Abstract: A method for detecting the presence of single tone and dual tone signals compares a ratio r which equals the square of the maximum value of the received signal (A max) during a sampling period divided by a measure E of the energy to three different thresholds. If r is less than the first threshold (3) a single tone is indicated. If it is greater than the first but less than the second (5.2) a dual tone is indicated. When a single tone is indicated the received signal is subjected to a second order autoregressive process to determine the frequency of the single tone. If a dual tone is indicated the received signal is subjected to a fourth order autoregressive process to determine the frequencies of the dual tones.

Abstract: A digital line card is provided for use in an electronic messaging system for enabling the receipt of voice and text or image data over a single communications port. The digital line card includes a digital signal processing integrated circuit, a microprocessor and a random access memory component for storing coding schemes employed by the digital signal processing integrated circuit. The digital line card is programmed to detect the presence of dual-tone multifrequency command signals in the incoming data stream, and to switch between voice and data processing responsive to the command signals.

Abstract: An apparatus for interfacing an analog telephone in an ISDN terminal adapter is able to independently perform call set-up regardless of a personal computer's operation, while being provided with ISDN audio service via an existing analog telephone. The apparatus includes a combocodec for converting a digital audio signal from the co-processor into an analog audio signal to supply it to a telephone, and for digitizing an analog audio signal from the telephone to supply it to the co-processor; a ring generator for generating a ring signal under the control of the co-processor; and a DC-voltage converter for generating a telephone driving voltage. A subscriber line interfacing circuit (SLIC) is connected to a telephone, a DC-voltage converter, and a combocodec, for supplying the telephone driving voltage to the telephone, interfacing the audio signals between the telephone and combocodec, and sensing the office line to determine the telephone's hook state.

Abstract: Multifrequency signals are detected in a received signal by extracting filter coefficients from the received signal, generating line spectrum frequency (LSF) parameters from the filter coefficients, and processing the LSF parameters to identify multifrequency signals. The LSF parameters are first examined to see if the lowest frequency represented by the LSF parameters is below a predetermined frequency, e.g., 600 Hz, and if so it is determined that the signal is not a multifrequency signal. The parameters are next examined to see if there are exactly two sharp frequency spectrum peaks, with a sharp peak being defined by two consecutive LSF frequencies separated by less than some predetermined frequency range, e.g., 60 Hz. Assuming there are two peaks, the locations of the peaks are examined to see if they correspond to the possible tone pairs, thereby identifying a particular multifrequency tone.

Abstract: A technique for improved DTMF detection utilizes a speech detector, either alone or in combination with other information from a voice processing arrangement, to adjust the sensitivity of the DTMF detector. The DTMF detector is turned completely off when the voice processing application is in the record mode, and when speech is detected.

Abstract: A DTMF signal receiving circuit which is capable of freely selecting a frequency of a received dial tone signal. The DTMF signal receiving circuit receives a DTMF signal, decodes the DTMF signal, and outputs the signal as the decoding result. The DTMF signal receiving circuit comprises a dial tone signal detecting circuit for freely selecting a frequency of a dial tone signal which is the object of detection in accordance with a supplied selection signal, and a judging circuit for judging whether or not the signal as the result of detection of the DTMF signal is output on the basis of the output of the dial tone signal detecting circuit.

Abstract: The present invention provides a method and apparatus for detecting control signal information for an element of a communication system. The control signal information is included in one or more segments of a signal communicated over a communication system channel. The invention provides for the application of a plurality of tapers to a segment of a communicated signal; the transformation of a tapered segment; the determination of a similarity score based on a transform of a tapered segment and a model of a control signal; the identification of control signal information based on a similarity score; and the creation of an indicator signal representative of the identified control signal information to the communication system element. The control signal information may comprise a dual-tone multi-frequency signal. The tapers may comprise a discrete prolate spheroidal sequence. A similarity score may be determined based on a ratio of energy distributions.

Abstract: A method of improving the sensitivity and speech immunity of a receiver in conjunction with DTMF-reception is disclosed. The number of zero-crossings of the input signal are counted during one of a number of measuring intervals in real time at frequencies which occur in the low frequency group and the high frequency group of a DTMF-signal. At the end of each of the measuring intervals, the number of zero-crossings in a current measuring interval is compared for each frequency group, with a corresponding number of zero crossing in a number of nearest preceding measuring intervals, and the magnitude of any difference is established. The input signal is treated as a DTMF-signal when the difference is at most equal to a permitted limit value.

Abstract: A method and system for efficiently recognizing the last digit of a computer-dialed DTMF telephone number. The actual gaps between a number of first-dialed successive digits are compared with a standard gap exhibited during computer dialing to determine whether the dialing in progress is manual or automatic. As dialing proceeds, the absence of a digit for a preset time indicates that dialing has been completed. The preset time is set to a small value if it is determined that computer dialing is in progress.

Abstract: A substantially-universal detector (FIG. 2) of far-end call disconnect-indicative tones detects the foreseeable forms of tone-based signalling of remote-end call disconnect that are likely to be employed anywhere in the world, without reconfiguration or reprogramming for different tones or countries. Implemented in the digital signal processor (DSP 30) of port circuits (14, 20) of switching systems (11) or adjunct processors (12), the detector determines parameters (204) of signals carried by the call to the near end and uses them, along with already-present linear predictive coding (LPC) predictor coefficients (202) and indications of energy (203) in the signals, in a multivariate classification (230) of call progress tones from other tones. When presence of any call progress tones is thus detected substantially without interruption for a predetermined minimum time in the received signals, the call is considered (240) to have been disconnected at the far end.

Abstract: Call setup time is reduced by automatically (1) identifying the type of signaling used by a caller to communicate with a central office, and (2) providing an indication of the signaling type to telephone switches or databases that will participate in routing and processing the telephone call. Dual Tone Multifrequency (DTMF) detectors located at a central office of a local exchange carrier detect whether a caller is using DTMF signaling. The local central office includes this information in a signaling message provided, for example, to interexchange carriers and other service providers which will use DTMF signaling during and after call setup. In this manner, the need to query the caller for this information is eliminated.

Abstract: A dual tone detector (100) for a single dual tone, a dual tone multi-frequency (DTMF), or similar system processes an input signal through both bandpass (103) and band reject (104) tone detectors. If both the bandpass (103) and band reject (104) tone detectors detect a tone, then the dual tone detector (100) provides a tone detect output signal. If only the bandpass tone detector (103), which is susceptible to false tones, detects a tone, then a voice input signal is muted and the tone detector (100) activates the tone detect output signal only if both the bandpass (103) and band reject (104) tone detectors subsequently detect a tone. In one embodiment, a dual bandpass/band reject tone detector (120) processes the input signal through shared front-end band reject filters (121, 122), limiters (124), resonators (127, 128), and a processing section (130) in order to save circuit area. Limiter and peak detector functions are also implemented in shared circuitry to further reduce circuit area.

Abstract: In a preferred embodiment, a method of automating configuration of a voice processing system including automating telephone tone parameter determination, including the automated functions of: generating a first telephone line tone; scanning the first telephone line tone for frequency parameters and cadence parameters; arranging the frequency and cadence parameters in a tone definition block structure; and storing the tone definition block structure into memory of the voice processing system for future use in recognizing the first telephone line tone.

Abstract: A method of dual-tone multifrequency (DTMF) detection which decimates and adaptively filters an input signal is provided to efficiently detect a presence of a DTMF signal. The input signal is provided to a half-band filter (14) to be decimated in frequency in accordance with Nyquist's theory. A decimated input signal is subsequently processed to form a low frequency component signal and a high frequency component signal. The low frequency component signal is again decimated by a decimator (24). The decimated low frequency component signal and the high frequency component signal are each filtered by an adaptive fir filter (22, 26) to provide a first and a second frequency parameter and a first and a second gain factor, respectively. The first and second frequency parameters and the first and second gain factors are then tested by a tone identifier (28) to determine if the input signal includes a valid DTMF signal.

Abstract: A method and apparatus for detecting and classifying signals that are the additive combination of a few constant-amplitude sinusoidal components, herein called N-tones. The attributes of this method and apparatus include provision of superior classification performance with an algorithm of low computational complexity. The method includes filtering to remove extraneous signal components, separation of the incoming signal into one or more output streams and segmenting these output streams into blocks of successive data samples. The magnitude of the data within each block is estimated along with the frequencies of the dominant spectral components. The frequency estimates are then used as part of the configuration process of a set of notch filters for removal of the identified dominant spectral components. The newly-configured notch filters are then applied to the same data blocks and the magnitudes of their outputs are estimated.

Abstract: A DTMF tone is detected through the tracking of two tunable filters HAVING coefficients within so-called tunnels each limited by thresholds derived from the tone frequency components to be detected. In and out-band energies E1(n) and E2(n) are used to further validate tone detection.

Abstract: A dialing receiver (1) for determining multifrequency dialing signals on an incoming signal in a telecommunication switching system, including a sampling circuit (4) for taking N values of the incoming signal at a given sampling rate, where N is a positive integer; a zero value generator circuit (6) for supplementing at the given sampling rate the N samples with M successive zero values so as to yield N+M values, where M is a positive integer; a discrete Fourier transformation circuit (7) for performing a discrete Fourier transform (DFT) of said N+M values in accordance with the Goertzel algorithm; and a result evaluating circuit (8) for directly evaluating the results of the DFT processing of the N+M values without interpolation so as to determine the identity of the multifrequency dialing signals.

Abstract: A telecommunication system (10) having a multiport receiving switch (12) with a central control circuit (14) for distributing information received over a multichannel link (28) from a multiport sending switch (30) to at least one of a plurality of various applications in the telecommunication system (10) with a data delay buffer (54) for temporarily delaying the sending of data transmitted across the multichannel link (28) to a peripheral circuit (26) for a predetermined interval in response to the seizing of a channel at the receiving switch (12).

Abstract: A method of operating a digital signal processor to detect DTMF tones in a digital voice telephone system in which the digitally encoded signals appearing on the telephone channel are decimated to compress the spectrum to be monitored for the appearance of call signalling tones. The signals received in a decimated block are "correlated" or convolved with one another on a forward and backward time-shifted basis and each forward and backward correlation product is summed to form the elements of a 5.times.5 modified covariance matrix. The modified covariance matrix exhibits the desirable property that its eigenvectors will be symmetric. Since all eigenvectors of the modified covariance matrix are orthogonal and the eigenvectors associated with the signal span the signal subspace, the signal subspace is orthogonal to the eigenvector associated with the noise. The dot product of the noise eigenvector with the signal subspace is set to zero.

Abstract: A method for monitoring a network communications channel to detect specific DTMF triggers transmitted by a network user during either a pre-answer or a post-answer period of a call supported by the channel, and, in response to the detected DTMF triggers, controllably prohibiting the propagation of subsequent DTMF signals transmitted over the channel by the network user. Specifically, possible disruption of a communication between the network user and other parties caused by transmission of DTMF signals is eliminated by advantageously transmitting the DTMF triggers during the pre-answer period of a call. Furthermore, another deficiency of prior network-based arrangements for restricting the propagation of DTMF signals is overcome, as the invention may be practiced without the introduction of any significant propagation delay to a network.

Abstract: A robust tone detector is realized by applying a single taper, which provides a relatively narrow bandwidth filter, to a received signal and, then, performing a Discrete Fourier Transform of the tapered signal. The result of the Fourier transform is used to obtain an estimate of energy in the frequency domain of the expected tone. A prescribed selection algorithm based on the relationship of the received signal energy in the time domain and the energy estimate in the frequency domain is used to determine whether a valid tone has been received. Robustness of the tone detector is improved by performing a plurality of Discrete Fourier Transforms of the single tapered version of the received signal at a corresponding plurality of frequencies relative to the nominal frequency of an expected one or more tones. A further improvement in the tone detector is obtained by the dynamically adjusting tone acceptance thresholds based on a measure of channel impairments.

Abstract: A data processor comprises a multifrequency receiver formed together with a central processor on a semiconductor substrate. The multifrequency receiver produces digital data for identifying a tone wave included in a multifrequency analog signal or produces an identification result in accordance with the condition or signal issued by the central processor. The multifrequency receiver is thereby operative to deal with tone waves which are flexible in type and input analog signals which are flexible in their frequency band, and has increased latitude of choice for the operational characteristics and function such as the number of sampling periods of input analog signals and the discrimination accuracy.

Abstract: Dual tone multifrequency ("DTMF") signal pulses are detected and identified by subjecting the signal being analyzed to complex bandpass filtering for each of the two DTMF frequency bands. The envelope of the outputs of each of these filters are determined and subjected to a succession of different tests including a ripple or smoothness test to ensure adequate smoothness, a ratio test to ensure the occurrence of a step function, a twist test to ensure the proper amplitude ratio between the two bands, and a minimum energy test to ensure that the signal has sufficient energy. If the signal passes all of the detection tests, then the actual DTMF signal is identified by using the real and imaginary parts of each complex bandpass filter output to compute an associated complex phase angle, and comparing that phase angle to the corresponding phase angles for valid DTMF tones.

Abstract: A multi-frequency signal receiver, and in particular a push-button signal receiver, is provided having a detector circuit and an amplitude variation supervisory circuit. The detector circuit has a group of band pass filters, each having a pass band corresponding to each elemental signal in the multi-frequency signal. The detector circuit also has a logic circuit for receiving each output from the band pass filters and outputting detected data of the multi-frequency signal. The amplitude variation supervisory circuit monitors the amplitude of an input signal for a predetermined duration and detects and holds the maximum value of the monitored amplitude. Then, the amplitude variation supervisory circuit detects when the amplitude of the input signal exceeds the maximum amplitude value to determine if the input signal is not the multi-frequency signal.

Abstract: A method and device for recognizing a signature of dialing pulse present in a communication signal isolate from the latter signal the signature. The so isolated signature is correlated with a statistic model obtained from a large number of dialing pulse signatures to determine whether the isolated signature corresponds to a dialing pulse. During this correlation, a first complex function representative of the isolated signature is calculated and correlated with a second complex function representative of the statistic model. The result of the correlation is normalized and whether the isolated signature is a signature of dialing pulse is decided in function of this normalization. The method and device can be used to convert into a tone frequency signal a series of dialing pulse signatures present in the communication signal and corresponding to a dialed digit.

Abstract: A data processor comprises a multifrequency receiver formed together with a central processor on a semiconductor substrate. The multifrequency receiver produces digital data for identifying a tone wave included in a multifrequency analog signal or produces an identification result in accordance with the condition of signal issued by the central processor. The multifrequency receiver is thereby operative to deal with tone waves which are flexible in type and input analog signals which are flexible in their frequency band, and has increased latitude of choice for the operational characteristics and function such as the number of sampling periods of input analog signals and the discrimination accuracy.

Abstract: A DTMF receiver for a push-button telephone, a facsimile apparatus or the like is disclosed. The DTMF receiver comprises frequency shift delay detection units for lower and higher groups of frequencies. Each of said frequency shift delay detection units comprises: a circuit for generating a first signal and second signal having a frequency obtained by subtracting the reference carrier frequency from the frequency of the corresponding frequency group, the signal having a phase difference of .pi./2 with respect to said first signal; another circuit for generating a third signal and fourth signal which are different in phase from the first and second signals, respectively; a vector calculation circuit in which the first and second signals are supplied to one input port, and the third and fourth signals to the other input port; and a detection circuit for detecting a phase difference between the outputs of the vector calculation circuit.

Abstract: The detection of DTMF tones is improved in a three-step process: first testing even-numbered samples; then testing odd-numbered samples, and finally testing for tone quality (time interval and frequency stability).

Abstract: Instead of setting the type of a dial signal for a central office line connected to a private branch exchange to either a DTMF signal or a pulsed signal externally of the private branch exchange, the line is acquired and a DTMF signal is transmitted from the private branch exchange to the line so that the line is recognized as a dial line for the DTMF signal when a dial tone coming from the line disappears but as a dial line for the pulsed signal when the dial tone does not disappear. Results of recognition are set in the private branch exchange and the type of the dial signal for the line is set automatically in accordance with the results.

Abstract: In a telephone-call distributor of the present invention, a dial data signal to be transmitted is generated by a control unit (1301, 2301, 3301) and DTMF signal generator (1328, 3328) in accordance with the dial data given to the control unit through a DTMF signal receiver (1327, 2323, 3327).

Abstract: A circuit is described for recognition of two-tone compound signals of two frequency ranges (F1 to F4, F5 to F8) in telephone installations with a limited transmission band width. Band pass filters (11, 12) whose output signals are added up and weighted individually are provided in a number corresponding to the number of possible single tones. The weighted output signals are each compared with the output signal sum of one of two frequency ranges (F1 to F4, F5 to F8 ) in order to signal a valid single tone. To increase the certainty of speech, another summand (Su, So) that is derived from a summation of the output signals of at least two other band pass filters (13) whose mid-band frequencies (F9 to F11) are outside the two frequency ranges (F1 to F4, F5 to F8) is also sent to the summation circuit.

Abstract: A specialized tone receiver is capable of detecting tones on many different digital signal channels simultaneously. A single memory is used to buffer incoming digital signals. Independent write and read sequencers write samples into and read samples from the buffer memory, respectively. The write sequencer writes all samples corresponding to a given sample time at essentially the same time, while the read sequencer reads out all of the samples corresponding to a given channel of interest in reverse sequential chronological order (i.e., in the opposite order from the order the samples were written) beginning with the most current sample. A priority structure controls access to the buffer memory, with the read sequencer being granted a higher access priority than the write sequencer.

Abstract: A tone detector comprising a circuit for detecting multi-frequency dialing (DTMF) signals applied to an input terminal and for generating a "DTMF present" indicating signal, and a circuit for detecting the presence of supervisory signals applied to the input terminal and for generating a "supervisory signal present" indicating signal. The dialing tones are converted to digital value signals and are preferably stored in a shift register. The digital value signals and the supervisory signals are applied in serial form to an output terminal. The "DTMF present" indicating signal is applied to a "DTMF present" terminal. Accordingly the presence of the "DTMF present" indicating signal can be monitored and thereby indicate whether the signal present on the output terminal is a digital value signal or a supervisory tone present indicating signal.

Abstract: A dual tone multi-frequency (DTMF) receiver for use in detecting digitally transmitted signals in the telephone industry. The receiver derives linear predictive coefficients for the digital signals in the data frame. This information is used to compute frequency response magnitudes at the DTMF frequencies. A plurality of magnitude comparisons are then performed to verify the presence of true DTMF signals and concurrently the frequency of these signals is obtained.

Abstract: The invention provides a circuit and method for the time-sharing of a DTMF tone receiver. A DTMF receiver has its input terminal connected to a common output terminal of a pair of transmission gates, each gate having an input terminal connected to a respective source of DTMF signals. A control circuit provides switching signals to the transmission gates to cause their input terminals to be connected alternately to the input terminal of the receiver at a predetermined rate until the receiver detects a tone signal on at least one of the input terminals of the gates. The control circuit includes circuitry responsive to the initial tone detection for inhibiting the further generation of switching signals until the tone detection by the receiver has been completed.

Abstract: The DTMF receiver sense and control arrangement collects and stores multiple customer originated data for determination of customer identification, validity and billing purposes. This arrangement is part of a telecommunications switching office and monitors up to 24 DTMF receivers (channels) to determine whether each channel contains valid data. This data is stored in temporary storage for subsequent transmission to a processor of the switching office. Each of the DTMF receivers asynchronously presents data for collection by this arrangement. This arrangement provides the proper timing required to operate up to 24 receivers to obtain their data, while it is stable at the receiver. Once a receiver transmits data, this arrangement then synchronizes its operation to that receiver so that, sequential monitoring of each of the 24 channels is guaranteed and no loss of valid data will result. In addition, each DTMF receiver may be enabled selectively for special monitoring.