Abstract: A fast-converging, computationally simple, method for recognizing a single frequency tone or a sinusoid in a signal without prior knowledge of the tone frequency. The method employs a second order or higher auto-regressive model and includes: (a) sampling the signal at a constant sampling rate, and, for each sample, recursively determining a finite number of correlation coefficients using a time-reversed, exponentially weighted, future sliding equivalent of the signal, wherein the correlation coefficients are determined using pre-existing values of the correlation coefficients determined in a previous iteration, a current sample of the signal and at least two consecutively previous samples of the signal; (b) periodically determining at least the second auto-regressive coefficient modeling the signal using the correlation coefficients; and (c) recognizing the presence of the tone based on the value of the second auto-regressive coefficient.

Abstract: In an emergency notification and rescue request system having an answer detector for detecting a call receiving party's answer to a telephone call, the answer detector comprises a level detector for outputting a first signal when a level of an audio signal on a telephone line is greater than a prescribed level and otherwise outputting a second signal which is different from the first signal, wherein an interval between adjacent prescribed state changes in the output signal from the level detector is computed every time the prescribed state change is detected, and the current and previous intervals are compared so that if such an event that the current and previous intervals do not substantially correspond to each other has occurred prescribed times consecutively, it is determined that no regular signals such as the busy signal or ring signal exist on the telephone line, i.e., the call receiving party has answered the telephone call.

Abstract: Reliably detecting voiceband signaling tones at a subscriber or network device in the presence of near-end and far-end speech occurs by eliminating, rather than balancing, near-end talk-off and by separately handling far-end talkoff and near-end talkdown. A tone detector is placed on the receive path of the device. One or more frequencies that comprise the tone to be detected by the tone detector are attenuated/removed from the near-end speech present on the send path of the device thereby preventing the near-end speech from talking-off the tone detector. Near-end talkdown and far-end talkoff are eliminated by utilizing two separate signal-to-guard ratios within the tone detector: a large signal-to-guard ratio to combat the effects of the far-end talkoff and a small signal-to-guard ratio to combat the effects of the near-end talkdown. The tone detector is switched between the two signal-to-guard ratios by predicting whether the near-end is speaking.

Abstract: This invention unifies a set of statistical signal processing, neuromorphic systems, and microelectronic implementation techniques for blind separation and recovery of mixed signals. A set of architectures, frameworks, algorithms, and devices for separating, discriminating, and recovering original signal sources by processing a set of received mixtures and functions of said signals are described. The adaptation inherent in the referenced architectures, frameworks, algorithms, and devices is based on processing of the received, measured, recorded or otherwise stored signals or functions thereof. There are multiple criteria that can be used alone or in conjunction with other criteria for achieving the separation and recovery of the original signal content from the signal mixtures. The composition adopts both discrete-time and continuous-time formulations with a view towards implementations in the digital as well as the analog domains of microelectronic circuits.

Abstract: A method for detecting a tone signal includes determining a correlative value of an input signal obtained for each frame of a predetermined length, determining an estimating expression that represents an output power of a second order FIR band elimination filter that uses the correlative value of the input signal as an input and a frequency thereof as a parameter, determining a frequency at which a minimum value of the estimating expression is obtained, determining a prediction gain of the FIR band elimination filter at the determined frequency, and determining that the input signal is a tone signal if a value of the determined prediction gain exceeds a preset threshold value.

Abstract: A method and apparatus logs outgoing phone symbols dialed from an extension. To log the phone numbers, a switching network is coupled to the phone lines and passes a Dual Tone Multiple Frequency signal from the extension to a CODEC. The CODEC converts the analog signal it receives into a series of digital values that are passed to a digital signal processor. The digital signal processor decodes the series of digital values into a set of dialed-symbol values indicative of symbols dialed by the extension. The dialed-symbol values are packaged by a processing unit interface and transmitted to the processing unit where they are stored in a log database.

Abstract: A multifrequency detector, such as a DTMF detector, includes a Goertzel module detecting energies of a current frame of an incoming signal at nominal tone frequencies. A number of ratios are computed from the detected energies and supplied as an input to a multidimensional thresholding device such as a neural network. The neural network generates a decision level to be used in a subsequent frame decision. A frequency estimation module also receives the incoming signal and generates a number of frequency estimation indications to be used in the final determination of whether the incoming signal contains a valid multifrequency signal. A low-level decision module returns a frame decision result (D/N) for the current frame based on inputs from the Goertzel module and the decision level. A high-level decision module receives the frame decision result and information based on the frequency estimation indications.

Abstract: Apparatus and methods for adaptively, reliably, and accurately measuring the duration of an alerting or other signaling tone. A tone detector in accordance with the principles of the present invention accurately measures a duration of a tone burst (i.e., tone pulse) using a long frame length DFT and a short frame length DFT. Based on information obtained by the short frame length DFT, the long (i.e., standard) frame length DFT may be interrupted and reset to begin a new frame of data synchronized with the start of the next short frame corresponding to the processing by the short frame length DFT to minimize noise in the processing by the long frame length DFT and to greatly improve the resolution of the measurement of the duration of a particular tone to correspond to the lengths of the short frames used by the short frame length DFT.

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: An arithmetic processing section is designed to repeatedly execute product-sum arithmetic processing a number of times equal to the number of samples corresponding to each of the frequencies, in which a value obtained by subtracting a product-sum arithmetic value two sampling periods before from an input signal and a value obtained by multiplying a product-sum arithmetic value one sampling period before by a coefficient corresponding to a reference frequency contained in a DTMF signal are added. A comparator extracts an output value equal to or larger than a predetermined threshold value from the product-sum arithmetic values obtained by the arithmetic processing section. A matrix section determines the type of DTMF signal on the basis of at least two output values extracted by the comparator.

Abstract: A line card for interfacing with a plurality of subscriber lines includes a plurality of data processors and a tone detector. Each of the data processors is associated with one of the subscriber lines. The tone detector is adapted to detect one of a plurality of activation tones on a selected subscriber line. The plurality of activation tones include a first activation tone having an active portion and a silent portion. The active and silent portions repeat periodically at a first frequency having a first period. A second activation tone has a phase reversal portion repeating at a second frequency and having a second period. The tone detector is further adapted to sequence between the subscriber lines at a predetermined interval. The predetermined interval is based on the first and second periods. The tone detector is adapted to signal the data processor associated with the selected subscriber line in response to detecting one of the activation tones.

Abstract: Deactivating a switch in a handset when a user wishes to answer an incoming call or terminate a call. A sound card within a personal computer transmits a hook tone that is above the human hearing range to a transmitter section of the handset. When the switch is in the activated state, the handset re-transmits the hook tone back to the sound card which converts the hook tone to digital information so that the hook tone can be detected by software running in the personal computer. When the manual switch is deactivated, the handset ceases to re-transmit the hook tone back to the sound card. The software detects the absence of the hook tone to determine if the handset is answering the incoming call. In traditional telephony terms, when the manual switch is deactivated, this is the offhook condition. When the manual switch is activated, this is the onhook condition.

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

Abstract: A method and apparatus are described for using a series of signals that create an illusion of a continuous ascending or descending series of pitches as call waiting or call progress or process progress signals. In a preferred embodiment, a condition appropriate for representation by a call waiting or call progress or process progress signal is detected and, in response thereto, a series of signals is generated that creates an illusion of a continuous ascending or descending series of pitches. Preferably, the series of signals is Shepard's tones and the tones are generated by generating a plurality of tones, or partials, at octave intervals, amplitude filtering the partials to produce an amplitude envelope that peaks near the centermost partial or partials, and shifting the partials upwards (or downwards) through the octave in steps that are a fraction of an octave and preferably are a semitone.

Abstract: Computationally efficient DTMF detection methods and apparatus are presented that meet all of the ITU recommendations using the modified non-uniform DFT. The system of the present invention employs a high band filter block and two low band filter blocks to detect power at the 8 DTMF tones. The frame length of the high band filter blocks is one half the length of the low band filter blocks. The frame lengths are chosen to meet the ITU frequency selectivity requirements for all DTMF frequencies. The frames of the two low band filter blocks are staggered to produce outputs alternately, and are aligned with respect to the frame of the high band filter block to produce low band filter block outputs that coincided with the high band filter block outputs without the need for signal buffering. A system of power level tests are employed in conjunction with a system of timing tests to ensure that all ITU timing and frequency constraints are met.

Abstract: A signal detector includes a transform unit and a cross-frame energy level unit. The transform unit is adapted to receive at least a first and a second frame of time domain input samples. The transform unit generates at least a first frequency energy value for the first frame and a second frequency energy value for the second frame based on the time domain input samples. The cross-frame energy level unit is adapted to compare the first frequency energy value to the second frequency energy value to determine the presence of a first tone in the time domain input samples. A method for detecting a signal includes receiving at least a first and a second frame of time domain input samples. At least a first frequency energy value for the first frame and a second frequency energy value for the second frame are generated based on the time domain input samples. The first frequency energy value is compared to the second frequency energy value to determine the presence of a first tone in the time domain input samples.

Abstract: A communication terminal comprising a receiving path and a sending path linked to the communication line, the receiving path being connected to a system able to detect, during a communication, an alert signal (e.g., a CAS signal) sent by a station (e.g., the local telephone exchange station or central office) upon any new call or connection request for the terminal and able to allow reception by the terminal, e.g., of data related to each new caller, by interrupting temporarily the presently existing communication, the terminal including a detector (7) able to detect any activity or any signal transmission, and/or the absence of the same, in the sending path (3) of the terminal (1) and to deliver a corresponding information signal (IS) to the signal detection system (5), the latter adjusting its detection method or mode or selecting a corresponding detection subsystem accordingly.

Abstract: An apparatus and method are disclosed for providing backup power over communication wires from a central office of a service provider to a remote customer premise. In accordance with the invention, a high voltage direct current (HVDC) power signal and a digital data signal are combined and coupled to the communication wires at the central office. The combined signal is then transmitted along the communication wires to the remote customer premise. At the customer premise, the HVDC power signal is separated from the digital data signal. The HVDC power signal is then down converted into a low voltage direct current (LVDC) power signal that is coupled to premise communication wires at the remote customer premise. The premise communication wires them provide a path for the data signal and the LVDC power signal to the customer premise equipment (CPE). Thus, a reliable and safe source of backup power is provided for the CPE over existing communications wires.

Abstract: A signal detector includes a transform unit, a gain control unit, and an energy level threshold unit. The transform unit is adapted to receive a plurality of input samples and calculate a first plurality of delay values based on the input samples. Each delay value is based on at least one previous delay value and a current input sample. The transform unit is adapted to calculate a first energy value based on at least a subset of the first plurality of delay values. The gain control unit is adapted to determine if a selected delay value of the first plurality of delay values exceeds a predetermined threshold and scale the selected delay value, the at least one previous delay value used to calculate the selected delay value, and subsequent input samples received after the current input sample by a first amount in response to the selected delay value exceeding the predetermined threshold.

Abstract: An apparatus for determining energy threshold detection values for detecting at least one tone having a known frequency and duration in an input signal. The input signal is input over a period of time that is divided into frame portions including at least an initial frame portion and a last frame portion. An energy value is determined for the at least one tone during each frame portion. A set of control flag signals are set for the at least two frame portions based on the energy values being below a threshold value in previous frame portions and the presence of noise in previous frame portions. An offset into a data table is determined based on the control word, the offset being used to retrieve a scaling coefficient and an address of an energy value for the at least two frame portions from the data table.

Abstract: This invention allows enterprises to achieve specific objectives in the management and enforcement of policies related to the use of telecommunications services. It was conceived for use in connection with traditional telephone networks that carry voice, facsimile or voice-band-data (VBD) traffic, though it is not necessarily limited to such networks. It involves measurement of the properties of traffic on a communications channel, and the use of such knowledge in combination with various ancillary properties of telecommunications service usage to guide the conditional performance of prescribed actions based on user-defined policies. The measured traffic properties include classification of the type of traffic, where the set of possible classes include zero or more classes selected from a group of general categories comprising Voice, Facsimile, Voice-Band-Data, DTMF, Audible Network Signaling, Facsimile Handshaking, Voice-Band-Data Handshaking, Silence and Unknown.

Abstract: A ring back signal for a call between a calling party and a called party can be simulated. A ring back message associated with the call is received. The calling party is associated with a first network. The called party is associated with a second network. A prestored ring back signal is selected from a set of prestored ring back signals based on the ring back message and/or a called number for the call. The selected prestored ring back signal is associated with the second network and is different from a second prestored ring back signal associated with the first network. The prestored ring back signal is sent to the calling party.

Abstract: A method and system for facilitating the detection of DTMF tones is disclosed. The method is based on detecting two tones using a modified nonuniform discrete Fourier transform that includes a phase correction term for each DTMF tone and harmonic. The disclosed method is employed by a DTMF detector that includes a sampling module, a computation module, an analysis module, and a decode module. The sampling module samples an input signal from a communication network at a rate sufficient to avoid data loss. The sample signal is then placed through a modified DFT which is more precise than filters or analog devices, particularly those utilizing a Goertzel algorithm. The computation module implements a fast recursive algorithm for completing the necessary computations. The analysis module checks for the present of energy level peaks at the DTMF tones and their harmonics. Once a DTMF signal is verified to contain a DTMF tone, the decode module transmits the,number, letter, or symbol to an interface.

Abstract: A signal detector for detecting at least a first signal having a first frequency includes a matched transform unit and an energy level threshold 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 and a first matched filter coefficient. The sampling frequency is a non-integral multiple of the first frequency, and the first matched filter coefficient depends on the first frequency. 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 is provided. The method includes receiving at least a first frame of time domain input samples at a sampling frequency.

Abstract: A method for characterizing a dual frequency (DF) signal including the steps of sampling the signal at a sampling frequency vs so as to obtain a sequence of signal samples, and obtaining an &agr;-constant and a &bgr;-constant of the DF signal meeting a predetermined criterion.

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: A method and a communication device detect a service signal and include a converter having a first input which is connected to a communication channel for communicating with a network. An input device is connected to a second input of the converter for providing input signals to the converter. An echo canceller receives the input signals to form a replica of echo present in output signals from the converter for cancelling the echo and forming modified output signals. An output device is connected to an output of the echo canceller for receiving the modified output signals, and a service signal detector is connected to the output of the echo canceller.

Abstract: A telephone incoming signal discriminator constructed to include a first relay, a FSK detector, a DTMF detector, a pin detector, a tone amplifier and oscillation control, a FSK/DTMF decoder IC, a memory, a buzzer, a comparison/setting control IC, an auto answer machine, and a second relay, wherein when a telephone signal comes, it is detected by the FSK detector and the DTMF detector, and then decoded by the FSK/DTMF detector IC, and then compared with the set code by the comparison/setting control IC, so that the comparison/setting control IC drives the telephone to ring when matched, or switches on the second relay for enabling the incoming telephone signal to be shifted to the auto answer machine when not matched.

Abstract: A fire retardant, intumescent, curable composition for use in composite materials has as its principal ingredients a curable resin system and a fire retardant combination of a polyhydroxy compound, a polyphosphate, a nitrogen-containing compound and a polyacrylate monomer. Significant reduction of the flame spread index is achieved.

Abstract: An amplitude modulation detector use peak detection. A CAS (Customer premise equipment Alert Signal) detection apparatus and a caller information detection apparatus use the peak detection and methods for CAS and the caller information detection. The CAS detection apparatus includes a mixing unit, an amplitude modulation detection unit, and a frequency discriminating unit. The mixing unit mixes two or more frequency components of the input signal to generate an amplitude modulated signal including a carrier and an envelope. The amplitude modulation detection unit measures the envelope. Also, the frequency discriminating unit detects whether the frequency of the envelope is in a predetermined range to discriminate whether the CAS is present. Thus, the existence of the CAS can be detected through a single path by mixing a dual tone CAS signal, and can be accurately detected by discriminating the frequency the envelope.

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: A system and method for detecting and removing tones from an incoming communications channel that may also carry other signals such as, for example, voice is disclosed which includes pre-detecting tones in a communication signal, processing the communication signal to invalidate the tones in response to the tone pre-detection, forwarding the processed communication signal across a network, validating the tone and forwarding tone-on signals across the network in response to the validation.

Abstract: A signal acquisition device captures signals from a telecommunication line such as a local loop. The captured signals are spectrally analyzed using a signal-processing unit. The output of the signal-processing unit—in the form of a test spectrum—is provided to a signal identification system. The signal identification system comprises at least one of a plurality of spectra of known signals stored as templates. Using a matching algorithm, the spectrum of the test signal (unknown signal) is correlated with spectra of at least two known signals. The unknown signal is determined to be the same type as that of the known signal with whose spectrum the unknown signal produces the largest absolute correlation score. Alternatively, an unknown signals is determined to be that of a known signal if a correlation of both signals results in a score the absolute value of which is greater or equal to a predetermined threshold level.

Abstract: Signaling tone detection systems are presented that may allow for reductions in talk-off, cut-through, or both. In one general aspect, a detection system includes an outgoing signaling tone detector responsive to an output from a first station to a communication channel. An incoming signaling tone detector is responsive to an input to the first station from the communication channel. A sensitivity control input of the incoming signaling tone detector is responsive to a detection output of the outgoing signaling tone detector. This and other configurations may allow a system to detect tones more reliably, or they may allow a system with particular computational capabilities to detect more tones with a similar level of accuracy.

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: This invention intends to provide a tone signal detection circuit that accurately detects a tone signal regardless of a reception electric field strength. To accomplish this object, the tone signal detection circuit according to the invention is comprised of a first filter that extracts a signal of a specific frequency from an input signal, a second filter that excludes the signal of the specific frequency from the input signal and extracts signals of frequencies near the specific frequency, a subtractor that subtracts an output of the second filter from an output of the first filter, and a judgment circuit to judge whether the tone signal is present or not in the input signal on the basis of an output from the subtractor.

Abstract: The invention is to provide a DTMF decoder having a minimum power consumption. A signal inputted to a digital demodulator of the invention is respectively inputted to a bandpass filter for a DTMF signal of a low frequency band, a bandpass filter for a DTMF signal of a high frequency band, a bandpass filter for a DTMF signal of a middle frequency band, and levels of signals passed through respective filters are measured by a level measuring device for the DTMF signal of a low frequency band, a level measuring device for the DTMF signal of a high frequency band, and a level measuring device for the DTMF signal of a middle frequency band.

Abstract: Computationally efficient DTMF detection methods and apparatus are presented that meet all of the ITU recommendations using the modified non-uniform DFT. The system of the present invention employs a high band filter block and two low band filter blocks to detect power at the 8 DTMF tones. The frame length of the high band filter blocks is one half the length of the low band filter blocks. The frame lengths are chosen to meet the ITU frequency selectivity requirements for all DTMF frequencies. The frames of the two low band filter blocks are staggered to produce outputs alternately, and are aligned with respect to the frame of the high band filter block to produce low band filter block outputs that coincided with the high band filter block outputs without the need for signal buffering. A system of power level tests are employed in conjunction with a system of timing tests to ensure that all ITU timing and frequency constraints are met.

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: The apparatus of the invention (a) monitors a subscriber line for the presence of DTMF tones, (b) intercepts DTMF tones by transmitting a set of DTMF harmonics onto the subscriber line, (c) detects the intercepted DTMF tones and records them or the digits they represent, (d) analyzes the intercepted digits to determine whether a long distance number has been dialed, and (e) if a long distance call has been dialed, transmits onto the subscriber line a DTMF signal which includes the intercepted DTMF signal plus a service provider access code DTMF signal inserted before it. According to a presently preferred embodiment, the apparatus includes a voltage sensor which detects a drop in voltage whenever a phone connected to the same subscriber line as the apparatus goes off-hook. The voltage detector turns the apparatus “ON” when an off-hook condition is detected.

Abstract: A system suitable for encoding typographic characters into two digit base ten values and to decode such values to typographic characters are disclosed. The system maps typographic characters, such as letters in the English language and puctuation symbols into two decimal digit numeric codes. The mapped numeric codes allow all upper and lower case English letters to be identified by a unique two digit code, that may be encoded using conventional DTMF tones. The system similarly decodes two digit numeric codes, so encoded. The system optionally include a DTMF generator and decoder. Methods used by the system are also disclosed.

Abstract: Multiple characteristics of an signal are measured to determine the presence of an alert tone on an incoming signal to a customer premises equipment (CPE) in preparation for receipt of FSK modem signals. The apparatus, method, and article of manufacture discern the presence of an alert tone by measuring characteristics of the incoming signal. The alert tone is able to be discerned even under crosstalk conditions and over a wide dynamic range with the digital signal processing (DSP) method and apparatus described. Multiple characteristics of the signal are measured to determine the presence of the alert tone.

Abstract: Detection of alerting or other tone signals in a composite signal are reliably detected with an improved false tone detect suppression technique which employs the use of a moving window analysis on a subset of frequencies detected within an underlying speech signal performed during each of a plurality of data frames. The composite signal is transformed during each data frame using a discrete Fourier transform comprising the so-called Goertzel Algorithm. All of the Goertzels relating to the tone detection are analyzed during each data frame, but only a subset of the Goertzels relating to the sweeping harmonic analysis of the underlying speech signal are analyzed during any particular data frame.

Abstract: Computationally efficient DTMF detection methods and apparatus are presented that meet all of the ITU recommendations using the modified non-uniform DFT. The system of the present invention employs a high band filter block and two low band filter blocks to detect power at the 8 DTMF tones. The frame length of the high band filter blocks is one half the length of the low band filter blocks. The frame lengths are chosen to meet the ITU frequency selectivity requirements for all DTMF frequencies. The frames of the two low band filter blocks are staggered to produce outputs alternately, and are aligned with respect to the frame of the high band filter block to produce low band filter block outputs that coincided with the high band filter block outputs without the need for signal buffering. A system of power level tests are employed in conjunction with a system of timing tests to ensure that all ITU timing and frequency constraints are met.

Abstract: A telephone system including improved voicemail wherein a digital signal processor scans data to be recorded in a voicemail message to find DTMF tones or DTMF mimics in the voice data and removes them from the recording. In one embodiment, the DSP scans for DTMF tones or mimics in the stream of data to be recorded and removes them before recording the data. In another embodiment, the DSP scans for DTMF tones and mimics in the stream of data to be recorded, and marks the starting point and ending point in the stream where DTMF tones or mimics are found, records all the data and then goes back to the recording after it is finished and looks for the markers and removes all data between the markers.

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: A touch-tone receiver (TTR) simulator is disclosed to analyze DTMF signals and facilitate the investigation of call failure problems. The TTR simulator captures DTMF data received by a private branch exchange (PBX) switch and utilizes the instruction set of the TTR being simulated to process the received DTMF signals on the simulated TTR. Diagnostic tools allow step-by-step tracing and recording of the instructions performed by the simulator. The TTR simulator allows the underlying cause of a call failure problem due to DTMF signals to be identified. Results of digit interpretation can be compared to expected results.

Abstract: A telephone answering apparatus for detecting the source of a telephone tone signal includes a signal detector for detecting the telephone tone signal, a memory storage device for storing a message, and a controller for stopping playback of the message in response to the telephone tone signal wherein the controller determines whether the telephone tone signal is present while playback of the message is stopped. A timer is operatively connected to the signal detector to designate a period of time for the signal detector to detect for the presence of the telephone tone signal while playback of the message is stopped.

Abstract: A method of transmitting DTMF signals over a compressed computer network (24) comprises sending a packet containing a compressed DTMF signal followed by a confirmation packet. The confirmation packet preferably comprises an uncompressed DTMF signal which is transmitted on the same logical channel as the packets that represent voice signals. To detect the DTMF signal transmitted, a telephony Internet server (28) decompresses packets as they are received. If a packet appears to contain a compressed DTMF signal, the telephony Internet server looks for the presence of the confirmation packet before processing the previously received packet as a DTMF signal. In an alternative embodiment, the confirmation packet comprises a code that represents a DTMF signal. The packets that represent the voice signal and the code representing the DTMF signal are sent on separate virtual channels of the same logical channel.

Abstract: A communications device is presented including a DTMF detector for detecting a DTMF signal. When the DTMF signal is a Mode 2 Caller ID CAS, the first DTMF tone has a frequency of about 2130 Hz, and the second DTMF tone has a frequency of approximately 2750 Hz. An input signal includes signal energy within a first portion of the input signal frequency range which includes the first DTMF tone, signal energy within a second portion of the input signal frequency range which includes the second DTMF tone, and signal energy within a third portion of the input signal frequency range which excludes the first and second DTMF tones. The DTMF signal detector includes a first and second tone detection units, an extraneous signal detection unit, and detection logic. The first and second tone detection units receive the input signal and produce an output signal dependent upon the signal energy within the respective first and second portions of the input signal frequency range.