Abstract: A noise reduction filter (28) is provided. The noise reduction filter (28) comprises a signal analysis block (30). The signal analysis block (30) is operable to receive an input audio signal and to determine a short term signal level. A noise floor block (32) is coupled to the signal analysis block (30). The noise floor block (32) is operable to receive the short term signal level from the signal analysis block (30) and to determine a noise floor level based upon the value of the short term signal level. A noise factor block (34) is coupled to the signal analysis block (30) and to the noise floor block (32). The noise factor block (34) is operable to receive the short term signal level and the noise floor level and operable to calculate a noise factor. A multiplier node (36) is coupled to the noise factor block (34) and receives the input audio signal.

Abstract: An echo canceller (30) cancels an echo signal produced on a transmission path (14) on the basis of a received signal received through a reception path (15). The echo canceller comprises an adaptive filter (31) for producing a pseudo-echo signal from the received signal in accordance with tap gains. A producing section (19, 20) produces an error signal representative of an error level between the echo signal and the pseudo-echo signal. A supplying section (21, 32) supplies the adaptive filter with selected tap gains stored in a memory section (18) when the error level is less than a predetermined threshold level. The adaptive filter renews the selected tap gains into renewal tap gains in accordance with the received signal and the error signal to store the renewal tap gains of the selected tap gains in the memory section.

Abstract: The echo canceler includes an N-tap FIR filter and a coefficient controller. Previous filter coefficients which were generated before an estimation error occurrence when the transmitting output signal becomes greater in power than the transmitting input signal are obtained by using only a number S of coefficient correction values and another number (N-1+S) of sequentially received signals. Since the latest (N-1) received signals are stored in (N-1) delay circuits of an N-tap FIR filter, respectively, a relatively small capacity memory may be provided to store the earlier S received signals. The number S is determined so that a time interval determined by the number S of sampling instants is longer than a response time of a double talk detector.

Abstract: An architecture for echo cancellation in communication networks is provided that uses a multi-stage adaptation algorithm which operates on echo cancellation filters of different configurations. When each of the configurations exhibit increased sensitivity to a different adaptation parameters, the resulting architecture gains an increased estimation accuracy. The increased accuracy readily translates into improved echo cancellation performances. In one embodiment, the architecture includes a baseband filter configuration and a passband filter configuration for echo cancellation. The increased adaptation sensitivity of the baseband filter configuration allows a more accurate estimate of the frequency offset. This estimate may then used by the passband filter configuration to attain a better echo cancellation performance.

Abstract: 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.

Abstract: A telecommunication signal processor includes a noise compensation system for preventing undesirable spectral modulation of the noise component of a telecommunication signal subjected to a process wherein subband portions of the signal are variably attenuated. A noise component is injected into each attenuated error signal in order to compensate for attenuation of background noise incidental to the variable attenuation of the subband signals. The amplitude of the noise components are each determined independently on the basis of an estimated noise content of the original subband signals and in accordance with the applied attenuation within each subband. The attenuated and noise-compensated subband signals are combined by a synthesis filter to provide a send-output signal.

Abstract: A method for controlling echo canceling in an echo cancellation system using a state machine controller. A far-end speech signal transmitted through a communications channel may be passed through an echo channel to produce an echo signal. The echo signal is summed with a near-end speech signal and transmitted back to the far-end. An echo canceller rejects the echo signal by forming an estimate of the echo signal and subtracting the estimate from the sum of the near-end speech signal and the echo signal. The echo canceller includes a state machine which is configured into a predetermined state of a plurality of states depending on the presence near-end speech signal, far-end speech signal, or both near-end and far-end speech signals. Based on the predetermined state of the state machine, the controller in the state machine controls the update of coefficients of a plurality of adaptive filters.

Abstract: To improve the signal to noise ratio of the receiver of a transmitting modem, the transmitting modem is equipped with the ability to cancel the far listener echo. Advantageously, doing so allows higher data rates or reduced error rates. Cancellation of the far listener echo is achieved by coupling the signal containing the in-phase, quadrature (also known as X and Y, or real and imaginary) components of the modem transmit signal to a far echo canceller that is included in the modem in addition to the far echo canceller conventionally found in modems. However, the bulk delay employed by the additional far echo canceller is arranged to be a delay of two round trips between the transmitting modem and the receiving modem rather than the conventional single round trip delay of the conventional far echo canceller.

Abstract: To improve the signal to noise ratio of the receiver of a receiving modem, the receiving modem is equipped with the ability to cancel the listener echo. Cancellation of the listener echo is achieved by coupling to the listener echo canceller of the receiving modem the phase corrected adaptive equalizer output signal, which is conventionally found in modems. The phase corrected adaptive equalizer output signal contains the in-phase, quadrature (also known as X and Y, or real and imaginary, components of the) received modem signal at the symbol rate. Advantageously, doing so results in an improved SNR for the receiver of the receiving modem, thus allowing higher data rates or reduced error rates without requiring extension of the length of the modem equalizer. When the telephone network does not introduce any frequency offset of the modem signal in the channel, the listener echo canceller may be simplified to reduce its cost.

Abstract: 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.

Abstract: An adaptive signal processing device employed in a hand-portable telephone configured to adaptively estimate signal transfer characteristics in a transmission system and process signals based upon such estimation includes a power calculating unit, a filter coefficient updating unit, an arithmetic-logical unit and an echo removing unit. The power calculating unit calculates the power of a first input signal x(n) entering the device via a transmission system. The filter coefficient updating unit calculates a filter coefficient h(n+1)(i) updated at time n+1 based upon the first input signal x(n), a signal e(n) corresponding to a second input signal d(n) to be transmitted over the transmission system less a pseudo-echo component, a signal 2.sup.Pe outputted by the power calculating unit, a control constant a and a filter coefficient h(n)(i) at time n, in accordance with an equationh.sub.(n+1) (i)=h.sub.(n) (i)+.alpha.(e(n).times.(n-i))2.sup.

Abstract: An echo canceller is disclosed which generates an echo replica based on a transmit signal to cancel an echo. The echo canceller includes a linear echo canceller circuit for generating an echo replica of the transmit signal in the absence of distortion. The echo canceller further includes a waveform-distortion compensation circuit, coupled with the linear echo canceller circuit, for generating an echo replica for compensating waveform distortion occurred in an echo response when the transmit signal is distorted. In the echo canceller, the echo is canceled by use of the echo replica generated in the linear echo canceller circuit in the absence of distortion in the transmit signal, and is canceled by use of the echo replica generated in the waveform-distortion compensation circuit when the transmit signal is distorted.

Abstract: A echo-canceling modem uses pre-emphasis in both the transmitter and receiver sections. In particular, the receiver section of the modem processes a received signal with a pre-emphasis filter before performing echo cancellation on the received signal. The receiver pre-emphasis filter is identical to the transmitter pre-emphasis filter, i.e., the pre-emphasis added in the receiver is the same as the pre-emphasis added in the transmitter.

Abstract: A method and apparatus for performing subband adaptive filtering is proposed. A signal is prefiltered by a set of complementary filters to provide corresponding subbands of the input signal. The subbands of the signal are then provided to adaptive filters that filter the subbands separately. The individually filtered subbands are then summed. In an exemplary implementation an echo canceller is presented which employs the subband filtering method and apparatus.

Abstract: An adaptive filter in the form of an FIR or IIR filter performs an adaptive filtering process relative to an input signal using a plurality of tap coefficients. The adaptive filter derives a vector formed by absolute values of the plurality of tap coefficients and weights step sizes of the plurality of tap coefficients using the first vector. The adaptive filter updates the plurality of tap coefficients based on the weighted step sizes. With this arrangement, the optimum tap coefficients can be achieved with high convergence speed. The adaptive filter is applicable to an echo canceller, such as, an acoustic echo canceller or a line echo canceller, so that echo canceling is effectively achieved by updating the tap coefficients with high accuracy and with high speed.

Abstract: Echo canceler. A circuit arrangement for the cancellation of echo signals, wherein in the received path, an analog/digital converter is connected with a first adder and a second adder is interposed after the analog/digital converter, with the estimated echo signal being divided into first and second portions, whereby the first portion is transmitted to the first adder and the second portion is transmitted to the second adder for the production of the received signal. In a further embodiment, a third adder is interposed between the analog/digital converter and the second adder, via which the output signal of a compensation filter is added to the signal in the received path.

Abstract: A double-talk detector for an echo canceller includes power estimators (60) and (62) which are utilized to measure the ERLE value in a calculator (64). This ERLE value is stored in a register (70) when it is the largest value generated. This register (70) is updated whenever a new and better ERLE occurs. A fraction of the value in register (70) is utilized as an input to a comparator (88), and then compared to the current ERLE value. If the current ERLE differs from the SERLE in register (70) an inhibit signal is generated for blocking the updates of an adaptive filter (40). The value stored in the register (70) is periodically decremented to reduce the value thereof. This decrement operation is performed in response to detection of an utterance from the far-end.

Abstract: An echo canceller for use in fixed-wireless telephony networks using low-rate packetized speech coding and DSI is disclosed. An adaptive filter is used to cancel an echo signal of a far-end signal introduced at the near-end by operating to provide a replica signal to cancel the echo signal. The replica signal is updated in the absence of a near-end talker signal presence of near talker signal is detected using an estimated echo-residual loss. The echo replica signal updating process is frozen upon the detection of double-talk. Residual echoes are suppressed without the use of non-linear processing. A residual suppression flag detection and a voice activated switching device are used to detect the absence of near-end signals. The switching device is opened if the signal to be transmitted is not a near-end signal or is noise.

Abstract: A signal processor for, e.g., a telephonic communication system interconnecting a near location and at least one far location includes an echo canceller for suppressing the re-transmission of received signals. The operation of the echo canceller is controlled according to whether the near location is transmitting or receiving, and whether the far location is transmitting or receiving. The signal processor includes means for detecting doubletalk, and for controlling the echo canceller in response to the detection of doubletalk, such that doubletalk is permitted. In one method of operation, a delay is applied to the inputs to the echo canceller from the near and far ends, such that each of these signals is used for determining the operating state of the echo canceller before being used to operate an adaptive filter of the echo canceller. In another method of operation, doubletalk detection is carried out, in part, by evaluating the performance of an auxiliary adaptive filter.

Abstract: A finite impulse response (FIR) filter characterization is performed using a modified least means squares approach that updates values of FIR filter taps as groups of taps, periodically. For the taps updated for a current input signal sample, future convolution values for future input signal samples are computed and also a partial estimate of the signal response is computed. The expected response is then computed by summing the partial estimate signal response and other partial estimates of the signal response which are computed from future convolution, missed tap update convolution and normalizes error signal values which have been previously computed at past input signal samples and stored in memory.