US 5,473,686 A · Echo cancellation apparatus

Abstract

The length (or the number of taps) of an adaptive finite impulse response (AFIR) filter is continuously modified to produce optimal echo cancellation. In accordance with one illustrative embodiment, this modification is performed by increasing or decreasing the number of delayed samples which are used to generate an echo estimate. More specifically, the number of samples used to generate the echo estimate is determined by selecting a trial number of samples and operating the filter for a sufficient length of time to allow the tap weights in the filter to stabilize. The tap weights are then examined to determine whether the taps at the end on the filter contribute at least a first threshold amount to the echo estimate. If not, the number of samples used in the filter is reduced and the process repeated. If the taps at the end of the filter contribute more than a second threshold amount, the number of samples is increased and the process is repeated.

Claims40

Dependent claims

An apparatus for canceling acoustic and electrical echoes in a digitized audio signal, the apparatus comprising:

a digital filter for generating an output signal, the digital filter having a plurality of sequential sections, wherein each of the sections generates a section signal which contributes to the output signal;
and
adjustment apparatus responsive to an adjustment value determined using at least a first section signal generated by at least one of the plurality of sections, the adjustment apparatus modifying the length of the filter by changing the total number of said plurality of sections in the digital filter in response to a difference between the adjustment value and a threshold value, the adjustment apparatus modifying the filter length repeatedly over time with a minimum temporal separation between each modification that is dependent on a convergence constant of the filter.

An apparatus for canceling acoustic and electrical echoes in a digitized audio signal which includes a desired input signal plus echoes, the apparatus comprising:

a digital finite-impulse-response filter having a tapped delay line with a plurality of tap outputs, a plurality of multipliers, one of the plurality of multipliers connected to each tap output for generating a partial output equal to the each tap output multiplied by a variable coefficient value, a summer for summing all of the partial outputs to generate an output signal and means for adjusting the coefficient values to minimize a difference between the filter output signal and the desired input signal;
apparatus for applying the digitized audio signal to the tapped delay line;
and
apparatus responsive to a predetermined number of the partial outputs for disconnecting the predetermined number of partial outputs from the summer when the partial outputs fall below a threshold value.

1 more element

A speakerphone apparatus for processing a digitized audio input signal which includes a desired input signal plus acoustic echoes and for processing a digitized audio output signal which includes a desired output signal plus electrical echoes, the speakerphone apparatus comprising:

a first digital finite-impulse-response filter for canceling the acoustic echoes having a first tapped delay line with a first plurality of tap outputs, a first plurality of multipliers, one of the first plurality of multipliers connected to each of the first plurality of tap outputs for generating a first partial output equal to the each of the first plurality of tap outputs multiplied by one of a first plurality of variable coefficient values, a first summer for summing all of the first partial outputs to generate a first output signal and a first mechanism for adjusting the first plurality of coefficient values to minimize a difference between the first filter output signal and the desired input signal;
first apparatus responsive to a first predetermined number of the first filter partial outputs for disconnecting the first predetermined number of partial outputs from the first summer when the partial outputs fall below a first threshold value;
a second digital finite-impulse-response filter for canceling the electrical echoes having a second tapped delay line with a second plurality of tap outputs, a second plurality of multipliers, one of the second plurality of multipliers connected to each of the second plurality of tap outputs for generating a second partial output equal to the each of the second plurality of tap outputs multiplied by one of a second plurality of variable coefficient values, a summer for summing all of the second partial outputs to generate a second output signal and a second mechanism for adjusting the second plurality of coefficient values to minimize a difference between the second filter output signal and the desired output signal;
second apparatus responsive to a second predetermined number of the partial outputs for disconnecting the second predetermined number of partial outputs from the second summer when the second partial outputs fall below a second threshold value.

1 more element

A method for canceling acoustic and electrical echoes in a digitized audio signal which includes a desired input signal plus echoes, the method comprising the steps of:

A. applying the digitized audio signal to a digital finite-impulse-response filter having a tapped delay line with a plurality of tap outputs, a plurality of multipliers, one of the plurality of multipliers connected to each tap output for generating a partial output equal to the each tap output multiplied by a variable coefficient value, a summer for summing all of the partial outputs to generate an output signal and a mechanism for adjusting the coefficient values to minimize a difference between the filter output signal and the desired input signal;
B. monitoring the outputs from a predetermined number of partial outputs;
and
C. disconnecting the predetermined number of partial outputs from the summer when the predetermined number of partial outputs fall below a threshold value.

1 more element

Dependencies are inferred from the claim text.

Echo cancellation apparatus

Life of this patent

Echo cancellation apparatus

Life of this patent

Abstract

Claims40