Update gain normalization is employed in adaptive filters to control weighting of the filter impulse response updates in order to converge properly to a desired impulse response. Singing, i.e., oscillating, of the filter is overcome by adjusting the update gain when an incoming signal power estimate used to normalize the gain exceeds a prescribed threshold value. In one example, the normalized gain is adjusted to be a fixed value for power estimate values which exceed the threshold. In accordance with another aspect of the invention, a single normalized gain value is used to adjust the update gain in two adaptive filters employed as echo cancelers in a bidirectional voice frequency repeater.

An echo-canceling system and method uses an echo estimate to modify the error signal which is obtained by the difference between an echo signal and the echo estimate. The modified error signal, rather than the error signal itself, is transmitted. By using the echo estimate as a parameter for modifying the error signal, improved hands-free performance may be obtained in a vehicular radiotelephone, such as a cellular telephone. Preferably, modification of the electrical error signal is performed by a center clipper which removes a portion of the electrical error signal which is below a variable threshold, wherein the variable threshold is determined by the echo estimate electrical signal. The variable threshold may be produced from the echo estimate electrical signal using an envelope detector.

An echo canceler has its otherwise conventional tapped delay line basis functions augmented with at least one pair of basis functions realizing two quadrature responses of a complex pole. The frequency of this complex pole is selected as substantially equal to the frequency of the dominant pole of a highpass filter inserted into the echo path of the echo canceler, where the dominant pole is the pole closest to the unit circle. This echo canceler arrangement results in a substantial improvement in attainable echo-return-loss enhancement (ERLE).

An input signal is supplied to a tapped-delay line adaptive filter to produce tap signals which are equally divided into groups. The tap signals are selectively coupled on a per group basis through a switch to coefficient generators where tap-weight coefficients are produced. The selected tap signals are weighted respectively by the coefficients and summed together to produce a correction signal, which is combined with an output signal which is a replica of the input signal. The coefficients are updated with a residual error of the correction signal. Using the coefficients, the hopping order for selecting a tap group and the dwell time of the tap group are determined. Total power of the selected tap signals is monitored. When the monitored power is lower than a threshold value, the determination of the hopping order and dwell time is disabled, coefficient updating is disabled, and the residual error is nullified for fast convergence.

A method for adaptation to an echo location in an echo canceller comprising an output port, an input port, an adjustable delay unit (43) compensating for the pure delay component in the echo path between the echo location and the output port of the echo canceller, a digital filter (40) calculating, from a signal outgoing to the echo path, an echo location estimate which is shorter than the maximum allowed duration of the echo path. The echo location is determined by calculating the echo path location at which there is a high correlation between the signal outgoing to the echo path and the returned echo. The correlation is calculated in a sliding window having the length of the digital filter.