Abstract: A system for driving a first signal onto a wireline includes a driver and feedback circuitry. The driver drives a deterministic signal onto the wireline with an unknown impedance load. The feedback circuitry measures a quality of the output signal from the wireline and modifies a signal strength of the first signal based on the quality of the output signal. The driver then drives the first signal onto the wireline with the modified signal strength.

Abstract: The present subject matter is directed to an apparatus and methodology for monitoring for the occurrence of use of unauthorized telecommunications equipment within a designated area. The present subject matter has particular utility to the corrections environment in that it discloses a methodology for detecting and reporting the unauthorized operation of cellular telephones within a corrections facility. The present technology may be used advantageously in combination with inmate telephone systems to transmit information to appropriate personnel in the form of email messages and/or voice communications by way of telephone local or corrections facility external telephone lines. The present technology also provides for recordation and storage of time, date and location information for detected events.

Abstract: In a voice activity detection (VAD) device a method for defining tone signals comprises defining a threshold for zero amplitude change, calculating a zero crossing rate of a signal, extracting a set of parameters from a plurality of duration periods of the signal, defining a tolerance threshold between the plurality of duration periods when a zero amplitude change occurs, calculating a maximum difference between the plurality of duration periods, and comparing the maximum difference with the threshold. The method is implemented in the International Telecommunications Union (ITU) recommendation G.729 Annex B VAD.

Abstract: Acoustic shock is reduced by attenuating an input signal based on tones detected through frequency domain analysis. The spectrum of the input signal is obtained. A relative energy signal includes a plurality of relative energy elements, each representing the relative energy in a corresponding frequency bin of the input signal spectrum. A difference signal includes a plurality of difference elements, each representing a difference between a corresponding frequency bin value and an adjacent frequency bin value. A plurality of detection signals are determined, each detecting the presence of a sound element in the input signal based on at least one of the relative energy signal and the difference signal. The detection signals are combined to produce an attenuation signal for attenuating the input signal.

Abstract: A signalling tone detector for use in a communications network for the detection of dual frequency multi-tone (DTMF) pairs of signal tones in a time division multiplex (TDM) signal. The detector comprises first and second arrays of adaptive notch filters corresponding to the rows and columns of a subscriber's pushbutton key set. Each said notch filter responds to a respective signal tone by the generation of a corresponding output signal. A logic circuit identifies from a combination of output signals from the adaptive notch filters the presence or absence of a pair of signal tones and, when the presence of a pair of signal tones has been identified, for decodes that pair of tones to corresponding digit information. The detector is used in an arrangement for compressing and packetising TDM traffic for transport over a connectionless network. To prevent distortion, the DTMF tones are decoded to digit information prior to transport over the connectionless network.

Abstract: In some embodiments, a method includes detecting a tone in each data frame of a sequence of telephony signal data frames. A first data frame of the sequence of telephony signal data frames may be transmitted immediately after detecting the tone therein. Transmission of a last one or last ones of the sequence of telephony signal data frames may be deferred. It may then be determined whether the tone is present in a next data frame that immediately follows the sequence of telephony signal data frames. If it is determined that the tone is not present in the next data frame, the last one or ones of the sequence of data frames and the next data frame may be transmitted. If it is determined that the tone is present in the next data frame, a respective replacement data frame may be transmitted in place of each one of the last one or last ones of the sequence of data frames and in place of the next data frame.

Abstract: A noise calculation mechanism is incorporated into a cadence tone detector which upon a miss in either a energy or silence interval allows for retention of those periods corresponding to noise and augments the appropriate energy and silence interval.

Abstract: The present invention provides a tone detector that is capable of performing accurate tone signal detection in a short period of time. Specifically, the tone detector according to the present invention includes: a control unit that measures the tone signals using a plurality of channels having a predetermined measuring time interval, which are shifted by a fixed time period, and reads out the tone signals stored in a memory unit for each of the measuring time intervals; detection processing units that determine the characteristic quantity of the tone signals read out by the control unit; and a tone determination unit that identifies the tone signal for each of the plurality of channels based on the characteristic quantity determined in the detection processing units. In this tone detector, the tone signals are measured using a plurality of channels wherein the measuring time interval of each channel is shifted by a fixed time period after which the tone signal is identified.

Abstract: A tone processing method and communications system which reduce the probability of falsely detecting modem and facsimile communications that occur on a communications link. The link connects a calling endpoint to an answering endpoint. In a preferred embodiment, when the answering endpoint goes off-hook in response to receiving a call from the calling endpoint, an elapse of time is measured while monitoring the link. If a predetermined amount of time elapses without detecting at least one tone on the link, tone detection criteria is modified to reduce tone detection sensitivity, or to ignore tones altogether. In another embodiment, the tone detection criteria is similarly modified if voice activity is detected on the link. In yet another embodiment, when tones and voice activity occur at different times during a call, at least one characteristic is modified to optimize the link for the type of communications occurring on the link.

Abstract: The present invention relates to the field of tone detection and, more particularly, to the detection of dual tone multi-frequency (DTMF) tones in software based telecommunications systems. As modem telecommunications systems are becoming increasingly software based and typically require only a minimum of physical hardware, much of the necessary telecommunication functionality is now provided by software functions running on powerful computer servers. A common function which is required to be performed by telecommunications systems is that of dual tone multi-frequency (DTMF) detection. Accordingly, the present invention aims to provide an efficient software-based DTMF detection system that satisfies the ever increasing need for efficient software functions.

Abstract: The invented method involves one or more gateways sniffing the voice channel during the voice mode. If it is determined that V.8bis signals are being initiated, then the gateway breaks these exchanges by suppressing such signaling, thereby avoiding the above-described detrimental effects. Modem relay communications then are allowed to proceed. Briefly, the method and apparatus involve monitoring a call during a voice mode phase for an initiating signal representative of the defined signaling, the monitoring being performed by a local gateway and, if such an initiating signal is detected during the monitoring, then suppressing such detected signaling in such manner that the signaling does not reach the remote gateway. Preferably, the monitoring is for an initiating signal characterized by a dual tone of defined frequency and duration of approximately 1375 Hz and 2002 Hz for a duration of approximately 400 ms or 285 ms, in agreement with the ITU-T Recommendation V.

Abstract: Call progress analysis is performed in a telephone system employing different in-band signaling plans are used. From address information for a call destination in a call initiation message, it is determined which type of in-band signaling plans is utilized by equipment associated with the call destination, for example by examining country codes in a dialed telephone number. Based upon the determined signaling plan type, a corresponding type of call progress analysis resource is selected and allocated for use with the call. The analysis resource may include a digital signal processor (DSP) programmed with an analysis routine tailored to the determined signaling plan. The DSP may be pre-programmed with such a routine or may be loaded at call time with analysis parameters appropriate to the signaling plan. The telephone system may employ a packet network and packet-based telephony transmission, a media gateway controller or a Session Initiation Protocol (SIP) proxy server, an a media server.

Abstract: A method and apparatus for DTMF detection and voice mixing in the code-excited linear prediction (CELP) parameter space, without fully decoding and reconstructing the speech signal. The apparatus includes a Dual Tone Multiplexed Frequency (DTMF) signal detection module and a multi-input mixing module. The DTMF signal detection module detects DTMF signals by computing characteristic features from the input CELP parameters and comparing them with known features of DTMF signals. The multi-input mixing module mixes multiple sets of input CELP parameters, that represent multiple voice signals, into a single set of CELP parameters. The mixing computation is performed by analyzing each set of input CELP parameters, determining the order of importance of the input sets, selecting a strategy for mixing the CELP parameters, and outputting the mixed CELP parameters.

Abstract: A dual hysteresis signal detection circuit is proposed for detecting a duration of a signal with two hysteresis comparators. There is a first band pass filter for inputting the signal and outputting the signal having a first frequency. A first hysteresis comparator electrically couples to the first band pass filter for comparing with the first frequency of the signal to output a first square wave signal according a first high voltage and a first low voltage. A second hysteresis comparator electrically couples to the first band pass filter for comparing with the first frequency of the signal to output a second square wave signal according to a second high voltage and a second low voltage. A first detection circuit electrically couples to the first hysteresis comparator for detecting a part of the signal having the first frequency that is higher than the first high voltage and lower than the first low voltage to output a first detection signal according to the first square wave signal.

Abstract: Detectors determine the presence of valid sinusoids for DTMF, MF-R1 and MF-R2 protocols for encoding dialed digits. The detectors split electrical signals into subbands. Energies within the subbands are analyzed to determine a presence of sinusoids corresponding to frequencies of dialed digits. In one embodiment, the detectors comprise a PS-IIR filter to split the electrical signal into the subbands. The detectors further comprise at least one bank of filters, such as notch filters, corresponding to the number of possible relevant frequencies within the respective subbands. The detectors further comprise detection logic comprising tests, which may include analyzing the output(s) from the bank of filters. Optionally, a preclassifier is employed to predetermine which filters in the banks of filters are to be executed. The detectors, typically deployed in digital signal processors, allow for an increase in the density of detectors and provide robust performance in talk-off situations.

Abstract: A ringback detector determines whether ringback by comparing measurements of a characteristic of the received signal, such as the energy of the received signal, to a threshold. The threshold is set initially to a low value and then updated based on the measurements of received signal. The measurements are then compared to the threshold to determine whether ringback is present. An output signal indicative of ringback is generated when ringback is present.

Abstract: A push-button signal receiving device and a gain control method whereby error in validity determination of a received signal that accompanies the insertion of an AGC circuit can be prevented. An input bush-button signal is amplified by amplifying circuit and separated into signals of low- and high-frequency bands by first and second band-pass filters, respectively. Dialed number identifying circuit detects the frequencies of the separated signals to identify the dialed number, determines validity of the received push-button signal, and outputs the identified dialed number in accordance with the result of validity determination. Level detecting circuit detects the level of the output signal from the amplifying circuit. Gain control circuit controls the amplification gain of the amplifying circuit in accordance with the detected signal level, and holds the value of the amplification gain of the amplifying circuit while the received push-button signal is judged valid by the dialed number identifying circuit.

Abstract: Before any supply of remote power to a telecommunications terminal connected to a local area network, the Ethernet equipment must recognize the power class of the terminal by measuring a specific electrical signature of the terminal via their interconnection. If the Ethernet equipment is unable to supply the required power, then it will send a specific signal via the interconnection which will activate an alarm on the terminal. The possibility to be alerted by a specific alarm from the terminal if no remote power can be supplied to it, will advantageously inform the terminal user of the problem and allow the user to look for an alternative.

Abstract: A passive coupling structure constructed using printed circuit board traces is used to separate the low and high frequency components of an incoming digital signal. The low and high frequency components of the signal are sent to separate receivers on an integrated circuit. The low frequency receiver may be a conventional level based receiver. The high frequency receiver is a Schmitt-trigger with hysteresis around a DC level or two comparators with separate reference voltages. The outputs of these receivers are combined to produce a receiver output that has increased reliability and noise immunity.

Abstract: Performing tone detection for an amount of time that is calculated from the tones that the detector is designed to detect.

Abstract: A communication apparatus connected to a PBX and an ATM network is provided with a DTMF signal detecting portion for detecting whether or not a DTMF signal is contained in a voice signal from the PBX, a DTMF signal monitoring portion, a DTMF cell generating portion for coding and sending out a DTMF signal, a DTMF cell decomposing portion for decoding a coded DTMF signal and a DTMF signal generating portion for generating a DTMF signal on the basis of the information content of a decoded DTMF signal and sending out this DTMF signal to the PBX, and the transmission side communication apparatus codes a DTMF signal in a specified form and transmits the DTMF signal and the reception side communication apparatus decodes the coded DTMF signal and, on the basis of this content information, restores the DTMF signal in a DTMF signal generating portion.

Abstract: A method and apparatus for an automatic ring again feature on a telephone set for a user that answers a telephone call not intended for that user is disclosed. If a user has answered an incoming telephone call not intended for that user, a “Ring Again” feature on the telephone set is activated. In response to the Ring Again feature being activated, parallel telephone sets will ring again to allow a different user to answer the call or, alternatively, another device, such as an answering device, to answer the call.

Abstract: A tone transmission part transmits a tone signal. A tone signal detection part detects data representing an echo signal of the tone signal transmitted by the tone transmission part, and detects data representing a predetermined tone signal targeted to be detected. The tone signal detection part also detects data representing tone signals of all of input signals. A tone judgment part excludes the data representing the echo signal from the data representing the tone signals of all of the input signals so as to judge a detection of the predetermined tone signal.

Abstract: A signal detector for detecting a signal having a first nominal frequency, F1 and a second nominal frequency F2, the signal intermixed with an interfering signal to form a composite signal, the signal detector including a first and a second band pass filter centered at F1 and F2 for filtering the composite signal to provide an F1 and F2 signal; a parameter estimator for determining an F1 and F2 period for the F1 and F2 signal for a sequence of frames and an average period shift (APS) for a current frame and a plurality of earlier frames; a metric calculator for calculating a metric that corresponds to the F1 and F2 period and the APS; and a decision processor for deciding whether the signal has been detected based in part on a comparison of the metric and a threshold.

Abstract: A communication apparatus is used to interface signals with any one of a plurality of telephony networks having different impedances. The apparatus includes memory, a processor, a digital-to-analog (D/A) converter, and an interface port. Different sets of impedance control values are stored in the memory. The processor is configured to select one of the sets of impedance control values and to serially transmit the selected set of impedance control values during a communication session. The D/A converter is configured to receive the selected set of impedance control values from the processor and to transmit analog signals based on the selected set of impedance control values. The interface port is configured to interface signals with a communication connection of a telephony network.

Abstract: A signal classifier decomposes a subject signal into subbands. The signal classifier then analyzes the subbands for a presence of energy and uses detection logic to classify the energy as being representative of a frame of a signal using one of the following protocols: DTMF, MF-R1, ANS (V.25), LEC-DIS, V.21, or AA (i.e., telephone, facsimile, or modem). The detection logic is expandable to detect future protocols. The classifier may employ a preclassifier to select a reduced number of notch filters from among plural notch filters at frequencies which sinusoidal signals composing the energy in the subbands of the protocols may be found. A look-up table having predetermined ranges of data corresponding to the frequencies of the sinusoidal signals may be used to reduce calculation times. By splitting the subject signal into subbands and using efficient filters, the classifier uses an order of magnitude fewer processor instruction cycles than previous classifiers.

Abstract: A multi-frequency tone detector with analysis window (i.e. filter size) chosen such that spectral nulls are located at adjacent frequencies of interest. The decision logic block of the tone detector uses the roll-off characteristics of the filter in conjunction with background noise to determine a threshold pass/fail for any tone that has deviated excessively from its nominal value. The foregoing aspects of the invention result in simple filter design (i.e. reduced order) relative to prior art tone detectors.

Abstract: Disclosed is an integrated tone detection processor for discriminating between tone and voice signals and determining the tones. The tone detection processor performs Automatic Gain Control (AGC) to normalize the power of the tone or voice signal. Further, the energy of the tone or voice signals are determined at specific frequencies utilizing a Goertzel Filter process. The tone detection processor determines whether or not a tone is present, and if a tone exists, determines the type of tone. Based upon determining the two maximum energy levels of the Goertzel filtered tone, whether the tone is a single tone, dual tone, silence, or other (e.g. speech) can be discriminated. The tone can then be identified by a user-defined dictionary of tones. Based upon various ON and OFF cadence checks in combination with the use of TONE ON and TONE OFF counters, tones can be declared.

Abstract: A plurality of Goertzel filters whose operating frequencies are distributed across the voice baseband are used to detect voice and control tones in a signal. Filters operating at frequencies of control tones and detecting that most of the signal energy occurs at those frequencies indicates presence of the control tones. At least three of the filters detecting that about 10% to 20% of the signal energy occurs at each of their operating frequencies indicate presence of voice. The total energy detected in the signal being below a noise threshold indicates presence of noise or silence.

Abstract: A method and apparatus for detecting a signaling tone within a communications channel, such as a telephone line, is presented. The energy level of the communications channel signal is measured at the frequency of the signaling tone and at one or more frequencies that are integer divisors of the signaling tone (i.e. at one or more subharmonics). The subharmonic energies are evaluated in determining whether the signaling tone is present. The technique can be implemented using a plurality of resonators and a comparator.

Abstract: The present invention provides a low power method and apparatus for detecting a signaling tone. The apparatus comprises a resonator which can be configured to resonate at a specified frequency, a controller for configuring the resonator, and a comparator for comparing the output of the resonator as configured by the controller. The method comprises configuring the resonator to resonate at a first frequency to generate an output, configuring the resonator to resonate at a second frequency to generate an output, comparing the outputs, and indicating the presence of a signal if the output of the resonator configured to resonate at a first frequency exceeds the output of the resonator configured to resonate at a second frequency by a predefined amount.

Abstract: In known telephone subscriber end stations a caller_ID IC detects a tone alerting signal TAS alerting that successive caller_ID information can be received for displaying on a display of the phone. The known station applies narrow frequency band filters to detect tones indicating the end of TAS. Such a detection is not flexible as it can only be used for a specific caller_ID signal protocol. A flexible detector is proposed which can easily be adapted to widely varying protocols and which can also be used for other purposes such as the detection of power drops in an FSK signal. The detector comprises means for determining a time-domain signal representing the signal energy of a signal on the subscriber line in a predetermined time interval.

Abstract: A DFT is used to compute the magnitude and phase of the frequencies desired to be detected in a frame of sampled data by performing 2 dot products for each such frequency. The two dot products are calculated using the samples in the frame and an equal number of equally spaced cosine and sine coefficients for each frequency to be detected.

Abstract: A system and method for determining DTMF coefficients stores a plurality of reference templates, at least some of said reference templates representative of likelihood ratios. A plurality of LPC coefficients is received. The LPC coefficients are representative of an input signal. The system and method determines a plurality of current likelihood ratios based, at least in part, upon the LPC coefficients. The system and method also determines an initial tone based, at least in part, on the minimum of the current likelihood ratios and the minimum of the reference likelihood ratios. A plurality of LSF coefficients is received. The LSF coefficients are determined, at least in part, upon the input signal. The system and method verifies the validity of the initial tone based, at least in part, upon the LSF coefficients.

Abstract: A method of repeating a non-voice signal such as a dual tone, multiple frequency (DTMF) signal, by inserting a delay sequence of data values into an output data sequence of data values, a portion of the output data sequence following the delay sequence being the same as a corresponding portion of an input sequence of decoded data obtained from a low bit-rate speech decoder. The input sequence has at least one distorted non-voice sequence. The method provides for inserting a substantially undistorted non-voice sequence into the output sequence, the undistorted sequence being at least of substantially the same length as the distorted sequence, a portion of the output sequence following the undistorted sequence being the same as a corresponding portion of the input sequence, and the output sequence being substantially free of the distorted non-voice signal.

Abstract: A method of detecting frequency errors exceeding a predetermined limit in a sampled signal includes the step of determining a peak amplitude of the signal at a tone frequency for a first frame of samples of the sampled signals using a filter having a first amplitude versus frequency response. A peak amplitude of signal at the tone frequency is determined for a second frame of samples of the sampled signal using a filter having a second amplitude versus frequency response. A ratio between the peak amplitude of the first frame and the peak amplitude of the second frame is calculated and compared against a threshold to detect frequency errors exceeding the predetermined limit. Among other things, this method decouples the frequency error detection problem from the twist factor estimation problem.

Abstract: A filtering circuit is described for filtering out meter pulses of analog telephone communication, for example in analog modems. The circuit is mainly composed of resistors and capacitors and is configured as a double T element or a Wien bridge circuit. The filtering circuit is needed for attenuating interferences to such an extent that integrated circuits operating with low voltages are not overloaded.

Abstract: An apparatus for detecting a dual tone alert signal in a telephone system capable of at least off hook mode operation includes a processing channel for each tone. Each channel consists of a bandsplit filter for extracting the tone of interest and attenuating the other tone; a comparator for comparing the output of said bandsplit filter with a threshold value; and an adaptive threshold generator for generating said threshold value adapted to the amplitude of the output of said bandsplit filter to reject speech and music imitations. The apparatus offers improved talkdown and talkoff immunity.

Abstract: An apparatus and method are provided for decoding single-frequency or multi-frequency signals, such as DTMF signals, without the use of analog bandpass filters. The method of the present invention is equally applicable to any decoding of multi-frequency signals. The method is composed of a number of steps. First, an incoming (analog) signal is received and transformed into binary signals (1 or 0) at specific instances of time. The incoming binary signal is compared to a pre-defined expected (binary) signal at each time step. The incoming and expected bit values for each time step are then compared and the comparison result is stored as part of a frequency response table. The comparison values are then summed and, if the summed value exceeds a pre-defined threshold, the incoming and expected signals are declared a match. Otherwise, the signals are declared a mis-match.

Abstract: Devices, software and methods are provided for encoding DTMF signals for telephone connections between digital voice communication systems that use compression, such as wireless connections or network connections. First the twist of the DTMF signals is determined, and then it is determined whether the twist is within a mapped range of a remote decoder. If not, the signal is first balanced to change the twist, and then the balanced signal is encoded.

Abstract: For use with analog telecommunications equipment that responds to in-band stimuli, a system for, and method of suppressing an in-band stimulus and a telecommunications infrastructure employing the system or the method. In one embodiment, the system includes: (1) a stimulus detector, associated with the analog telecommunications equipment, that detects a presence of the in-band stimulus and (2) a stimulus suppressor, coupled to the stimulus detector, that alters the in-band stimulus to cause the analog telecommunications equipment to disregard the in-band stimulus.

Abstract: A method and apparatus for DTMF detection and voice mixing in the code-excited linear prediction (CELP) parameter space, without fully decoding and reconstructing the speech signal. The apparatus includes a Dual Tone Multiplexed Frequency (DTMF) signal detection module and a multi-input mixing module. The DTMF signal detection module detects DTMF signals by computing characteristic features from the input CELP parameters and comparing them with known features of DTMF signals. The multi-input mixing module mixes multiple sets of input CELP parameters, that represent multiple voice signals, into a single set of CELP parameters. The mixing computation is performed by analyzing each set of input CELP parameters, determining the order of importance of the input sets, selecting a strategy for mixing the CELP parameters, and outputting the mixed CELP parameters.

Abstract: A general purpose network tone detection method and apparatus that allows the precise and accurate recognition of North American tones (MF, DTMF (Dual-Tone Multifrequency), and CPT (Call Progress Tones)) and international MF-R2 tones as well as taking into consideration other common tones such as Calling Card Service Prompt and Recall Dial. Through the use of the Discrete Fourier Transform (DFT) on small time windows and by providing phase continuity between these windows, the results of the successive DFTs may be combined and processed by a second DFT computation. This second DFT allows higher frequency resolution without requiring the re-computation of the DFT from the time samples. The resulting effect is a tone receiver with both high time and frequency resolution which consequently leads to robust and accurate tone recognition systems conforming even to the most stringent specification while maintaining low computational requirements.

Abstract: A signal detector includes a transform unit and a post processing test unit. The transform unit is adapted to a transform unit adapted to receive at least first and second frames of input samples, determine a first plurality of energy values for the first frame based on a first set of transform coefficients, and determine a second plurality of energy values for the second frame based on a second set of transform coefficients. The post processing test unit is adapted to identify at least one target frequency based on the first plurality of energy values. The second set of transform coefficients is based on the target frequency, and the post processing unit is adapted to determine the presence of a first signal in the input samples based on the second plurality of energy values. A method for detecting a signal is provided. A first frame of input samples is received. A first set of transform coefficients is determined based on a first plurality of frequencies.

Abstract: A signal detector for detecting at least a first signal having a first frequency and a first minimum duration is provided. The signal detector includes a matched transform unit and an energy level detection unit. The matched transform unit is adapted to receive at least a first frame of time domain input samples at a sampling frequency and generate at least a first frequency energy value for the first frame based on at least a first subset of the time domain input samples. The first subset of the first frame has a width of less than about one half of the first minimum duration. The energy level threshold unit is adapted to compare the first frequency energy value to a threshold energy value to determine the presence of the first signal. A method for detecting at least a first signal having a first frequency and a first minimum duration is provided. The method includes receiving at least a first frame of time domain input samples at a sampling frequency.

Abstract: A method, apparatus, and system for detecting a tone.

Abstract: A calling party dials a called party, a no-answer status is received, and the called number is automatically redialed at intervals until receiving an answer status or reaching a maximum limit. Prompting a user for redial options may be included. A called party may be requested to select connection before the call is connected to the calling party.

Abstract: A system is disclosed for accurately detecting an alert signal. Improving detector accuracy decreases missed detects and false detects. In one example embodiment the detector monitors received telephone signals for an alert signal such as a CPE alert signal. In such a configuration, the invention processes the received signal prior to monitoring by the detector to remove or reduce unwanted echo, interference and/or other signal portions that may otherwise inhibit accurate detection of alert signals sent from a remote location. In one configuration, the invention performs echo suppression or cancellation on the received signal to eliminate or reduce echo, such as may be introduced by a hybrid.

Abstract: A method and device for decoding a sequence of signals in which information is derived, in part, from a duration of (a) one of the signals and/or (b) an inter-signal pause between two of the signals. The method and device may also be used to decode a signal to form decoded information, derived, in part, from a duration of the signal.

Abstract: A tone detector for a modem detects the presence of a tone, such as that sent during a retraining request, using a complex adaptive FIR filter of the form 1−z−1. The filter will detect the tone regardless of symbol rate.