Abstract: A signal discrimination circuit judges whether an input signal contains a control signal or not, the control signal having a specific frequency and a specific level for a specific time duration. The signal discrimination circuit includes a component power detection device for detecting the power of a component which is in the input signal and having the specific frequency and a level judging device for determining whether the power of the component is equal to or greater than a power reference value. Finally, a control signal judging device is included for determining that the input signal includes the control signal, when the level judging device judges that the power of the component is equal to or greater than the power reference value, continuously for the duration of a reference time.

Abstract: An emergency locator light can be located based on an optimum viewing of the light, rather than being limited by hard wiring limitations. The apparatus responds to dialing of a predetermined emergency telephone number, such as 911. A light switching mechanism is provided for activating the emergency light upon receipt of a signal code from a signal code generator. The signal code is transmitted when the system detects the dialing of a predetermined emergency number. The apparatus detects the transition from either on-hook voltage to off-hook voltage or off-hook voltage to on-hook voltage, or both, in order to set and reset the dialing monitor unit. The apparatus, when set, detects the dialing of the emergency phone number. Upon detection of the emergency number a signal code is transmitted to the light switching member. The signal can be transmitted by a wireless transmitter, such an RF or microwave frequency transmitted.

Abstract: A three-way call detection and response system comprising, in accordance with a preferred embodiment, a three-way call detector coupled non-intrusively, by a bridge repeater, to a communication path carrying digital signals between originator and recipient end office telecommunication switches. The three-way call detector includes an interface and a digital signal processor electrically connected to the bridge repeater for receipt of digital signals from the communication path. The three-way call detector also includes a local controller which interacts with the interface, a digital signal processor, and a remote controller. The remote controller executes a plurality of software programs which control operation of the system. In accordance with a preferred method, the three-way call detection and response system monitors the communication path for indicia representative of a three-way call signature and, hence, an attempted three-way call placement.

Abstract: An ADSL receiver (200) receives an upstream modified ADSL signal and an ISDN signal from a remote terminal (32) on a twisted-pair copper wire (18). An ADSL transmitter (100) of the remote terminal (32) transmits the ADSL signal in a frequency range above an ISDN frequency range so that the ADSL signal does not overlap the frequency range of the ISDN signal. In one embodiment, the ADSL receiver (200) includes a band pass filter (201), an analog-to-digital converter (203), a decimator (205), a fast Fourier transform (210), and a digital signal processor (212). The decimator (205) converts the ADSL signal back to base band, thus allowing an ADSL signal source to simultaneously utilize the telephone line with an ISDN signal source, without significantly reducing ADSL throughput.

Abstract: An automatic call distributor (10) having a multiport switch (12) controlled by a central control processing unit (14) and an associated memory (16) for receipt of audio voice energy from answered telephonic calls through an external telephonic public switching network (22) to selectively connect the answered calls with internal telephonic units (18) coupled with the multiport switch (12) provided with a digital signal processing circuit card (30) for determining the presence of an answering machine (24) by running a pause timer and a delay timer which disables execution of the pause timer to establish a first minimum time period that an initial pause in the received voice energy from an external telephonic unit (20) must exceed to indicate the presence of a live voice in which the pause timer is disabled from timing any pauses until the end of a delay time internal, a second minimum time period which is no longer than the first minimum time period that a pause must exceed after the lapse of the delay time in

Abstract: A call classifier (300, 500) for recognizing cadenced signals (100-103) is based on data tables (110, 111) whose contents define the cadences of the signals that need to be recognized. Consequently, the call classifier may be adapted for recognizing the cadenced signals of various signaling schemes that are used in various countries or telecommunication systems, simply by reprogramming the data contents of the data tables. Each cadenced signal comprises a different pattern of interleaved signal-on (P) intervals and signal-off (S) intervals. A separate cadence timing table-pair (200-204) corresponds to each sequential S/P interval-pair. Each table-pair includes a P table (210) and an S table (211) each having a plurality of entries (220, 221) each corresponding to a different duration of the corresponding P interval and S interval, respectively, and identifying those signals which have the corresponding P interval and S interval duration, respectively, as candidates for a received signal.

Abstract: A telephone answering device (TAD) includes a remote access mode which is operative responsive to dual tone multi-frequency (DTMF) signals. At least three bandpass filters each receive an input signal from a telephone line interface provided in the TAD. A software controlled sampling section receives outputs from all the bandpass filters for sampling outputs from the bandpass filters, the sampling section including a multiplexer which receives the outputs from all of the bandpass filters, and a peak hold circuit coupled to an output of the multiplexer. An analog-to-digital converter receives an output from the peak hold circuit, and a digital controller receives the output of the analog-to-digital converter for controlling operations of the TAD in a remote access mode responsive to the detected DTMF signals. First and second ones of the bandpass filters have respective center frequencies corresponding to frequencies of respective DTMF signals and a third bandpass filter has a different center frequency.

Abstract: An improved dual tone multifrequency (DTMF) or multitone signal detector which more efficiently and reliably detects DTMF signals. The present invention performs twist computations only when the signal has become stable, thus achieving more accuracy and reliability. The DTMF detector receives a plurality of digital samples of a received signal and calculates energy values for each of the plurality of different uncorrelated frequencies. The DSP then determines maximum values of the energy values for each of the two or more frequency groups, referred to as M(1) and M(2), to detect the plurality of tones in the received signal. The DTMF detector then performs improved twist computation and thresholding. The DTMF detector first determines if the M(1) and M(2) values of the respective frame being examined have the same indices.

Abstract: A method of and apparatus for providing compatible universal identification telephone protocols by generating predetermined unique audio sequences recognizable by the telephone user as defining standardized Audio Icon information and distinct from and separated from one another and other telephonically transmitted signals; sending and receiving such generated audio sequences on a public switched telephone network having paths the parameters of which fall within predetermined specified training sets, including modem performance standards; and assuring recognition and correct identification of such audio sequences conveyed along such paths.

Abstract: A method of detecting narrow-band signals in an echo canceller to control the coefficient update process, echo suppression process, and the disablement of the echo canceller is provided. The method includes the steps of searching for the presence of a generic tone, searching for DTMF tones, searching for a 2100 Hz tone and, if a generic tone is found, searching for a dial tone. If a generic tone is detected on the far end signal, a tone flag is set which triggers the disablement of the echo canceller coefficient update process and the enablement of the echo suppressor process. If a 2100 Hz tone is detected, the echo canceller is disabled. If a DTMF signal is detected, DTMF flags are set which are used by the echo suppressor for suppressing the near end echo. Finally, if a dial tone is detected, dial tone flags are set which cause the disablement of the echo suppressor.

Abstract: A tone blocking system and method for use preferably in conferencing systems in order to prevent control tones from being transmitted to other conferees is disclosed. The buffer length used to process the signal and detect tones is varied, being increased when a tone is suspected to allow for sophisticated tone detection algorithms, and being decreased when silence is present by trimming the silence away. The technique minimizes delay, and its degrading effect on echo, but nonetheless provides for a lengthy buffer required to do reliable tone detection. The invention is applicable to any signal other than tone as well.

Abstract: A system and method for recognizing a voice signal on a telecommunications path upon initiation of an outbound telephone call or receipt of an inbound call by an automated calling system. Power magnitudes of a received signal on the telecommunications path are measured over selected increments of time. Calculations are made to measure the variation in power measured with respect to the selected increments of time, and these calculations are then compared to a threshold value for determining whether or not the received signal is a voice signal.

Abstract: A circuit and method for detecting identification signals in a digital input signal (Rx) having signal parameter values which are provided to a signal memory (54). The values provided to the signal memory (54) are updated at a sampling frequency. The circuit includes a set of processing units (50) which are arranged so as to be freely programmable by a user. The signal memory (54) stores values of input signal (Rx) and output signals of the processing units. A programmation memory (56) stores at predetermined locations associated with the inputs of the processing units, the signal memory addresses associated with the signals that the user desires to connect to these inputs. A controller (64) sequentially reads the addresses stored in the programmation memory (56) and provides the values stored in the signal memory (54) corresponding to the read addresses to inputs of respective processing units in an order corresponding to the predetermined locations.

Abstract: Responding by telcommunication terminals to data messages received during the silent intervals of ringing to immediately answer a call, perform monitoring activities, provide selective answering of incoming calls, and perform control functions. For providing selective answering, telephone sets utilizing the invention monitor the incoming data message to determine if an identification code of the telephone set is contained within that message. If the identification code of the telephone set is within the message, the telephone allows ringing at that set. If the identification code of the telephone is not in the data message, the telephone counts the number of ringing cycles, and, once this count becomes greater than a predetermined number, the telephone set allows ringing at the set. For performing monitoring activities, a remote utility meter reader is responsive to it's identification code in a data message to immediately answer the incoming call from a public utility company computer before ringing starts.

Abstract: An improved dual tone multifrequency (DTMF) signal detector which uses the Goertzel DFT algorithm and which utilizes variable or differing frame widths that are frequency dependent for improved detection and reduced error. The DTMF detector includes a codec receiver which receives signals from the transmission media, and a digital signal processor (DSP) coupled to the codec. The DSP receives the digital samples and preferably applies the Goertzel DFT algorithm using differing frame lengths according to the present invention. The DTMF detector utilizes a different frame width for different tones of the possible tone frequencies according to the present invention. Thus the calculation uses a different frame length N for different ones of the uncorrelated frequencies, wherein the different frame lengths comprise at least a subset N of the number of digital samples. The different frame lengths N are designed to optimally align the calculated frequency spectrum at each of the different uncorrelated frequencies.

Abstract: The present invention provides an automatic answering system that, upon being provided with operating power, uses a tone pattern learning operation to identify an applicable busy tone pattern. After the applicable busy tone pattern is identified, when a calling party records a message on a recording medium of the system, the system performs a detection mode subroutine corresponding to the identified busy tone pattern and detects the busy tone in a rapid and accurate manner. As a result, unnecessary use of the recording medium is eliminated.

Abstract: The present invention is related to a telecommunication system and method enabling a user to get access to any of automated call processing systems. The system comprises in combination a telephone line interface means adapted to provide function of a telephone set, a control means connected to the telephone line interface means, and adapted to constantly monitor the telephone line, analyze a call progress and a ring back tone signals and to switch automatically without human intervention from a pulse dialling mode to a DTMF dialling mode upon detection of a ring back signal validated by a central office. This system also includes a handset and keypad means connected to a telephone interface means and the control means. The central office processes calls in a pause dialling mode. The system enables the user to get access to automated call processing systems, the access to which is limited only to callers equipped with a DTMF telephones and central office base DTMF services.

Abstract: Allowing a calling party to enter a message that is transmitted on a destination telephone link during silent intervals of a ringing signal by a switching office. In a first embodiment, the destination telephone link is equipped with the feature of allowing receipt of calling party specified data messages. The switching office automatically accepts information for a data message as dialed digits from the calling party. In a second embodiment, the switching office designates that an originating telephone link can transmit information for a data message. The switching office is responsive to the transmitted information to form a data message and to transmit this data message on a destination telephone link during the silent intervals of the ringing cycles. In a third embodiment, in response to a calling party placing a call to a special telephone number, the switching office requests that the calling party enter a destination telephone number and information for a data message.

Abstract: An emergency locator signal light system, suitable for installation at a residence or business, which in a monitor mode is responsive to the dialing of a predetermined emergency telephone number, such as "911", to enter a command mode. In the command mode, the system is responsive to predetermined tone dialing signal sequences, which are herein termed "Star Codes", to activate an included signal light device. Exemplary "Star Codes" are "*1" for a medical emergency, whereupon red and white lights alternately flash; "*2" for a fire emergency, whereupon a white light flashes; and "*3" for a police emergency, whereupon blue and white lights alternately flash. The "Star Codes" can be dialed either locally from any telephone set or other dialing device at the residence or business from which the "911" emergency call is placed, or by an emergency telecommunicator who makes a decision to activate the flashing lamps in view of the nature of a particular emergency following a verbal description by an emergency caller.

Abstract: This tone detector which is suited for dual tone multifrequency (DTMF) digit detection, separates the pairs of tones into a low frequency and high frequency group in which the other frequency group is attenuated by filtering. The amplitude of the low and high frequency groups serve as separate variable threshold reference signals. Individual tones are bandpass filtered with their corresponding outputs converted into an amplitude signal. The amplitude of the individually bandpass filtered tone signals are compared against the corresponding low or high frequency variable threshold signal for a determination of whether a tone is present. Preferably, additional validation steps are applied to the preliminary tone decisions to provide improved digit detection accuracy, especially in the presence of other signals such as speech.

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, the received signal level is compared to the third threshold (-43 dB) and receipt of a voice signal is indicted if the level of the received signal exceeds this threshold.

Abstract: A sign bit integrator and method for generating a signal to correct an offset in a signal processing system that can distort the output from the system. A charge pulse is generated when the sign of a input signal is sampled in order to provide an offset correction signal with a polarity opposite that of offsets in the system. The charge pulse is provided to a pair of transistors whose size ratio sets the magnitude of the charge pulse. The polarity of the charge pulse is set responsive to a sign bit in the input signal. An integrator capacitor provides the offset correction signal to the signal processing system. A third transistor may be switchably substituted for one of the pair of transistors to change the ratio of sizes and thus change the magnitude of the charge pulse to thereby change the speed with which the offset correction is made. The sign bit integrator and method may be used to correct distortion in a voice signal in a telephone system.

Abstract: A quality monitoring system can detect certain system faults and fraud attempts in a distributed voting system. The system uses decoy voters to cast predetermined check ballots. Absent check ballots can indicate system faults. Altered check ballots can indicate attempts at counterfeiting votes. The system can also cast check ballots at predetermined times to provide another check on the distributed voting system.

Abstract: Apparatus powered from a communications line minimizes current drawn from the line by use of a variable power supply having a DC to DC conversion circuit controlled by an oscillator. The output of the DC to DC conversion circuit in a first lower power drawing mode is used to power a tone detection circuit which monitors the line for a wake-up tone. On receipt of an appropriate wake-up tone, the tone detection circuit provides an interrupt signal to a microprocessor which, in response, causes an increase in the oscillator frequency. The increased oscillator frequency then increases power drawn from the line via the DC to DC conversion circuit for operation in a second higher power drawing mode.

Abstract: A system and method for detecting convergence in an echo canceller prevent false convergence from occurring as a result of receiving only tones in an input signal. An adaptive filter is used in an echo canceller to estimate an echo signal produced by an unknown echo channel. The estimated echo signal is subtracted from the return signal to remove the echo produced by the unknown echo channel. To prevent the echo canceller from falsely converging on a signal which contains only tones a system and method are provided for detecting the presence of tones in the absence of other frequencies. Filter taps of the adaptive filter are filtered to produce a filtered signal. The amount of energy in the filtered signal is compared to the amount of energy in the unfiltered filter taps to determine whether only tones have been present. If only tones have been present, the echo canceller is not allowed to reduce the adaptation step size of the adaptive filter.

Abstract: A DTMF signal judging apparatus includes a first power calculator, and second power calculator and a judging apparatus. The first power calculator calculates the overall power of an input signal or the power of the input signal outside the DTMF frequency band. The second power calculator calculates the power in the DTMF frequency band; or more specifically, calculates the power in both the higher and lower frequency band portions of the DTMF frequency band. The judging apparatus then compares the output from the first and second calculators, and determines whether the input signal is a DTMF signal based on the comparison.

Abstract: The present invention is a two line phone adaptor that allows two separate phone lines to be connected to and controlled by a single line DTMF phone. The two line phone adaptor has one ring detector for each line and one hold circuit for each line. The adaptor also has an electronic line selector circuit, a DTMF decoder and an off hook detector. All of the above circuits are connected to a micro controller that contains the software that defines the functions of the adaptor. The adaptor does not have any user accessible control buttons except for an on/off switch. The adaptor will automatically engage the `ringing line` and transfer the ring signal to the attached phone to generate an audible ringing sound. When the phone is taken off the hook, the adaptor will automatically seize a `free line` for use. The adaptor is controlled by the 3.times.4 keyboard of the attached DTMF single line phone and provides the functions such as music on hold, manual line select and three party conferences.

Abstract: A control device may be connected in series or in parallel to a telephone for restricting or routing calls made from the telephone to take advantage of low cost carriers for intra-LATA calls. The serial or parallel connection of the telephone can be detected as well. The device may be programmed for routing depending on the geographical location of the telephone. The central receiving office of the local phone company can be prevented from routing the call by the use of interfering tones.

Abstract: An improved dual tone multifrequency (DTMF) or multitone signal detector which uses both static and dynamic thresholding techniques to provide an increased functional dynamic range, improved speech immunity for improved detection and reduced error, and simplified signal to noise ratio control. The DTMF detector receives signals from the transmission media, calculates energy values for the different frequencies, and then determines maximum values of the energy values for each of the frequency groups, referred to as M(1) and M(2). The DTMF detector then performs both static and dynamic thresholding according to the present invention to ensure valid tone detection. The static thresholding compares each of the M(1) and M(2) values with a static threshold value to ensure that the maximum energy values have a minimum energy to warrant detection.

Abstract: A DTMF signal judging apparatus includes a first power calculator, and second power calculator and a judging apparatus. The first power calculator calculates the overall power of an input signal or the power of the input signal outside the DTMF frequency band. The second power calculator calculates the power in the DTMF frequency band; or more specifically, calculates the power in both the higher and lower frequency band portions of the DTMF frequency band. The judging apparatus then compares the output from the first and second calculators, and determines whether the input signal is a DTMF signal based on the comparison.

Abstract: In methods and apparatus for estimating the frequency response of telecommunications channels, signals carried on the channels are divided into pluralities of signal segments of limited duration, unvoiced signal segments are identified, and spectral components of the unvoiced signal segments are measured. The measured spectral components may be integrated over time to derive time-averaged measurements of the spectral components. The time-averaged measurements may be compared to corresponding components of expected unvoiced signal spectra to improve the accuracy of the frequency response estimates. Filters may be inserted in the channels to adjust the frequency responses, the filters having filter characteristics selected in response to the measured spectral components. The methods and apparatus can be used to compensate for poor bass frequency response in voice channels.

Abstract: Tone detection may be accomplished by receiving an in-phase signal component 203 and a quadrature signal component 204. These components are then sampled to produce a plurality of sampled in-phase signal components 207 and a plurality of sampled quadrature signal components 208. The sampled in-phase signal components 207, or the sampled quadrature signal components 208, are then shifted by a pre-determined phase angle to produce a plurality of shifted components. Having shifted these signals, the shifted signals, or at least a set of them, are compared with the opposite non-shifted sampled signals, or a set thereof. When each of the shifted signal components substantially match the opposite non-shifted signal components, a tone signal is being received.

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: Methods and apparatus for use in connection with a telecommunication between a local telephone and a remote telephone, which are capable of detecting whether one of the parties to the communication has attempted to initiate a three-way, i.e., conference, call by using a hook-flash signal. The apparatus includes a low pass filter for passing energy having frequencies below about 500 Hz, and an energy detector for detecting a specific electrical energy pulse characteristic of the hook-flash having passed through the low pass filter. The existence of the hook-flash is confirmed by digital signal processing equipment which identifies a rapid drop-off in energy also characteristic of the hook-flash signal. Optionally, the hook-flash may be further confirmed by including software for cooperating with the energy detector to ascertain whether sound has occurred in the telecommunication during a predetermined period following the first hook-flash signal.

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: By testing a received signal for power, frequency content, and stability, one can measurably improve DTMF signal detection and identification performance in voice store and forward systems. The algorithms described here have been found to be especially useful in minimizing talk-off. Further, the approach improves the performance with acoustic-type generators and minimizes transhybrid loss.

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 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 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: Apparatus for detecting single and/or multiple cadenced tone progress status of a telephone call in any one of a plurality of telephone networks is disclosed. A set of parameters for each of a multiplicity of predetermined single and/or cadenced tones in which some call progress status having multiple different sets of parameters for the same call progress status are stored in memory. Parameters of the cadence (s) of a valid tone present on the telephone line are measured and compared with the multiplicity of sets of parameters stored in the memory to establish the presence of the call progress status represented by the corresponding cadenced valid tone. For tones having multiple cadences, the measured parameters of each cadence is compared with a corresponding set of cadence parameters of the memory to establish the presence of the call progress status represented by the multiple cadenced tone.

Abstract: An automatic telephone answering system employs a switch activated by any of several techniques to select a language for communication with a caller. A single matrix determines the content of a message to be generated in response to input from the caller. A single matrix can be used because it is arranged in accordance with the content of the various messages and not on the specific language of the messages. All of the messages for each respective language are stored in a separate directory such that a given identifier obtained from the matrix will recall that message in the language determined by identification of the particular directory. A telecommunications device for the deaf (TDD) is treated in the same manner as a language and selection of messages employs the same matrix used for traditional languages. Received TDD signals are converted to ASCII for storage, and messages to be identified by the matrix are stored in ASCII and converted to TDD before transmission.

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: Method and apparatus for detecting a far-end disconnect signal for use by telephony applications such as voice messaging systems. In a preferred embodiment of the present invention, signal power of a telephone signal in particular frequency ranges is compared with the signal power in these frequency ranges for characteristic far-end disconnect signals used by telephone systems worldwide. Further, the cadence of the signal power of the telephone signal is examined to determine whether the cadence of the telephone signal is characteristic of far-end disconnect signals, including "busy signals" and "dial tones.

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: 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: Apparatus for detecting whether a telephone call has been disconnected, which apparatus includes: (a) a click detector for detecting a click and for generating a "click indication"; (b) a telephone handset impact detector for detecting a telephone handset impact and for generating a "handset impact indication"; (c) a silence detector for detecting silence and for storing a "silent indication"; (d) a timer for determining a predetermined time interval and for transmitting a signal to a controller whenever the time period expires; wherein, in response to the signal, the controller analyzes the "click indication", the handset impact indication", and the "silent indication" to determine whether a predetermined sequence of handset impact, clicks, and silence was detected and, if so, for generating a signal indicating that the telephone call has been disconnected.

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 technique for software ring tone detection is disclosed utilizing, in the preferred embodiment, a recursive algorithm. The technique provides flexibility in that a digital signal processor may be reprogrammed to detect ring tone frequencies and amplitudes present in numerous different countries.

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.