result, wherein the third coefficient set is selectively a copy of the first or second coefficient set decided by comparison of the first, second and third filter outputs;
• detecting remote talk, local talk and double talk according to the remote and local signals, and adjusting the second speed based on the detection result;
• wherein the first and second learning speeds are individually determined by a first step size and a second step size;
• and the echo cancellation method further comprising:
• when double talk is detected, reducing the second step size;
• when no double talk is detected, increasing the second step size;
• wherein the second step size does not exceed the first step size;
• detecting remote talk if the energy of remote signal exceeds a remote threshold;
• detecting local talk if the energy of local signal exceeds a local threshold;
• and
• when no double talk is detected, setting the second step size by:
• if both the remote talk and local talk exist, setting the second step size to a first value lower than the first step size;
• if only the remote talk exists, setting the second step size to a second value lower than the first value;
• and
• if only the local talk exists, setting the second step size to a third value lower than or equal to the second value.

An echo cancellation method, for a voice interaction device simultaneously outputting a remote signal while receiving a local signal, wherein the local signal comprises an echo generated from the remote signal, the echo cancellation method comprising:

• learning the remote signal at a first speed to generate a first coefficient set;
• filtering the local signal by the first coefficient set to generate a first filter output;
• learning the remote signal at a second speed to generate a second coefficient set;
• filtering the local signal by the second coefficient set to generate a second filter output;
• providing a third coefficient set to cancel the echo from the local signal to generate a third filter output as an echo cancelled result, wherein the third coefficient set is selectively a copy of the first or second coefficient set decided by comparison of the first, second and third filter outputs;
• determining whether to update the third coefficient set according to energy levels of the first, second and third filter outputs, referred to as a first, a second, and a third energy;
• if the first energy is lower than a first ratio of the third energy, and lower than the second energy, copying the first coefficient set to the third coefficient set;
• if the second energy is lower than a second ratio of the third energy, and lower than the first energy, copying the second coefficient set to the third coefficient set;
• and
• otherwise leaving the third coefficient set as is;
• wherein
• the first and second ratios are values between 0 and 1.