Abstract: A system for updating filter coefficients for use with an echo canceller, a related method for updating filter coefficients and an echo canceller including the system or the method. In one embodiment, the echo canceller has a nonadaptive filter and an adaptive filter, the nonadaptive filter having nonadaptive filter coefficients and configured to develop a nonadaptive error signal as a function of the nonadaptive filter coefficients, and the adaptive filter having adaptive filter coefficients and configured to develop an adaptive error signal as a function of the adaptive filter coefficients. The system includes a monitoring subsystem configured to monitor a quality of the nonadaptive and adaptive error signals and a selection subsystem configured to select one of the nonadaptive and adaptive filter coefficients for use by the nonadaptive filter based on the quality of the nonadaptive and adaptive error signals.

Abstract: An echo canceller circuit for use in an echo canceller system is set forth that provides sensitive non-linear echo path response detection. The echo canceller circuit comprises a first digital filter having non-adaptive tap coefficients to simulate an echo response occurring during a call. A second digital filter having adaptive tap coefficients to simulate an echo response occurring during the call is also used. The adaptive tap coefficients of the second digital filter are updated over the duration of the call. A coefficient transfer controller is disposed in the echo canceller circuit to transfer the adaptive tap coefficients of the second digital filter to replace the tap coefficients of the first digital filter when a set of one or more transfer conditions is met. A non-linear echo path response detector is provided. The non-linear echo path detector is responsive to one or more parameters of the first and second digital filters to detect a non-linear echo path condition.

Abstract: An adaptive filter is programmed with an algorithm based on a normalized Least Mean Squares (nLMS) algorithm that adapts each sample time. The algorithm is modified to be more efficient in a variety of DSPs by computing multiple errors, one per sample, before updating coefficients. The update equation utilizes the multiple errors to achieve adaptation at a similar performance to known nLMS algorithms that adapt each sample time but without the instability that is observed in low echo-to-near-end-noise ratio (ENR) input conditions. Varying the relaxation step size prevents divergence. The DSP utilizes either one or more MAC units.

Abstract: A combined processor, such as might be used in a mobile handset or hands-free communication device, provides residual echo suppression and noise reduction while eliminating the need for explicit comfort noise generation. Operating within a near-end communication device, the processor receives an echo-canceled signal that is derived from a near-end input signal, and generates an output signal for subsequent transmission to a far-end communication device by applying a noise attenuation factor to the echo-canceled signal or to an average of that signal. The processor maintains the average signal across periods of speech and non-speech. During far-end-modes of operation, where only incoming audio from the far-end is active, the processor substitutes the average signal for the echo-canceled signal, such that a far-end listener receives the natural sounding average signal without receiving the objectionable, residual echo that may be in the echo-canceled signal.

Abstract: A terminal in a communication system includes emitting and receiving transducers and an echo processor having an adaptive echo canceler that processes a residual echo output from the adaptive echo canceler.

Abstract: A non-linear processor for use in an echo canceller is set forth. The non-linear processor includes a center clipping digital filter receiving an echo compensated signal. The non-linear processor provides a center clipped output signal having non-linear thresholds at values of +TNLP and ?TNLP. The value of TNLP is dynamically dependent, at least in part, on echo return loss measurements. To limit the processor's susceptibility to corruption from double-talk conditions, the non-linear processor inhibits the dynamic setting of the TNLP value when a double-talk condition is present. Additionally, or in the alternative, the non-linear processor locks the value of the echo return loss measurement after a predetermined number of consecutive echo return loss measurements have values falling within a predetermined range of one another. Such locking further reduces the susceptibility of the non-linear processor to corruption from double-talk conditions.

Abstract: Methods and apparatus for processing a received voice signal from a variable-delay network by a communications system that has at least one echo canceller. An echo canceller determines delay characteristics that are associated with the received voice signal and correspondingly modifies echo cancellation processing. In a variation of the embodiment of the invention, a first echo canceller sends silence descriptor information to a second echo canceller. The second echo canceller reconstructs a voice signal based upon the silence descriptor information and excitation vector information.

Abstract: The present invention provides an acoustic echo canceler for use in a telephone set having a handsfree conversation function. This acoustic echo canceler simultaneously achieves both the stabilization and speedup of an estimation operation and also attains the more improvement of speech quality. Moreover, the present invention provides a handsfree telephone set employing this acoustic echo canceler. Furthermore, this acoustic echo canceler is operative to cancel an echo generated by inputting an output of an acoustic device to itself substantially simultaneously with the outputting the output thereof. Further, this acoustic echo canceler comprises an adaptive filter for performing an operation of estimating the frequency characteristic and the phase characteristic of a part, whose frequency characteristic and phase characteristic vary, on an acoustic path and a fixed coefficient filter for simulating a part, whose frequency characteristic and phase characteristic are fixed, on the acoustic path.

Abstract: Techniques for canceling echo and suppressing noise using an array microphone and signal processing. In one system, at least two microphones form an array microphone and provide at least two microphone input signals. Each input signal may be processed by an echo canceller unit to provide a corresponding intermediate signal having some echo removed. An echo cancellation control unit receives the intermediate signals and derives a first gain used for echo cancellation. A noise suppression control unit provides at least one control signal used for noise suppression based on background noise detected in the intermediate signals. An echo cancellation and noise suppression unit derives a second gain based on the control signal(s), cancels echo in a designated intermediate signal based on the first gain, and suppresses noise in this intermediate signal based on the second gain. The signal processing may be performed in the frequency domain.

Abstract: A method for suppressing echo signals generated in a communication path such as acoustic coupling between a speaker and a microphone in a telephone device handset includes the steps of monitoring signals supplied to the communication path to determine an attribute thereof and masking signals received from the communication path as a function of the determined attribute of the monitored signals thereby to suppress echo.

Abstract: A method is provided for detecting echo cancellation in a communication network. The method includes the steps of transmitting from an originating unit a pre-defined echo cancellation detection signal to a receiving unit. The resulting signal is detected by the receiving unit and analyzed to determine whether the differences between the resulting signal and a stored pre-defined signal indicate the detection of echo cancellation on the communication network.

Abstract: Device and method for noise suppression in telephone equipment, in particular with hands-free equipment, having a level discriminator, an additional filter with a group propagation time of less than 2 ms being inserted into the transmission and receiving paths of the telephone equipment.

Abstract: A gain control method for reducing or eliminating the undesirable effects of acoustic echo coupling between a speaker and a microphone while providing a full-duplex connection. Weighted normalized far-end and near-end powers are used to first calculate a suppression value which is used to determine the attenuation factor between an upper and a lower limit, thus improving reliability in noisy environments. To further improve the quality of the full-duplex connection, a smoothing factor is applied to the attenuation calculation to provide a low power and constant sounding echo without annoying transient-like sounds.

Abstract: A communication system having an echo canceller is disclosed. One embodiment of the echo canceller includes an adaptive filter used to provide an estimate of reflected echo which is removed from the send signal. The echo canceller may also include a near-end talker signal detector which may be used to prevent the adaptive filter from adapting when a near-end talker signal is present. The echo canceller may also include a nonlinear processor used to further reduce any residual echo and to preserve background noise. The echo canceller may also include a monitor and control unit which may be used to monitor the filter coefficients and gain of the adaptive filter to maintain stability of the echo canceller, estimate pure delay, detect a tone, and inject a training signal. The echo canceller may also include a nonadaptive filter used to reduce the length of the adaptive filter.

Abstract: Echo return loss is analyzed to determine if the near end connection of a communication link has hybrid induced echo. If the echo return loss is above a threshold value for a predetermined period, than no echo or very little echo is present. The lack of echo is treated as a four wire connection and the near end signal is processed accordingly. If the foreground and background filter update relationship indicates the presence of a hybrid or if the echo return loss drops below a second threshold, the condition of the near end signal is treated as a two wire hybrid induced echo. The analysis of the near end signal continues and treatment of the signal may switch between four wire and two wire any number of times during a communication link.

Abstract: An echo cancellation system for detecting and canceling echo from a network speech path, comprising a pool of echo locators for detecting pure echo delay and dispersion of time, a pool of echo cancellers, a pool of line watchdogs for detecting presence or absence of echo in the network speech path, and a control system for (i) locating and applying an echo locator from the pool of echo locators to the network speech path for detecting the pure echo delay and dispersion of time of any echo in the network speech path, and thereafter returning the echo locator to the pool of echo locators; (ii) locating and applying an echo canceller from the pool of echo cancellers to the network speech path for canceling the echo using the pure delay and dispersion time, and thereafter returning the echo canceller to the pool of echo cancellers; and (iii) locating and applying a line watchdog from the pool of line watchdogs to the network speech path for detecting said presence or absence of echo, and in the event the presence

Abstract: A method of estimating an echo return loss of a communication link measures the peak power value of a signal received from a far end of a communication link and the corresponding peak power value of a signal received from the near end of the communication link. When the near end signal is free from near end voice and excessive noise, the near end corresponding peak will be the echo of the far end power. The far end power is monitored and when a peak is detected, a period, which can be equal to a filter length period, is initiated. When the period has run, the delay line attached to the near end is polled to determine the peak power in the delay line. This peak power will correspond to the far end peak. If a peak, exceeding the first peak is detected before the period has run, the period is reinitiated. The echo return loss estimate is calculated as a ratio of the far-end peak power value to the near-end peak power value.

Abstract: A method includes receiving a plurality of packets from at least two voice packet streams. The method also includes generating at least two voice signals using the plurality of packets. Each voice signal is associated with one of the voice packet streams. In addition, the method includes identifying an echo of one of the voice signals in at least one other of the voice signals.

Abstract: A communication system being made up of a two-wire/four-wire hybrid circuit, an echo canceller, and a control device and having functions of forming a plurality of communication paths and changing communication paths is provided which is capable of ensuring high speech quality by suppressing and canceling an echo occurring in telephone speech after establishment of path connection. The communication system also includes a training signal source to feed a training signal to the echo canceller, a switching circuit to do switching of a signal to be fed to the echo canceller between an ordinary signal and the training signal, and a control device to exert control on path connection and path changing and to feed the training signal to the switching circuit to make a training signal be fed from the training signal source to the echo canceller and to have the echo canceller converge its training operation.

Abstract: The invention is an echo canceller for reducing the magnitude of an echo occurring in a return channel of a communication device and a method of implementing the same. The echo canceller includes a processing unit for generating an echo attenuated signal. The processing unit includes a first input, a second input and an output. The first input is for receiving a first signal that is the precursor of the echo. The second input is for receiving a second signal that potentially contains the echo. The output is for outputting the echo attenuated signal. The echo attenuated signal is derived by combining the second signal and an adaptation signal. The adaptation signal is generated by normalizing the echo attenuated signal to produce a normalized adaptation signal, and combining the normalized adaptation signal with the first signal to generate an intermediate signal. Additionally, the intermediate signal is de-normalized to produce the adaptation signal.

Abstract: An echo canceller includes two parallel filters and a controller. The controller chooses the best of the two filters for the final echo cancellation. The filter coefficients are exchanged between the two filters constantly so that both filters retain performance all the time even if double-talk and echo path variations occur very closely in time. One filter is strongly robust and will not diverge during double-talk, and another filter is weakly robust and will converge rapidly during echo path variation.

Abstract: An echo cancelling system for cancelling echoes in a communication path includes an echo locator and an echo canceller. The echo locator is coupled to the communication path and locates the positions of echo signals received from the communication path. The echo canceller is also coupled to the communication path and cancels echo signals received therefrom. During echo cancellation, the echo canceller becomes active in regions corresponding to the positions of echo signals in response to the echo locator.

Abstract: The invention provides an apparatus and method for bulk delay insertion prior to echo cancellation, with echo suppression. The exemplary apparatus embodiment (100) bandpass filters (120) and down samples (130), by a down sampling factor, a reference signal and a combined signal that includes an echo of the reference signal. An adaptive echo delay filter (140) determines a plurality of filter coefficients, using the down sampled reference signal, and using an error signal formed as a difference between the down sampled combined signal and the adaptive echo delay filter output. When the filter coefficients have converged, an echo delay time period is determined as a product of the tap location of the maximum filter coefficient and the down sampling factor. When the echo delay time period is greater than the capacity of an associated echo canceller, an adaptive delay inserter (110) inserts the echo delay time period prior to echo cancellation.

Abstract: A process is described which generates matrix coefficients using zero-lag auto and cross-correlations from signals commonly found in echo cancellers. Double-talk and path changes are then detected using matrix operations such as determinants, eigendecompositions, or singular value decompositions (SVDs). In a preferred embodiment, the determinant of the correlation-based matrix is compared against predetermined threshold values.

Abstract: An echo canceler for generating an echo replica and subtracting the echo replica from a local input signal to create a residual signal for outgoing transmission. An echo canceler has adaptive filters that have different computational accuracy generating the echo replica. An evaluator coupled to the adaptive filters groups coefficients into each of segments, and evaluating a computational accuracy information according to the coefficients for the segments. A computational accuracy controller in the evaluator assigns the local input signal to the adaptive filters, and adjusts the coefficients according to the computational accuracy information.

Abstract: A communication transmitting and receiving system in which the effects of near-end echo and near-end crosstalk signal from the communication medium are mitigated by adaptively reproducing the near-end echo and near-end crosstalk signal, which is then subtracted from the received signal. Filter coefficients for a Finite Impulse Response filter are adaptively generated to reproduce the near-end echo and near-end crosstalk. The filter coefficients are regenerated for the Finite Impulse Response filter in an adaptive correlator at the arrival of each received signal and whereby each new filter coefficient is a weighted sum of a previous coefficient and one received signal multiplied by a time delayed version of one transmitted signal.

Abstract: An echo canceller used in a vocal information exchange system operates in such a circumstance that a sound wave released by a speaker is picked up by a microphone unintentionally and works to suppress an echo signal included in the audio signal produced by the microphone by using a pseudo echo signal which is produced based on the incoming audio signal to be fed to the speaker and produce a subtracted audio signal which becomes the outgoing audio signal, with the echo signal being suppressed based on the accurately-calculated degree of echo suppression achieved by use of the pseudo echo signal.

Abstract: System and method for processing communication signals in a communication system having a detector for detecting a parameter of a communication signal. A communication signal is provided to a non-linear processor (NLP) adapted to examine the signal and to decide whether or not to enter an active state based upon a parameter of the signal. If the NLP enters an active state, the NLP performs non-linear processing on the signal. The NLP communicates to the detector whether the NLP is active or inactive. If the NLP is active, a processing step of the detector is disabled.

Abstract: This invention discloses an improvement to a digital Acoustic Echo Control (AEC) in hands-free telephones. It describes an additional adaptive filter referred to as a residual echo filter, which is placed after the usual echo canceller and it is used to efficiently and accurately estimate a residual echo signal b(i) and a system coupling factor ?(i), which can be utilized to establish an efficient control for the AEC system and construct the appropriate filters. The invention also describes a control block means performing a joint operation control of the echo canceller, residual echo suppressor and residual echo filter for achieving more consistent echo cancellation results and enhancing output signal quality.

Abstract: A network gateway is configured to facilitate on line and off line bi-directional communication between a number of near end data and telephony devices with far end data termination devices via a hybrid fiber coaxial network and a cable modem termination system. The described network gateway combines a QAM receiver, a transmitter, a DOCSIS MAC, a CPU, a voice and audio processor, an Ethernet MAC, and a USB controller to provide high performance and robust operation. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or the meaning of the claims.

Abstract: Long distance telephone connections must commonly employ echo cancellers to eliminate irritating echo. The normal practice is to additionally employ non-linear processors (NLPs) as an integral component of an echo canceller in order to eliminate small residual echo which remains after initial echo cancellation. While such devices do indeed remove remaining residual echo, they also may introduce additional problems, such as suppression of the background signal. However, in some cases there is no need to deploy a potentially problematic non-linear processor. If the overall route delay of the telephone connection is not excessive, the participants do not notice the residual echo. Therefore, a determination is made of the end to end delay of the overall telephone connection. If the determined delay is not excessive, non-linear processing is not applied or is applied less aggressively. This results in a clearer telephone call, free from non-linear processor problems.

Abstract: An adaptive digital filter (10) is adapted to generate a pseudo echo Se which is produced by imitating a noise, using part of receiving signals Si and to output it. An echo produced through an echo path (15) is mixed, as an echo noise, with a sending signal So and this sending signal is attenuated by a level attenuator (6). The level attenuator (6), in order to match the amplitude level of the echo noise of the sending signal So to that of the pseudo echo, attenuates the sending signal So and feeds it to a subtracter (7). The subtracter (7) eliminates echo noises by subtracting the pseudo echo Se from the sending signal So. Even if the echo path is in the state of amplified system, the complete elimination of the echo can be achieved accordingly.

Abstract: A separation circuit, method of determining a residual level of an echo, and an echo canceling system, bit pump and transceiver employing the circuit and method. The echo canceling system employing the separation circuit is couplable between a transmit and receive path of the bit pump and generates an echo canceling signal. In one embodiment, the separation circuit includes a symbol determination circuit that accepts a receive signal, propagating along the receive path, substantially free of an echo and determines a symbol associated with the receive signal. The separation circuit also includes an estimator stage, coupled to the symbol determination circuit, that receives the symbol and provides an estimated receive signal. The separation circuit generates data representing a residual level of the echo as a function of the estimated receive signal and the echo canceling signal.

Abstract: A digitized input signal is sampled, to obtain a reference input signal. The reference input signal is spuriously whitened, to obtain a pseudo whitened signal. An echo replica signal is generated on the basis of the pseudo whitened signal and an adaptive filter coefficient. A cancellation error signal is obtained on the basis of an echo signal and the echo replica signal. The adaptive filter coefficient is updated on the basis of the cancellation error signal, the adaptive filter coefficient, and the pseudo whitened signal.

Abstract: Real and imaginary components of the discrete Fourier transform (DFT) of the residual echo in an acoustic echo cancellation system are separately estimated using mapping functions derived without an assumption of statistical independence between separate components of a near-end microphone input signal. The residual echo estimator calculates the real and imaginary components using an approximation of the microphone input signal without the echo. A different approximation is used depending on whether the near-end talker and/or the far-end talker are talking.

Abstract: Method and device for echo compensation with a common-frequency transmission method in duplex mode over a two-wire line, an echo compensation filter which has adjustable coefficients and is embodied as an FIR filter being arranged between the transmitter output and receiver input and an IIR filter with adjustable coefficients, whose coefficients can be determined as a function of the coefficients of the FIR filter, being additionally provided.

Abstract: An echo cancellor having a main tap coefficient holding section to renew a tap coefficient used to establish a pseudo transmission characteristic of an echo path and a sub tap coefficient holding section to make a copy of a tap coefficient held by the main tap coefficient holding section and to hold it. The copying is made each time an echo suppressing rate is increased. Accordingly, a tap coefficient having a high echo suppressing rate is held by the sub tap coefficient holding section. In this state, if an ambient noise such as an alarm of whistle of a vehicle is mixed, renewal operation of the main tap coefficient holding section is halted and a tap coefficient held by the sub tap coefficient holding section is used. Even in the case of a divergence of the main tap coefficient, normal operation can be maintained by the tap coefficient held by the sub tap coefficient holding section accordingly.

Abstract: A method and apparatus is capable of detecting the presence of a non-linear echo path as well as transitions from non-linear echo path to linear echo path and vice versa. Additionally, when non-linear echo path is detected, the echo canceller (12) is configured to follow a prescribed logic routine that combats possible echo leak-through as a result of compromised cancellation due to non-linearity. This prescribed logic routine affords the echo canceller (12) protection against non-linear echo path by preserving an already converged state of the echo canceller (12) from possible divergence due to the occurrence of non-linearity in the echo path and thereby prevents echo leak-through that would occur due to divergence of the echo canceller (12).

Abstract: A filter cell, method of deriving an echo component and an echo canceling system, bit pump and transceiver employing the same. In one embodiment, the filter cell includes a first summing node that receives a first input based on a signal sample that contains an echo component of an echo. The filter cell also includes a second summing node that receives a second input based on the signal sample. The filter cell still further includes a multiplier that employs outputs from the first and second summing nodes and a scaling factor to derive first and second outputs containing a remnant of the echo component.

Abstract: A base band echo cancellation method and apparatus utilizing Laguerre echo estimation. The method begins with a series of transmitted symbols that are stored in a buffer. The buffer is segmented into a head portion and a tail portion. The symbols in the tail portion are passed through a Laguerre or IIR filter and then reinserted into the tail portion of the buffer. An echo estimation signal is generated based on the symbols in the buffer. The apparatus includes a transmit symbol buffer that is coupled through a modulator to a Laguerre or IIR filter. A demodulator couples the filter back to the buffer. An echo estimator is also coupled to the buffer.

Abstract: A method and an apparatus for echo cancellation in a digital data transmission system in which system the end of a transmission link to which sound returns as an echo is the far end and the end of the transmission link from which an echo is reflected back is the near end, and in which a speech coding method is used on the echo path at least for a far-end signal transmitted from the far end to the near end, the method comprising the following steps: the echo originating from the near end is estimated with an adaptive linear filter on the basis of the far-end signal, and the echo estimate is subtracted from the near-end signal transmitted from the near end to the far end, whereby the speech-encoded far-end signal is decoded in an echo canceller, and the echo originating from the near end is estimated on the basis of said decoded far-end signal.

Abstract: In a line driver/receiver circuit where the line driver is connected with its output terminals to a load for supplying a transmit signal thereto and where the receiver is connected with its input terminals to the load for simultaneously receiving a receive signal therefrom, the transmit signal on the input terminals of the receiver is canceled by connecting the output terminals of the line driver to the load via equal complex sense impedances of an impedance value that is much smaller than the impedance value of the load impedance to match the load impedance, connecting the input terminals of the receiver to the load via equal first resistors and to respective output terminal of the line driver via equal second resistors, and providing transconductance amplifiers to sense the voltage across the sense impedances and supply corresponding currents to respective input terminal of the line driver.

Abstract: A technique for echo cancellation that suppresses echo leak through includes generating a synthetic echo signal and a center clipper signal from a reference signal, generating an error signal from a desired signal that has been added to a negative of a synthetically generated echo signal; and generating an improved center clipper signal from the center clipper signal, the reference signal, the error signal, and the echo cancelled signal.

Abstract: 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).

Abstract: An apparatus of a digital echo canceller and method therefor, a designed selector is used values of receiving and input signals to estimate the length of a cable. The response values of an insignificant part of the echo signal can be selected. Multiplication and addition operations are carried out in a response region of a significant part of the echo signal. An estimated echo signal is produced to cancel the echo signal, unnecessary operations and the cost of a hardware can be reduced.

Abstract: An echo canceller and a method of echo cancellation using an NLMS algorithm. The NLMS algorithm alternates adaptation between a slow mode, aggressive mode, and inhibition mode, according to the status of the echo canceller. This implementation requires no correlation information. This implementation is simple and not very time consuming. During initial conversation, the NLMS algorithm is in an aggressive mode to ensure fast convergence. After convergence, the NLMS algorithm switches to a slow mode for lower residual echo return. Whenever an abrupt increase of residual echo caused by either double talk or echo path change is detected, the current adaptive filter coefficients are retained and then updated in the aggressive mode. The decision as to which echo estimation (the response of the retained filter or the response of the aggressively adapted filter) is subtracted from the reference echo for echo cancellation within a short detection delay period is determined according to the Geigel algorithm.

Abstract: The present invention is a method and apparatus for estimating the bulk delay and span associated with an echo signal on a telephone line carrying a proximal signal and an echo signal. A baseline solution is to use the echo canceller itself to estimate the bulk-delay. After achieving a reasonable level of echo cancellation, the bulk-delay and the echo-span are estimated from the adaptive coefficients, followed by an enhanced mode of operation using the estimated parameters. Alternatively, for longer, unknown bulk delays, a subband adaptive system is used to estimate the bulk-delay and echo-span. The subband adaptive echo canceller outputs the set of subband adaptive coefficients to a full-band echo canceller after achieving a reasonable level of convergence.

Abstract: A method and apparatus for performing double-talk detection in an acoustic echo canceller in which a detection statistic is advantageously computed based on an estimate of a cross-correlation between the far-end signal and the return signal which has been normalized with use of an estimate of a covariance matrix of the far-end signal. The estimate of the cross-correlation between the far-end signal and the return signal may be further normalized with use of either an estimate of a variance of the return signal or an estimate of a covariance matrix of the return signal. In certain illustrative embodiments of the invention, one or more of these quantities may be estimated based on signal samples sampled over a predetermined time window. And in another illustrative embodiment of the present invention, the coefficients of the adaptive filter employed in the acoustic echo canceller itself are advantageously used to compute the detection statistic.

Abstract: A system for creating a comfort noise signal, said system includes a clipping circuit, a comfort noise generator, and a switch. The clipping circuit receives a near-end signal, a far-end signal and a residual signal. The clipping circuit determines the power of the far-end signal, the power of the near-end signal and the power of the residual signal. The clipping circuit determines the ratio of the power of the near-end signal to the residual signal and whether the ratio is less than a predetermined threshold. A comfort noise determination block is coupled to the residual signal and selectively forms a comfort noise signal. A switch is coupled to the comfort noise determination block and the clipping circuit. The switch is activated to transmit the comfort noise signal whenever the ratio of the power of the near-end signal to the residual signal is less than a predetermined threshold.

Abstract: An echo canceling apparatus includes a long-response echo canceler that removes an echo of an incoming signal from an outgoing signal by operating on a most recent segment of the incoming signal, stored in a tapped delay unit. The apparatus has a control unit that calculates a cancellation characteristic for each tap of the tapped delay unit. The cancellation characteristics are used to select a subset of taps corresponding to a changing component of the echo, the subset being empty if there is no changing component. A short-response echo canceler, operating on the outputs of the selected taps, cancels the changing component of the echo left uncanceled by the long-response echo canceler. Alternatively, the step gain of the selected taps is increased. The short-response echo canceler is preferably disabled in the double-talk state.