Lucent Technologies Inc.

At&t Bell Laboratories

Bell Telephone Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

American Telephone and Telegraph, Co.

Donald Lars Duttweiler

Christodoulos Chamzas

John Hartung

Cheng Kim

Barin Geoffry Haskell

Toshio Miki

Toshiro Kawahara

Dewayne Alan Spires

David G Shaw

Charles W Gritton

David Gavin Messerschmitt

Timothy James Zebo

Allan Michael Hofmann

Gerard Joseph Pepenella

Ying G Tao

Christosdoulos Chamzas

Lynn Emery Ditty

Nuri Ruhi Dagedeviren

Ying Get Tao

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).

Quadrature filter augmentation of echo canceler basis functions

A network-based CODEC (coder-decoder) includes an echo canceler. This CODEC recognizes the presence of a data call by detecting predefined signaling portions of a modem handshaking process. For each detected data call, the CODEC uses a stored channel model for performing echo cancellation during the data call. The CODEC trains off-line during selected segments of the modem call and then stores the new channel model for use in a future data call.

Echo cancellation in the network for data applications

A high order SINC interpolator and as a high order SINC decimator. The high order SINC interpolator includes an interpolator input and a plurality of cascades of integrators. The inputs of each of the cascades are coupled to the interpolator input through a low frequency delay circuit. The outputs of each of the cascades of integrators are coupled through a plurality of adders to generate a single interpolator output. The high order SINC decimator includes a decimator input and a plurality of cascades of integrators. The decimator input is coupled to the input of each of the cascades of the integrators. At least one low frequency delay circuit is coupled to an output of the cascades of the integrators and the output of each low frequency delay circuit is coupled to the decimator output through an adder.

High order SINC filter

Quantization noise, introduced into data transmission when analog signals are translated into PCM code using the logarithmic conversion of &mgr;-law or A-law rules necessary to accommodate the transmission of voice signals, limits the maximum attainable speed of data transmission. However, when the PCM code signals represent data (rather than voice signals), linear conversion of analog data signals into the PCM code would avoid such logarithmic quantization noise. To signal the translating codec that a digital modem call is being made, the digital modem allocates one or more of the least significant bit positions of the code representing the 2100 Hz answer-tone-with-phase-reversal (specified in ITU-T Recommendation G. 165) to send a repetitive pattern &ldquo;P &rdquo; to signal to the associated codec that a digital modem connection has been made. When the codec detects the P pattern it will linearly convert analog data signals into PCM code, thereby reducing the introduction of logarithmic quantization noise.

Data optimized codec

An adaptive filter and method that proportionately adjusts individual tap gain distributors such that the individually adjusted tap gains are not necessarily equal to one another and that the average of tap gains remains substantially constant. The filter employs a proportionate normalized least-means-squares (PNLMS) method of adaptation that imparts improved convergence speed over prior art adaptive filters that utilize a normalized least-means-squares (NLMS) method of adaptation, without affecting the adaptation quality of the filter.

Adaptive filter

A system and method for enhancing interactive communication between video conferencing devices of the type in which a delay is inserted into the audio transmission path to provide lip synchronization of the image and speech of the respective users thereof. Each video conferencing device includes a display device for displaying images of at least one communicating party and a speech communicating system for communicating with the communicating party. In accordance with one embodiment of the invention, a speech detecting circuit detects an utterance by a first user of a first video conferencing apparatus. An audible or visual indication is provided to at least a second user of a second video conferencing apparatus before the utterance is reproduced. As a result, the potential for simultaneous speaking by two or more users is substantially reduced. In an alternate embodiment, the amount of delay introduced into the audio signal transmission path is adjusted in accordance with the mode of operation of the video conferencing devices. An audio signal processing system detects, over predetermined intervals, whether or not an interactive conversation between two or more users is in progress. If an interactive conversation is not detected, lip synchronization proceeds in a conventional manner by introducing a predetermined delay into the audio path. If an interactive conversation is detected, the amount of audio delay inserted is minimized until there is a return to the lecture mode of operation.

Video conferencing system and method for providing enhanced interactive

The detection and cancellation of echo in a communications system is enhanced by taking advantage of the accumulated knowledge relating to the echo path delay that an adaptive filter acquires as a result of its adaptation process. Such knowledge improves significantly the ability of an associated Near-End-Speech (NES) detector to detect for the presence of near end speech.

Intelligent near-end speech detection

The detection of echo is enhanced using a coarse near-end speech detector at a Y-side of an echo canceler and using a more accurate near-end speech detector at the E-side of the echo canceler, such that the latter detector uses a representation of far-end speech and a threshold value to determine if the magnitude of the echo canceler output is larger than that of an echo signal only. If it is, and there is an absence of an indication of the presence of near-end speech from the coarse detector, then the more accurate speech detector adjusts the value of the threshold in a first direction, otherwise it adjusts the threshold in a second direction, to more 'finely tone' such accuracy.

Echo canceler E-side speech detector

Acoustic echos are canceled by employing a first echo canceler having a comparatively short first impulse response synthesis capability which is connected between a transmit path and receive path for generating a first error signal and for canceling echo signals in the transmit path, and at least a second echo canceler having a comparatively long second impulse response synthesis capability connected in parallel with the first echo canceler between the transmit and the receive path. The second echo canceler is supplied with the first error signal from the first echo canceler and is adaptively operating simultaneously with but independent of the first echo canceler to further cancel echos in the transmit path. More specifically, the first echo canceler is intended to capture the direct path acoustic echo and any early arriving echos that are stable which are not time yawing. Since the direct path acoustic echo and the stable early arriving echos are not time varying, the adaptive adaptation rate, i.e. loop gain, of the first echo canceler adaptation circuitry can be chosen to be a very small value so that it can adapt accurately in the presence of undetected near-end speech. Then, with the direct path acoustic echo and any stable early arriving echos having been substantially removed by the first echo canceler, the first error signal output from the first echo canceler has a comparatively weaker echo component to corrupt any near-end speech that might be present and, consequently, the near-end speech can be more reliably detected by monitoring the first error signal from the first echo canceler. Since the near-end speech can be more reliably detected by employing the first error signal from the first echo canceler, the adaptation rate of the second echo canceler can be chosen to be at a significantly faster rate without undo impairment caused by undetected near-end speech. In a specific embodiment of the invention, the first echo canceler employs a transversal filter having predetermined fixed coefficients in order to cancel the direct path acoustic echo component and any stable early arriving echos.

Acoustic echo canceler

Failure to cancel echos at frequencies in which the frequency characteristics of sub-band filters in the X and Y analysis filter banks overlag in subband echo cancelers is overcome by employing an X-analysis filter bank in which the pass-band of the subband filters is wider than the pass-band of the corresponding subband filters in the Y-analysis filter bank. This insures that there is sufficient energy in the tap delay lines of the adaptive filters in the subband echo cancelers at all frequencies where echos are to be synthesized. More specifically, the keeping of sufficient energy in the tap delay lines of the adaptive filters in the subband echo cancelers avoids exciting eigenmodes associated with the small eigenvalues of the correlation matrix.

Subband echo canceler

More efficent encoding/decoding in decomposing and recomposing a high resolution image is obtained by employing a unique pixel cluster arrangement. The pixel clusters of an image are classified as one of a plurality of classifications. A unique encoding/decoding technique is assigned to each classification. In one embodiment, a cluster including at least one high resolution pixel to be recomposed from a corresponding low resolution pixel which is a so-called exception to general prediction rules is classified as a first classification. A cluster including no pixels which are exceptions is classified as a second classification. Supplemental information is encoded/decoded for all pixels in a cluster classified as the first classification. Pixels in the cluster classified as the second classification are encoded/decoded according to the general prediction rules.

Efficient encoding/decoding in the decomposition and recomposition of a

In entropy, e.g. arithmetic, encoding and decoding, probability estimates are needed of symbols to be encoded and subsequently decoded. More accurate probability estimates are obtained by controllably adjusting the adaptation rate of an adaptive probability estimator. The adaptation rate is optimized by matching it to the actual probability values being estimated. In particular, the adaptation rate is optimized to be proportional to the inverse of the smallest value probability being estimated. Consequently, if the probability values being estimated are not small a 'fast' adaption rate is realized and if the probability values being estimated are small a necessarily slower adaptation rate is realized.

Adaptive probability estimator for entropy encoding/decoding

In entropy, e.g., arithmetic or adaptive Huffman, encoding/decoding a context based on prior symbols is needed to provide accurate predictions of symbols to be encoded/decoded. Encoding/decoding efficiency is improved by employing an adaptive context extractor. The adaptive context extractor automatically adjusts the configuration of the lag intervals used to define the context. This is realized by adaptively incorporating into the context configuration at least one lag interval found to have a 'good' predictive value relative to the particular symbol stream being encoded/decoded. The context configuration adjustment is such that the at least one found lag interval is exchanged with the lag interval currently in an at least one so-called floating predictor position.

Entropy encoder/decoder including a context extractor

More efficient encoding/decoding in decomposing and recomposing a high resolution image is obtained by employing a unique prediction arrangement. The prediction arrangement determines whether high resolution pixels to be recomposed from low resolution pixels from a low resolution replica of the high resolution are so-called typically predictable or non-typically predictable by using general prediction rules. The general prediction rules are also employed to determine if any of the typically predictable high resolution pixels would be improperly recomposed. Such high resolution pixels which would be improperly recompased are identified as exceptions. It is noted that so-called supplemental information is required to properly recompose non-typically predictable pixels and typically predictable pixels which are identified as exceptions. To this end, exceptions accompany the low resolution pixel for which the corresponding high resolution pixels would otherwise be improperly recomposed.

In order to employ an output register having a finite number of stages in an arithmetic encoder, it is necessary to provide carryover control, otherwise a register having an impractically large number of stages would be required, i.e., a so-called 'infinite' register. The so-called 'infinite' output register is emulated by employing a counter and a finite register. To this end, a count is accumulated of sets, i.e., bytes, of consecutive prescribed logical signals of a first kind, i.e., logical 1's, being generated by an arithmetic coding register and possibly modified by a carry indication. The accumulated count is then employed to supply as an output a like number of sets including logical signals of a second kind, i.e., logical 0's, or logical signals of the first kind, i.e., logical 1's, depending on whether or not a carry would propagate through the stages of the so-called 'infinite' register being emulated.

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Rumson, NJ, United States of America

Donald Lars Duttweiler