Abstract: The present invention relates to a method of detecting call progress tones specified in a tone plan, comprised of calculating a power spectrum of a segment of an input signal containing a call progress tone, discriminating, based on the power spectrum, likely frequencies of the call progress tone, determining likely tone plan frequency bands based on between one and three of the frequencies, filtering the input signal in the frequency bands and extracting quadrature components of the input signal thereby, calculating three spectral moments of the input signal from the quadrature components for the frequency bands, and verifying at least one frequency of a call progress tone contained in the input signal based on the spectral moments.

Abstract: A DTMF digit detecting method and apparatus includes signal state identifier (32) for identifying whether the received signal is in a DTMF-digit-detect state, a no-detect high-energy state, or a no-detect low-energy state, digit candidate identification processor (34) for identifying a digit candidate when the presence of a state other than the no-detect low-energy state is detected following a detection of the presence of the no-detect low-energy state for a first predetermined period of time, digit identifier (32) for identifying a DTMF digit corresponding to a sample group in a DTMF-digit-detect state, and valid digit identifier (34) for identifying a valid DTMF digit when at least a first predetermined number of sample groups are all in the DTMF-digit-detect state or in an allowable combination of states.

Abstract: A method for detecting the presence of voice, 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. If it is greater than the second, the received signal level is compared to the third threshold (-43 dB) and receipt of a voice signal is indicated if the level of the received signal exceeds this threshold.

Abstract: A method and apparatus for detecting a dual tone alerting signal in the presence of speech for the purpose of initiating transfer of special service information on a telephone line is described. The apparatus includes two channels for separately detecting each tone. Each channel includes means for comparing the signaling energy around one of the tones with the energy in a selected weighted guard band portion of the voiceband. Based on this comparison, a determination is made whether a tone is or is not present. A pulse signal formed from the coincidences of tone detection in each channel is used by timing circuitry to determine whether the dual tone alerting signal is actually present or whether speech energy caused both tones to be erroneously detected (talkoff). Characteristics of this pulse signal are analyzed to determine whether an alerting signal is present.

Abstract: A computer scans the voice messages for phrases that will be detected as DTMF digits and creates a record of where, when and for how long the possible problem maybe occurring. This allows prerecorded or synthesized messages from a Voice Response Announcement System to be checked for error causing DTMF digits prior to being placed into operation. The complete system consists of a computer containing the detection unit, a disk storage unit and scanning program. The Detection unit is placed within the computer and connects the system to the Central Office Switching Network for access to the Voice Response Announcement System.

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 sensor circuit for telephone line includes a line current detecting circuit (52, 54) which generates a detection signal in response to a line current flowing in a telephone line (20, 22). The detection signal is applied to a first amplifier (56), and the detection signal as amplified is not only further amplified by a second amplifier (57) but also applied to a tone deriving circuit (60) and a CI detecting circuit (61) via a coupling capacitor (59). The detection signal as amplified twice is applied to a comparing circuit (58) which compares the detection signal from the second amplifier with a first reference voltage (V1) and a second reference voltage (V2), so that a line current supervisory signal is outputted from the comparing circuit. The tone deriving circuit includes a band-pass filter and derives a tone signal from the detection signal from the first amplifier. The CI detecting circuit detects a CI (calling tone) on the basis of the detection signal from the first amplifier.

Abstract: When there is an incoming call to a digital line and the digital line is to be connected to a digital terminal, a CPU connects the line and the terminal directly. When the digital line is to be connected to an analog individual line telephone or the like, the line and the terminal are connected via a level controller. The level controller shifts, to an appropriate level, the level of a voice signal represented by data received from the digital line, and the analog individual line telephone or the like connected to the extension receives the voice signal shifted to the appropriate level.

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: 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: Voice detector for detecting whether a telephone signal has been produced by a voice. The voice detector obtains, on a per frame basis, measures of the following quantities relating to the telephone signal: total energy; energy and frequency of two largest energy peaks in a frequency spectrum; and signal-to-noise ratio (SNR). If the measure of total energy exceeds a predetermined threshold, the voice detector increments running sums of the following measures: total energy; frequency of the largest peak in the frequency spectrum; and SNR. Until a predetermined number of frames, referred to as a window, has been reached, for each frame, the voice detector determines whether the telephone signal was produced by ringing (incrementing a ring count if it was) and whether there is a local energy maximum (incrementing a local energy maximum count if there was).

Abstract: A vocal frequency suppression apparatus for suppressing selected portions of a vocal signal to prevent inadvertent control of components controlled by dual tone multi-frequency ("DTMF") codes. The vocal frequency suppression apparatus includes a DTMF code generator having a plurality of user-selectable switches. The apparatus further produces a vocal signal which may contain vocal frequencies which correspond to at least one frequency of at least one of the DTMF codes. The apparatus includes a device for suppressing one or more of the vocal frequencies which correspond to frequencies found in the DTMF codes to prevent inadvertent control of any DTMF controlled components by the vocal signal. The suppression device is operably located between the producing device and the DTMF generator.

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 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 process for determining the presence of either speech or one of a plurality of expected single-frequency signals on a line includes the steps of measuring the total signal energy on the line; measuring the signal energy present in each one of a plurality of selected separate frequency bands and identifying the two frequency bands having the highest signal energies; determining whether the highest signal energy exceeds a first selected threshold value; determining whether the highest signal energy exceeds the second highest signal energy by greater than a second selected threshold value; determining the amount of out-of-band signal energy; and determining whether the highest signal energy exceeds the out-of-band signal energy by greater than a third selected threshold value.

Abstract: A method for real-time recognition of speech and call-progression tone energy includes the steps of digitizing an analog signal present on a signal line, correlating N neighboring portions of the digitized signal, performing FFT analysis on the digitized signal, identifying the three largest frequency-domain maxima, determining whether the two largest maxima are above a threshold frequency, and determining whether the ratio of the largest to the third largest maxima exceeds a predetermined value. According to the present invention, the steps of the method may be performed in real time using fixed-point hardware by approximating the correlation and FFT functions.

Abstract: A method of processing a signal having characteristics and received from a telephone line is presented. The method includes defining a frame by measuring a plurality of samples from the signal over a predetermined period. Additionally, linear prediction coding coefficients of a selected group from the plurality of samples are determined. Further, the variance of the linear prediction coding coefficients are determined and the variances compared to a reference variance. A heuristic rule is applied to a selected characteristic of the signal to determine if the signal comprises a voice signal.

Abstract: An enhanced telephony call waiting feature is provided wherein identifying information related to a third party wishing to converse with a first party already engaged in a conversation with a second party is spontaneously provided to the first party. The method comprises the steps of the local office sending a call waiting tone having predetermined characteristics to the first party and its apparatus responding thereto by muting its associated handset for a predetermined interval of time. The local office then transmits the identification data relating to the third party and the first party apparatus receives and displays to the first party the identification information related to the third party thereby allowing the first party to either accept or reject the waiting call in the conventional manner but also based on the displayed information.

Abstract: Method and apparatus allows accurate detection of voice presence on a digitized communication line even in the presence of tone signals. The method includes analyzing digitized communication input signals by current blocks of 20ms, to define the stationary or non stationary state of any current block. Then an analysis on the states of the M last 20ms blocks allows the final decision on voice presence.

Abstract: Voice signal information in a telephone-type signal is detected by subjecting the signal to several tests such as a minimum energy test, an amplitude ratio test, and a sequencing test which ensures that the other tests have been satisfied for a sufficient length of time and/or sufficiently frequently over a predetermined time interval. A voice processing system such as a voice mail system may use the detection of voice as above to initiate the transmission of an announcement or message during an automatically placed telephone call.

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: The invention is an adaptive method and apparatus for telephone call reorigination (i.e., the placement of successive calls without extended re-dialing). It allows shorter, uniform DTMF reorigination requests or commands to be recognized and responded to during certain stages of a call while preserving a filtering effect to avoid "talk off" reorigination during the call's talking stage. In the initial stage of a call, prior to verifying the caller's authority to place the call, a first mode of request detection, responsive to short duration tones is used. During call setup and prior to answer by a called party, a second mode of detection is used which is also responsive to short duration tones. In the talking stage, another mode of detection is used to avoid inadvertent reoriginations due to spurious tones. In one aspect, a dial tone is automatically returned to the caller upon called party disconnect.

Abstract: Apparatus for detecting and identifying DTMF signals in connection with a voice store and forward equipment (VSF) and for preventing talk-off, whether generated by the VSF or by a user of the VSF.

Abstract: A voice mail system includes method and apparatus for muting a previously recorded audio signal upon detection of a DTMF signal to differentiate between recorded DTMF signals and valid DTMF commands. A DTMF signal detected after muting is recognized as an invalid command.

Abstract: A signal is classified as one among a plurality of classifications by employing the autocorrelation of a complex low-pass version of the signal, i.e., the complex autocorrelation. The normalized magnitude of the complex autocorrelation obtained at a prescribed delay interval, i.e., "lag", is compared to predetermined threshold values to classify the signal as having one of a plurality of baud rates.

Abstract: A signal is classified as being one among a plurality of classifications by employing a prescribed relationship between absolute moments of a complex low-pass version of the signal. Specifically, the prescribed relationship is related to the second order moment of the magnitude of the complex low-pass version being normalized by the first order moment squared. This results in a so-called normalized variance which is compared to predetermined threshold values to classify the signal as having one of a plurality of modulation schemes, e.g., FSK, PSK or QAM.In another embodiment, a signal is classified as being speech or voiceband data. This is achieved by employing a phase relationship, i.e., the sign, of the autocorrelation of a complex low-pass version of the signal and the normalized variance. If the autocorrelation has a prescribed phase or the normalized variance is greater than a predetermined value the signal is speech, otherwise it is voiceband data.

Abstract: This invention enables voice energy to be distinguished from energy due to other sources such as telephone call progress signals. A portion of the audio spectrum is divided into a high and into a low frequency band and the energy content of these bands is examined. The audio energy of a signal is passed through a set of filters and compared. A frequency boundary crossing of an input signal subsequent to filtering is used to signify the receipt of a voice signal. By operating in this manner, voice, whose predominant frequency switches in a random fashion from being greater than to less than a cutoff frequency, can be distinguished from other signals either below or above the cutoff frequencies of the filters. The detection of voice energy is not begun until a predetermined threshold of energy has been received for a specified period of time. This specified period of time need not be continuous after a ringback signal is received.

Abstract: A device for detecting voice signals in the presence of supervisory signals on a number of telephone lines so as to determine when machine-placed telephone calls have been answered. The device comprises a zero crossing detector for each telephone line monitored to determine the zero voltage crossings in the voltage of an incoming telephone signal, a latch associated with each detector for storing the occurrences of each zero voltage crossing detected and a microcomputer for processing the frequency-related information of the incoming telephone signals according to a voice detection algorithm. The voice detection algorithm comprises timer interrupt and analysis routines that direct the microcomputer to count the number of occurrences of different wavelengths of the waveforms composing an incoming telephone signal in determining the condition of response on a respective telephone line.

Abstract: A circuit for surge voltage protection of therefor a telephone station has first and second input terminals for receiving a DC supply voltage via a two-wire subscriber line. Both terminals are shunted via a varistor. In parallel with the varistor is an element for protecting the circuit against polarity reversals. This element has two outputs, one of them carries the positive potential of the DC supply voltage and both of them are connected with respective terminals of the actual station circuit. A V-MOS or bipolar tranistor is arranged between the one output and the associated station circuit terminal. This transistor belongs to a current limiting circuit and serves also as a dialswitch-pulsing contact. The transistor circuit contains two further transistors and a number of dimensioning resistors. The positive output of the protection element is connected to the keyboard-sided input of the transistor circuit via a series network formed by a reverse Zener-diode and a resistor.

Abstract: A novel apparatus and method for electronically determining whether audio signals which are present in an electrical audio device (for example, a telephone) are voice signals or, on the other hand, some type of supervisory or system-generated signals. Audio signal lines are connected to an audio detector and a digitizer. The audio detector provides an output which indicates the presence of an audio signal. The digitizer transforms any audio signal into a series of high and low level signals in some manner. The outputs from the audio detector and the digitizer are then provided to a central processing unit which is used to analyze the data. If an audio signal is detected and the digitized audio signal is determined to have a regular periodic pattern, it is presumed that the audio signal is some type of system-generated supervisory tone. If, on the other hand, the digitized audio signal does not have a regular periodic pattern, it is presumed that the audio signal is a voice signal.

Abstract: A ring generator capable of supplying a plurality of predeterminedly selected distinct voltages each having a predetermined high amplitude and a predetermined frequency to a telephone line comprises a programmable computer having a low amplitude version of the plurality of voltages stored therein in digital form, the computer being responsive to predetermined control signals to select a desired one of the low amplitude version of the plurality of voltages stored therein, a first circuit arrangement coupled to the computer to convert the select one of the low amplitude version of the plurality of voltages to an analog version thereof and to increase the analog version to the predetermined high amplitude prior to coupling to the telephone line and a second circuit arrangement coupled to the first circuit arrangement, the telephone line and the computer to monitor the selected one of the plurality of voltage coupled from the first circuit to the telephone line to detect the operating condition of the ring genera