Abstract: To provide a noise suppressing device which accurately suppresses weak electric field strength pulse noise. A band-limiting unit (5) band-limits a composite signal obtained by demodulating an FM baseband signal, to a frequency band equal to or lower than a predetermined frequency so as to output a monaural audio signal. A pulse detecting unit (62) which detects pulse noise in the audio signal outputted by the band-limiting unit (5). A pulse judging unit (63) judges that a detection result of the pulse detecting unit (62) is valid in the case where pulse noise is detected in the composite signal, at a position corresponding to the detected pulse noise. A pulse suppressing unit (64) suppresses the pulse noise detected in the audio signal, in the case where the pulse judging unit (63) judges that the detection result is valid.

Abstract: The present invention relates to a method for attenuating near-end crosstalk between a remote received signal and a locally transmitted signal in a bidirectional signal transmission wherein said method comprises the step of producing an analog automatic feedback-driven correction loop in order to provide a no-correlation between said transmitted and received signals and to a hybrid circuit for enabling said method.

Abstract: A determination to enable echo cancellation is made in advance of a real-time communication session. A model sample audio file stored in memory on the computer system is played through a loudspeaker connected with the computer system. The sound generated by the loudspeaker is captured by a microphone connected with the computer system to create a captured audio signal. The captured audio signal is correlated with the sample audio signal to determine the presence of any echo effect in the captured audio signal. Characteristics of any echo in the captured audio signal, for example, frequency, delay, and gain, are parameterized and stored as initial values for use by the echo cancellation algorithm. The stored parameters are used by the echo cancellation algorithm at the initiation of a communication session until the algorithm receives enough real-time information to make any necessary ongoing adjustments.

Abstract: A method and apparatus to perform buffer management for media processing are described.

Abstract: A method and system in network switch for cancelling multiple sources of network echo, including echo that is combined with a persistent, non-echo signal. A first echo canceller cancels a first echo signal that arises from an echo path in the network switch, and second echo canceller cancels a second echo signal that arises from an echo path in an external network device. The first echo canceller operates by first removing any persistent, non-echo signal that may be combined with the first echo signal, then training on the remaining, pure echo signal. The second echo canceller includes two sub-component echo cancellers that are coordinated so as to provide a minimum error signal for cancellation applied to the second echo signal.

Abstract: A communication circuit includes a near end transmitter, a hybrid having an input in communication with an output of the near end transmitter, and a near end adjustable load replication transmitter having an adjustable load. The communication circuit further includes a subtractor configured to subtract an output from the near end adjustable load replication transmitter from the output from the near end transmitter and the hybrid. The communication circuit further includes a near end receiver responsive to an output of the subtractor and a calibration circuit configured to adjust the adjustable load against a reference load.

Abstract: A communication circuit comprises a near end transmitter, and adjustable near end replication transmitter and a near end receiver. The near end transmitter is configured to generate a transmission signal and comprises a first plurality of current sources. Outputs of the first plurality of current sources are summed to generate the transmission signal. The adjustable near end replication transmitter comprises a second plurality of current sources. Outputs of the second plurality of current sources are summed to generate a replication signal in accordance with the transmission signal. The replication signal from the adjustable near end replication transmitter is subtracted from the transmission signal from the near end transmitter and a received signal from a communication channel to generate a subtraction signal. The near end receiver is configured to receive the subtraction signal.

Abstract: A mobile communication terminal equipped with speaker phone functionality and a method for removing feedback when the speaker phone is in use are disclosed. The mobile communication terminal includes: a first voice input path serving as a default voice input path; a second voice input path serving as an additional voice input path; and a controller for determining whether a speaker phone is in use, wherein the controller selects one of the first and second voice input paths according to whether the speaker phone is in use.

Abstract: A training sequence is pre-filtered in a radiocommunication system having an emitter in the form of an antenna device with several antenna systems, thereby making it possible to transmit the training sequences through a pre-filter to said antenna systems side for reradiation by the emitter. Estimation enabling to form the properties of radio transmission channels described by spatial correlations is formed. The prefilter is dimensioned according to the correlations, thereby minimizing the error value of an algorithm used for estimation the channel on a reception side.

Abstract: A method for the performance testing of an echo canceller including the steps of transmitting a test signal to the echo canceller, recording an echo energy signal output from the echo canceller as a result of the test signal, measuring the energy and duration of the echo energy signal and calculating a performance score for the echo canceller based on the measured energy and duration of the echo energy signal, wherein the test signal transmitted to the echo canceller has a plurality of discrete frequency band segments of white noise representing sub-bands of an overall bandwidth ranging from about 0 kHz to about 3.5 kHz. The test signal preferably has four discrete frequency band segments of white noise, wherein each discrete frequency band segment of the test signal is repeated in succession, whereby the test signal has a total of eight segments.

Abstract: Disclosed methods and systems measure acoustic responses to training signals activated prior to communication sessions. Profiles related to the acoustic responses are saved and adapted during communication sessions. Training signals may have uniform frequency distributions over a frequency range and may be in response to user inputs, timeouts, or predetermined events. In the next excessive divergence is detected, an adapted profile may be substituted by an original, trained profile.

Abstract: In one embodiment, the presence of double talk (DT) is detected in a telecommunications network having a near-end user and a far-end user. The energies of both (1) a signal received from the far-end user by the near-end user and (2) a signal to be communicated from the near-end user to the far-end user are computed. An echo return loss (ERL) estimate is calculated based on the energy calculations, and a preliminary decision is made as to whether DT is present based on the ERL estimate and the energy calculations. If DT is detected, then a counter is set to a hangover value. If DT is not detected, then the counter is reduced. This process is repeated, and, for each iteration, a final decision as to whether DT is present is made based on the counter value.

Abstract: The present invention provides a network apparatus capable of canceling far-end crosstalk (FEXT). When the network apparatus is under a training mode, hard data is provided to a FEXT canceller for performing FEXT cancellation. When the network apparatus is under a data mode, soft data is provided to the FEXT canceller for performing FEXT cancellation as well. Therefore, FEXT is effectively canceled, and consumption power of the network apparatus is saved.

Abstract: The invention concerns a method, a network element and a computer program product for monitoring the quality of a real-time communication (9) in a packet network (1) comprising at least two test points (3, 4). A packet stream pattern (22) is accessed and injected at a first test point (3). After transmission of the packet stream pattern (22) through the packet network (1), a degraded packet stream pattern (23) is received at a second test point (4). Characteristics of the degraded packet stream pattern (23) are determined and compared with corresponding characteristics of the packet stream pattern (22) injected at the first test point (3). Based on the comparison, data concerning quality degradation caused by transmission over the packet network (1) is evaluated.

Abstract: A second output transmission signal (“TX2”) added to a line driver is a scaled version of the main output transmission signal (“TX1”). TX2 is scaled from TX1 by a variable scale factor K. An adaptive hybrid circuit subtracts TX1 and TX2 from a line signal carrying both a line transmission signal and a line received signal (“RX”). A programmable impedance Ztune is coupled between the TX2 output of the line driver and the RX output of the adaptive hybrid circuit. A transmission echo in the output RX signal is measured. K and Ztune are then adaptively tuned to minimize the transmission echo. The hybrid in this case becomes a 4-port network, one port specifically added to adaptively cancel the transmission echo in the RX output of the adaptive hybrid circuit. Alternatively, the hybrid may be a 3-port hybrid including variable impedances to cancel the line transmission signal.

Abstract: A method and apparatus for adapting dual filters is disclosed. In one aspect, a method may include transforming a signal, adapting a first adaptive filter based on the transformed signal, estimating a delay of an impulse response based on the adaptation of the first filter, delaying a signal based on the estimated delay, and adapting a second adaptive filter based on the delayed signal. In one aspect, an echo or other unwanted signal may be reduced or cancelled based on the adaptation of the second filter.

Abstract: An apparatus and methods supporting improved echo cancellation in a packet network is disclosed. An embodiment of the present invention may permit a split-band communication system operating in a narrowband mode to provide improved suppression of hybrid echo generated by the conversion of signals from a packet network to a two-wire analog circuit. By detecting the presence of signal characteristics outside of the relatively narrower bandwidth to be communicated, such an embodiment may more accurately detect the occurrence of speech received from a party on a relatively wider bandwidth communication circuit. The accurate detection of speech permits more effective suppression of any hybrid echo remaining after echo cancellation. An embodiment of the present invention may also have application in other systems that detect signals received via a path having a bandwidth greater than that to be transmitted.

Abstract: A method and apparatus to perform buffer management for media processing are described.

Abstract: Device and method for measuring a talking quality of a communication link in a communications network (10). The device comprises measurement means (22; 31, 36) connected to the communication link, which are arranged to subject a degraded speech signal s?(t) with respect to a reference speech signal s(t) to an objective measurement technique for measuring a perceptual quality of means are arranged for producing a quality signal (q) which represents an estimated value concerning the talking quality degradation. The degraded speech signal comprises a returned signal r(t). The measurement means (22; 31, 36) are arranged to execute the objective effects in consequence of noise present in the returned signal. The objective measurement technique comprises the determination of a threshold noise level by determining a local minimum value of the degraded speech signal s?(t).

Abstract: Facsimile communication is correctly performed even when an echo is generated in a communication line having a delay, by handling an echo signal in such a manner that when an echo of a CFR signal (according to the ITU-T recommendation V.21) transmitted from a receiving communication apparatus is received by the receiving communication apparatus, the echo signal is not recognized as a carrier of a picture signal and training data is not adjusted on the basis of the received echo signal, thereby making it possible to receive a correct short training/picture signal which arrives thereafter. A facsimile communication procedure includes storing training information when long training information is received, detecting success in receiving short training information, detecting high-speed data, setting the stored training information into the modem, and changing the receiving operation in response to detection of short training information and high speed data.

Abstract: A method of improving convergence of an echo canceller in a full duplex speakerphone, wherein the echo canceller includes LEC (Line Echo Canceller) and AEC (Acoustic Echo Canceller) portions, comprising the steps of capturing coefficients during operation, storing the coefficients, and utilizing the stored coefficients as default values during start-up of a subsequent call. According to the method of the present invention, the amount of echo cancellation necessary to provoke a save of the coefficients decreases with time when it is not achieved by the system despite the presence of a reference signal (i.e. speakerphone signal).

Abstract: A communication circuit includes a near end replication transmitter and a hybrid having an input in communication with an output of the near end transmitter. A high pass filter is responsive to the near end replication transmitter. A subtractor subtracts an output of the high pass filter from the output of the near end transmitter and an output of the hybrid. A near end receiver is responsive to an output of the subtractor. The near end replication transmitter is adjustable and includes a current generator in communication with an adjustable load.

Abstract: Apparatuses, systems, and methods for a multi-carrier communication system that detects and reduces an echo from a non-linear element present on the transmission medium. In an embodiment, a training period is established between a first transmitter-receiver device and a second transmitter-receiver device in the discrete multiple tone system that separates communication signals into two or more separate frequency bands. Noise caused by an echo generated by a non-linear element present on the transmission medium is detected during the training period. The significance of the non-linear echo contribution to the overall ambient noise level present in the system may be determined.

Abstract: A high-speed modem operates at speeds as high as 64 kbps in both the downlink direction from a digital modem to an analog subscriber and at an increased speed in the uplink direction from the analog subscriber back to the digital modem. Known systems provide a 56 kbps connection in the downlink direction but only provide for as high as a 33.6 kbps connection in the uplink direction. The present invention centers on the development of apparatus, systems, and methods for remote-echo cancellation whereby signal processing in the modem endpoints is used to remotely cancel an echo component at the input to a network-interface's ADC. Heretofore, this echo component has limited the achievable uplink data rate. Hence the present invention enables symmetric 56 kbps modem connections using POTS lines or the POTS channel within a DSL when line conditions warrant.

Abstract: Rapid identification and modeling of transmission media channel characteristics of a communications system using a correlation based technique. The technique provides a known training sequence used to generate a known quantity that operates on an observed or measured received signal, which is a function of the training sequence and the channel's impulse response, to give an estimate of the model of the channel. The technique decouples the training sequence from the observed or measured output, leaving the estimated impulse response. The impulse response of the transmission media channel is rapidly computed and processed to set the initial values of filter coefficients, for example, an echo canceller and an equalizer, in the communications system. Once the coefficients are initialized, if needed, a standard technique, such as least mean square (LMS) correlation, can be used to fine-tune the coefficients to converge on or model the transmission media channel's characteristics.

Abstract: Systems and methods for reducing transmit echo in a transceiver are disclosed. A hybrid echo canceller includes a limited tap length FIR filter to cancel short-term echo, while an interpolated filter is used to cancel the long-tail echo. The limited tap length FIR filter adapts and calculates coefficients for each adapted tap. Taps of the interpolated filter, on the other hand, are adapted but coefficients are calculated for a subset of the taps. Various interpolation schemes may be applied to the calculated coefficients to associate a coefficient with each tap of the interpolated filter. The technique presented produces an effective filter length of N taps with a reduction in computation and signal processing resources. Preferred embodiments of the echo canceller may be construed as methods for reducing transmit echo.

Abstract: Adaptive filtering algorithm training signals incorporate adaptation-enhancing signals having properties, such as spectral whiteness and rapidly decaying auto-correlation between samples, which allow the adaptive filtering algorithms to converge more quickly as compared to conventional algorithms. Exemplary adaptation-enhancing signals are incorporated such that the training signals are not perceptibly altered as compared to conventional training signals. For example, in a hands-free telephony application, an adaptation-enhancing signal according to the invention is dynamically tailored so that it is masked by a loudspeaker signal (the conventional training signal) and is thus inaudible to hands-free telephone users.

Abstract: A recently received portion of a transmit signal is utilized, and a pitch period of the received signal is determined. Then, the determined pitch period is utilized to search for similarities in the originally transmitted signal. This searching is done over a range of delays. Once the optimal delay is determined, it is then utilized as the delay between the transmitted signal and the received signal. Once this delay is known, the received signal can be time-aligned with the delayed signal.

Abstract: Determining the time delay between a transmitted signal and an echo. Then, the echo canceller is adjusted by the delay amount so that the echo canceller tail length is relatively short.

Abstract: A modem including an echo canceller adapted to determine locations of far-end echo sources. The echo canceller is adapted to send a signal to turn off network echo suppressors and enter a training mode. A training signal at a predetermined modem training frequency is sent from the modem to the second modem in the link. The return signal is then sampled by the sending modem. Any far-end echoes manifest themselves as sine waves at the modem training frequency, delayed in time. The time difference between the peak of the training signal and the echo signals is used to determine the echo delay.

Abstract: A cancellation system comprises a channel circuit (11) for each noise source, such as echo in a particular cable pair. There are only eighty taps per channel, in two blocks (n_echo_a, f_echo_a). Each block is preceded by a variable delay line comprising blocks of registers cascaded so that a delay value of 0 to 40 clock cycles can be chosen. The delay value is determined by determining an optimum position for each tap block. This is achieved by determining a maximum coefficient sum for a number of windows. Taps from other channels are used during training, so that there is a total of 160 taps for each channel during training to enable the optimum positions to be determined.

Abstract: A modem incorporating apparatus and methods to achieve computationally efficient echo cancellation. The apparatus include a cyclic echo synthesizer sub-canceler in the time domain and a echo canceler in the frequency domain. The method includes generating a cyclic echo synthesizer signal using a sub-canceler structure, adding the cyclic echo synthesizer signal to a receive signal in the time domain, generating an echo cancellation signal, and subtracting the echo cancellation signal from the receive signal in the frequency domain. The apparatus and methods may be used for echo cancellation in an asynchronous digital subscriber line (ADSL) modem using discrete multi-tone (DMT) technology.

Abstract: A method of converging a step size control for an adaptive filter of a communication channel including: (1) initializing a nominal step size value and a penalty point value; (2) combining the nominal step size value and the penalty point value to generate a step size value; and (3) dynamically changing the step size value in response to a characteristic measure of a quality of the communication channel. The step size value is changed by adjusting the nominal step size value, the penalty point value, or both. In a preferred embodiment the penalty point value is adjusted dependant on: (1) a tone originating from the far end (2) full convergence (3) the power level of a residual error signal (4) the channel's near-end background noise and/or (5) weak double-talk in the communication channel. The nominal step size value is adjusted when an achieved initial combined loss is about 15 dB or greater and is reset by divergence.

Abstract: In a conventional device for extracting voice features accurately without being influenced by noises, such as a voice recognition device, usually an input voice signal is processed first by a noise reduction system having the tap length N, and the result is FFT-processed by L-points, and then the power spectrum vector is calculated; accordingly, a one time operation requires N multiplications and (N?1) summations. The voice feature extraction device according to the invention receives a voice signal including noises from a microphone, which is processed by a window function operation unit, and thereafter FFT-processed by an FFT operation unit by L-points. A power calculation unit calculates a power spectrum vector of the input voice signal. However, a noise reduction system determines in advance a filter coefficient of this system and processes the coefficient to calculate a noise reduction coefficient, and the power spectrum vector is processed by this noise reduction system.

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: 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: 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: In one embodiment, a mobile station such as a dual-mode, AMPS and CDMA, handset communicates with an AMPS base station in a wireless communication system. The mobile station includes an acoustic echo canceller, which can detect acoustic echo, for example, feedback from the handset speaker to the handset microphone, during communication between the mobile station and the base station, and cancel or eliminate the acoustic echo. The mobile station also includes a network echo suppressor coupled to the acoustic echo canceller. For example, the network echo suppressor can read a parameter set by the acoustic echo canceller. The network echo suppressor attenuates or mutes a network echo caused by portions of the communication returning to the mobile station from the base station after a network propagation delay. Coupling the network echo suppressor to the acoustic echo canceller ensures proper interaction between the network echo suppressor and acoustic echo canceller.

Abstract: A two-step training method for the estimation filter in the echo cancellation (EC) path of the analog front-end (AFE) circuit for a modem, such as an asymmetric digital subscriber line (ADSL) modem. During the first step, the transmit (TX) path is turned off and a digital TX signal (e.g., a pseudo white gaussian noise signal) is applied to the EC path essentially bypassing the EC estimation filter. During the second step, the EC path is turned off and a digital TX signal (e.g., the same pseudo white gaussian noise signal) is applied to the TX path. Coefficients for the EC estimation filter are then generated based on the digital RX signals recorded during the two training steps. In particular, the recorded digital RX signals are transformed to the frequency domain, where one is divided into the other. The resulting digital signal is then transformed back to the time domain, where it is used to generate the coefficients for the EC estimation filter.

Abstract: A method of improving convergence of an echo canceller in a full duplex speakerphone, wherein the echo canceller includes LEC (Line Echo Canceller) and AEC (Acoustic Echo Canceller) portions, comprising the steps of capturing coefficients during operation, storing the coefficients, and utilizing the stored coefficients as default values during start-up of a subsequent call. According to the method of the present invention, the amount of echo cancellation necessary to provoke a save of the coefficients decreases with time when it is not achieved by the system despite the presence of a reference signal (i.e. speakerphone signal).

Abstract: A packet voice transceiver adapted to reside at a first end of a communication network and to send and receive voice packets to and from a second packet voice transceiver residing at a second end of the communication network. The transceiver includes a voice encoder, a packet transmitter, a packet receiver, a voice decoder and a far-end echo canceller. The voice encoder receives an ingress audio signal and encodes the audio signal to produce an ingress packet voice signal. The packet transmitter transmits the ingress packet voice signal over the network to the second packet voice transceiver. The packet receiver receives an egress packet voice signal transmitted over the network by the second packet voice transceiver. The voice decoder decodes the egress packet voice signal to produce an egress audio signal. The far-end echo canceller reduces echo that is present in the egress audio signal and that originated at the second end.

Abstract: A speaker-phone that is operable to perform system change detection, double-talk detection and if desired, optimal step-size control. The invention differentiates between system change and double-talk and is operable to these two situations differently. The invention does not rely solely on the energy measurements that are employed by conventional speaker-phones. Highly reliable system change detection is offered when compared to conventional speaker-phones. The direction and the amplitude of the system change is measured with very good detection probability in the invention. For double-talk detection, the invention does not rely on assumptions that the far-end echoes are of lower amplitude that the near-end signal in performing double-talk detection. The invention performs double-talk detection within a large diversity of echo-paths and background noise levels. A designer may tune the speaker-phone system to ensure proper double-talk detection near low levels of the near-end signal.

Abstract: A method and noise reduction apparatus comprises a microphone array including a plurality of microphone elements for receiving a training signal including a plurality of training signal samples, and a working signal including a plurality of working signal samples, and at least one frequency domain convertor coupled to the plurality of microphone elements for converting the plurality of training signal samples and the plurality of working signal samples to the frequency domain. A signal spatial correlation matrix estimator is coupled to the at least one frequency domain convertor for estimating a signal spatial correlation matrix using the converted plurality of training signal samples. An inverse noise spatial correlation matrix estimator is coupled to the at least one frequency domain convertor for estimating an inverse noise spatial correlation matrix using the converted plurality of working signal samples.

Abstract: An echo canceler includes an adaptive filter that adapts to changes in an echo path, a double-talk detector, and an echo path change detector. The echo path change detector estimates the loss on the echo path, thereby distinguishing true double-talk from apparent double-talk detected by mistake because of a change in the echo path. The adaptive filter continues normal adaptation during the apparent double-talk state when echo path change is also detected. The necessary conditions for detection of echo path change preferably include a small separation between the estimated loss on the echo path and a long-term smoothed value of the estimated loss. The echo path change detector is useful in, for example, the cancellation of line echo in telephone switching systems.

Abstract: A method of canceling echoes in a telecommunications system wherein an exchange of information takes place between a local subscriber and a subscriber at the remote end of a transmission link and at least one subscriber is assigned an echo canceller, the parameters of which are set as a function of an echo delay time (i). The signs of the signal x(t) transmitted by a subscriber and the signal y(t) received by the subscriber can be determined at equidistant time intervals (Ti) so that sign sequences arise which are stored and compared with one another, and in the event of a direct correspondence or a correspondence as a result of an inversion of the sign sequences of the received signal y(t) and of the transmitted signal x(t) the received signal y(t) is detected as an echo and the echo delay time (i) is calculated.

Abstract: The step sizes for tap positions of an adaptive filter (124) in an echo canceller (125) for canceling an echo signal are individually selected based upon a profile of the echo environment. A training signal (112) is injected into the echo canceller and to the echo path during a training interval, or period. The adaptive filter profiles the echo path during the training interval. Respective step sizes &agr;[k] for the tap positions are generated as a function of the echo profile so generated.

Abstract: A communication circuitry for providing effective detection of tones in a communication network. The communication circuitry comprises filtration circuitry, summation circuitry, detection circuitry, and interface circuitry. The filtration circuitry is coupled to the summation circuitry and is configured to receive a communication, process the communication to estimate an echo return in the communication, and provide the estimated echo return to the summation circuitry. The summation circuitry is coupled to the detection circuitry and configured to receive the estimated echo return from the filtration circuitry, receive a tone transmission and echo return from the interface circuitry, subtract the estimated echo return from the tone transmission to generate a substantially pure tone, and provide the substantially pure tone to the detection circuitry. The detection circuitry is configured to receive the substantially pure tone and process the substantially pure tone to perform a programmed operation.

Abstract: An method and a device for echo suppression in a handsfree apparatus, particularly for a telephone is disclosed. With the aid of a control unit, control signals are generated from the signal of the far-end subscriber, the output signal of the loudspeaker-room-microphone system and the output signal of an adaptive filter used as reference, the control signals having an amplitude and a time response dependent on the speech mode. Using the control signals, the amplifications VE, VS of controllable amplifiers disposed in the receiving and transmitting paths are adapted to the speech mode, thus reducing the residual echo. The stepless transition of the amplifications from a quiescent value to a value attenuated with the factor and having an exponential time characteristic in response to a change of speech mode, provides an impression of natural speech.

Abstract: A method and apparatus are disclosed for canceling acoustic echo generated during transmission of text information in a communication system supporting a TTY/TDD service. When an mobile-to-land call is established between a mobile subscriber and a PSTN subscriber, a decoder notifies an encoder of detection of TTY/TDD text in a BS vocoder. The encoder then transmits a packet having silence information, which prevents acoustic echo reproduction of the text in the TTY/TDD device.

Abstract: A circuit arrangement for controlling audio signal transmissions for a communications system that includes a microphone and a video camera. The arrangement comprises a video processor configured and arranged to receive a video signal from the video camera, detect movement of an object in the video signal, and provide a motion-indicating signal indicating movement relative to the object. An audio processor is coupled to the video processor and is configured and arranged to modify the audio signal to be transmitted responsive to the motion-indicating signal. In another embodiment, a video signal processor is configured and arranged to receive a video signal from the video camera, detect mouth movement of a person and provide a mouth-movement signal indicative of movement of the person's mouth.