US 5,400,394 A · Adaptive echo canceller for voice messaging system

Abstract

An apparatus and method for echo cancellation in voice-messaging and voice-response systems, to enhance recognition of received DTMF and voice signals, comprising an efficient software echo canceller using adaptive digital filtering techniques. The voice messaging system includes analog telephone line interface modules which provide digitized voice data to a digital signal processor (DSP) chip. A transmit data line and a receive data line are each coupled to a cancel module with a cancel filter and an adapt/window module with an adaptive digital filter. The cancel filter causes echo cancellation on the receive data line; the adapt/window module monitors buffered transmit data in non-real time, without directly causing cancellation to occur, and selectively transfers an adjacent window of filter coefficients to the cancel filter under control of an adaptation control coupled to the adapt/window module. The control identifies a plurality of frames meeting a power criterion and passes the frames to the adaptive filter, which adapts on taps in frame segments during all available DSP real time, using a "cycle steal" approach for testing whether additional DSP processor cycles are available to use for echo cancellation. A masked white noise burst may be used to initialize adaptation. A windowing function identifies the best taps of an adapted frame, and corresponding coefficients are copied or loaded into the cancel filter. All control parameters are configurable, enabling site-specific performance optimization.

Claims15

Dependent claims

A method of adaptive echo cancellation in a voice messaging or voice response system having a memory store, at least one digital signal processor, a digital voice data receive data line, a transmit data line, and an echo canceller apparatus comprising a digital adapt filter having a plurality of adapt filter coefficients, a digital cancel filter coupled to the adapt filter and an adaptation control means for controlling transfer of the adapt filter coefficients to the cancel filter, the method comprising the steps of:

identifying a successive quantity of voice data frames on the transmit data line which pass a power criterion and storing the frames in a buffer;
truncating a plurality of segments from each data frame, and for each segment, deriving adapt filter coefficients from a plurality of taps in each segment during all available computing cycles of the digital signal processor;
selecting successive adjacent windows of taps from the adapt filter coefficents and identifying by an energy level test the best window;
and
transferring adapt filter coefficients in the best window to the cancel filter.

2 more elements

A method for providing echo cancellation signals in a voice messaging or voice response system having a memory store and a mass storage device and at least one digital signal processor providing a receive data line and a transmit data line and being coupled to the memory store and the mass storage device, the method comprising the steps of:

coupling an adapt filter to the receive data line and to the transmit data line and to the digital signal processor;
coupling a cancel filter to the adapt filter;
identifying a successive plurality of data frames on the receive data line meeting a power criteria test;
storing the successive plurality of data frames in a convergence buffer in the memory store;
deriving a plurality of adapt filter coefficients from the successive plurality of data frames;
selecting successive windowed quantities of taps from each of the adapt filter coefficients;
identifying a best windowed quantity having the most signal energy of successive windowed quantities;
generating a delay value signal using the plurality of adapt filter coefficients;
transferring the delay value and a subset of the adapt filter coefficients corresponding to the best windowed quantity to the cancel filter;
and
generating a cancel echo signal proportional to a plurality of cancel filter coefficients.

8 more elements

A method for providing echo cancellation signals in a hybrid in a voice messaging or voice response system having a memory store, a mass storage device and at least one digital signal processor providing a receive data line and a transmit data line and being coupled to the memory store and the mass storage device, the method comprising the steps of:

coupling an adaptive finite impulse response filter to the receive data line and to the transmit data line and to the digital signal processor;
identifying a successive plurality of data frames on the transmit data line meeting a power criteria test;
storing the data frames in a buffer in the memory store;
deriving a plurality of adapt filter coefficients from the successive plurality of data frames;
selecting successive windowed quantities of taps from each of the adapt filter coefficients;
identifying a best windowed quantity having the most signal energy of the selected successive windowed quantities;
adjusting the adapt filter coefficients in response to differences between an output of the adaptive finite impulse response filter and a real echo signal on the receive data line;
generating a delay value;
transferring the delay value and a subset of the adapt filter coefficients corresponding to the best windowed quantity to a cancel filter;
generating a cancel echo signal proportional to cancel filter coefficients in the memory store;
and
mixing the cancel echo signal with the real echo signal.

9 more elements

Dependencies are inferred from the claim text.

Adaptive echo canceller for voice messaging system

Life of this patent

Adaptive echo canceller for voice messaging system

Life of this patent

Abstract

Claims15