Adaptive filter for use in echo reduction

An adaptive filter comprising:

• an adder having a non-inverting input coupled to an output of a network element, wherein the network element has a transfer function;
• a signal estimator for estimating the transfer function, wherein an estimated signal output by the signal estimator is coupled to an inverting input of the adder, and the signal estimator has an input coupled to an error signal output of the adder, and wherein the signal estimator comprises;
• a coefficient threshold calculator for calculating a coefficient threshold;
• a first step size update processor that uses a first step size and an error signal at the error signal output for updating first filter coefficients of a plurality of filter coefficients, wherein the first filter coefficients have a magnitude less than the coefficient threshold;
• and
• a second step size update processor that uses a second step size and the error signal at the error signal output for updating second filter coefficients of the plurality of filter coefficients, wherein the second filter coefficients have a magnitude greater than the coefficient threshold.

A system for reducing an echo signal comprising:

• a first adaptive filter having a first input for receiving a signal output from a network element, a second input for receiving a signal input into the network element, a third input for receiving pure delay information, and an output for outputting a signal having reduced echo;
• a pure delay calculator for calculating the pure delay information, wherein the pure delay calculator has a first input for receiving the signal output from the network element, a second input for receiving the signal input into the network element, and an output coupled to the third input of the first adaptive filter for transferring the pure delay information;
• and
• a second adaptive filter in the pure delay calculator, wherein the second adaptive filter comprises:
• an adder having a non-inverting input for receiving the signal output from the network element, wherein the network element has a transfer function;
• a signal estimator for estimating the transfer function, wherein an estimated signal output by the signal estimator is coupled to an inverting input of the adder, and the signal estimator has an input coupled to an error signal output of the adder, and wherein the signal estimator comprises:
• a coefficient threshold calculator for calculating a coefficient threshold;
• a first step size update processor that uses a first step size and an error signal at the error signal output for updating first filter coefficients of a plurality of filter coefficients, wherein the first filter coefficients have a magnitude less than the coefficient threshold;
• and
• a second step size update processor that uses a second step size and the error signal at the error signal output for updating second filter coefficients of the plurality of filter coefficients, wherein the second filter coefficients have a magnitude greater than the coefficient threshold.