Abstract: A pager system connectable to the existing telephone wiring for activation through the normal residential DTMF telephone instruments, the system including a plurality of pager devices, each connected to the phone line between the tip and ring wires, and each pager including an identification circuit to allow it be individually addressed by a person using the phone, whether or not connection has been made through the central office. For use of the system, the keypad of the telephone instrument is used to enter a sequence of characters (e.g., symbols as well as numbers), which comprise an activation sequence. The DTMF activation sequence includes three parts: a header, a pager address (pager identification PID) and a signal identification (SID). The header portion is a sequence which is not used by the central office as part of its available services. The header portion is a system enabling signal that distinguishes the pager system from central office sequences.

Abstract: To determine whether a received signal represents a dual tone multi frequency (DTMF) code, a characteristic of the received signal is repeatedly measured over a period of time, thereby obtaining a plurality of parameter measurements. This may include separating the received signal into low band and high band signals and for each of the low band and high band signals, determining a plurality of squared magnitude measurements over the period of time. A deviation value is then determined for each of the plurality of parameter measurements, and an average deviation value is determined from the plurality of deviation values. The average deviation value is compared to a threshold value, thereby obtaining a comparison result. The received signal as alternatively designated as representing or not representing a DTMF code on the basis of the comparison result.

Abstract: A multiple tone detector includes n tone detectors, each detecting one of n distinct tones, where n.gtoreq.2, and a background detector which generates a measure of accumulative background energy E.sub.avg in a frequency band or bands which do not include at least a subset of the n tones. The output of the background detector is applied to a smoothing filter, which generates the accumulative background energy measure E.sub.avg for a current frame as a weighted sum of the background detector output for the current frame and the background energy measure E.sub.avg from a previous frame. A parameter controlling response time of the smoothing filter is varied depending upon whether or not speech is determined to be present in the background portion of the input signal. A processor uses the energy measures from the n tone detectors and the background detector to compute n ratios, where a given ratio is the ratio of the energy measure of the ith tone to the accumulative background energy measure E.sub.avg.

Abstract: A method and system for distinguishing valid DTMF signals from spurious DTMF noise includes detecting signals having a first signal component indicative of DTMF signals and having a second signal component having frequencies unrelated to DTMF frequencies. The second component is utilized in isolation from the DTMF frequencies of the first signal component. The analysis includes determining a signal level representative of the second signal component. If the signal level exceeds a predetermined threshold level, the first signal component is determined to be spurious noise. On the other hand, if the signal level is below the threshold level, the first signal component is passed to a DTMF-responsive system, such as a voicemail system or a voice response unit. Optionally, the operation includes requesting confirmation of the signal of interest, if the signal level of the second signal component falls within a range which includes the threshold level as its upper limit.

Abstract: The ADSI system 100 has a file stored in RAM 202 or ROM 204. The file plays a CAS tone. The CAS tone is disguised by playing one or more introductory tones as frequencies lower than the CAS tone. The user is conditioned to receive a CAS tone by ramping the CAS tone amplitude or increasing the amplitude in discrete steps.

Abstract: An echo cancellation scheme for DMT MDSL digital subscriber loop telecommunications data transfer is disclosed. The echoed data stream frame is aligned with the incoming data stream frame. The time domain equalizer trims the lengths of both the DSL channel and echo channel within the length of the cyclic prefix, so that the time domain convolution for synthesizing the echo is accomplished within the FFT process, enabling the echo to be subtracted in the frequency domain.

Abstract: An arrangement relating to telecommunication access and control. An arrangement is provided at least for providing access information for protected subscriptions to at least one telecommunications system which requires the giving of access code information. The arrangement comprises a portable telecommunications unit which includes processing devices, storing devices and loudspeaker devices. The existing processing devices, storing and loudspeaker devices of the portable telecommunications unit are used for transmitting at least DTMF-coded access code information to a communications arrangement to provide access to a number of telecommunications systems.

Abstract: Service node for use in a communications network for providing access to services available to callers using the network. The service node includes a plurality of peripheral devices, a switch for connecting the peripheral devices to external communication links of the communications network for receiving calls made by callers to access a service provided by the service node; a control processor operable to generate a scan pattern representative of a plurality of individual patterns of characters corresponding to respective service commands relating to service options available to a caller, wherein the caller may originate any of the service commands during a call, and a distributed processing system.

Abstract: A method for providing access to services during communication between subscribers over a communication path on a switched communication network is provided. In a first step, the injection of a DTMF service request signal by a first subscriber is detected. In a second step, a service is provided to a subscriber that corresponds to the DTMF service request signal from a set of services. The set of services includes a service that terminates the communication path to a second subscriber.

Abstract: A tone detector for detecting a multi-tone input signal in the presence of speech and noise, comprising first signal processors that generate output signals indicating the energy level of the input signal with the frequency of one of the component tones being amplified and the frequencies of all other of the component tones being attenuated, a last signal processor that generates an output signal indicating the energy level multiplied by negative one of the input signal with the frequencies of all component tones being attenuated, summing junctions that generate output signals indicating the energy levels of the sum of one of the first signal processor output signals and the last signal processor output signal, and tone validation logic receiving the summing junction output signals that generates a tone detect signal when the summing junction output signals indicate that the component tones satisfy a signaling standard.

Abstract: A user-authentication system includes an authorized user device (AUD) for transmission of dtmf tones to a user-verification system (UVS) over a telephone network, where user-verification is performed and authorized users are granted access to a desired service. In a memory module of the AUD, a plurality of passphrases and identifying data are stored for subsequent transmission to the UVS. The compensating system comprises a pair of tone devices that generate low frequency tones and high frequency tones, respective that are amplified to different amplification levels. The amplification levels compensate for the low and high frequency tone transmission characteristics associated with different microphones in use in a public telephone system. The systems further performs channel normalization with the user-activated AUD and the UVS. Tone signals representative of the access telephone number transmitted by the AUD to reach the UVS, have a reference amplitude of zero.

Abstract: A call defeat device to prevent calling unauthorized numbers, such as long distance, 1-900 etc., which is adapted to prevent a caller from successfully dialing one or more predetermined digit strings on a touch tone telephone connected to a given telephone line by apparatus including a touch tone decoder coupled to the telephone line and a microprocessor/memory for storing and issuing predetermined unauthorized digit strings, if dialed on the telephone, designates that the call is to be defeated. A comparator compares each digit string dialed on the telephone to the predetermined digit strings, and, if a match is sensed, a dialer sends onto the telephone line at least one DTMF digit, such as a "#", which will defeat the call in progress.

Abstract: To detect a dual tone pair signal in a telephone communication system, the signal is sampled at the Nyquist frequency. The sampled signal is filtered to determine the top three tone frequency power results. The input signal is then resampled at one-half of the Nyquist frequency. The resampled signal is filtered to determine signal power in the row and column frequency bands. The top three power results from tone filtering and aliasing row and column band pass filter power results are checked for lack of excess power to reject false digits.

Abstract: In a transmission system a pair of signalling tone signals is transmitted by a transmitter (2) to a receiver (6) via a transmission channel (4). In the terminal (6) a tone detector is used to detect the presence of the pair of signalling tone signals. In order to improve the reliability of the tone detector in the case of differing strength of both tone signals, the decision on the presence of the pair of signalling tone signals is based on a combined strength measure which is determined by an adder (23). The combined strength measure is compared with a reference level TH.sub.2. In a further embodiment, also a check on the level of the individual tone signals is done with comparators (11) and (9), in order to specify the maximum strength difference tolerated.

Abstract: Apparatus, and an associated method, for converting an inband signal, such as a DTMF signal, into a form to permit transmission thereof to a receive station. An inband signal, such as a DTMF signal generated by a wireline device is applied to a digital transmitter, such as a fixed cellular terminal having a digital transceiver. The inband signal is detected and encoded. The inband signal is encoded in a manner to permit its transmission according to an appropriate air interface standard.

Abstract: A user-authentication system includes an authorized user device (AUD) for transmission of DTMF tones to a user-verification system (UVS) over a telephone network, where user-verification is performed and authorized users are granted access to a desired service. In a memory module of the AUD, a plurality of passphrases and identifying data are stored for subsequent transmission to the UVS. The UVS includes a memory module for receiving and storing the passphrases and identifying data, and a processor for determining whether user-stated passphrases correspond to the stored passphrases, and for prompting the user with knowledge-based questions and determining whether the identifying data corresponds to answers given by a user in response to the knowledge-based questions.

Abstract: A dual tone multi-frequency detector includes a pulse code modulation expanding unit for converting pulse code modulation data into linear data. A correlating unit constructed from a plurality of correlators correlates the linear data with a plurality of predetermined reference signals to generate a plurality of power values of a frequency band corresponding to dual tone multi-frequency signals. A total power detecting unit detects a total power value of the linear data. A low frequency maximum power detecting unit detects a maximum low frequency power value from the power values of a low frequency band generated by the correlating unit. A high frequency maximum power detecting unit detects a maximum high frequency power value from the power values of a high frequency band generated by the correlating unit.

Abstract: A communication system, and related method, for reliably transmitting DTMF code signals through a low-bit rate channel employing a VSELP speech compression algorithm. The system adds relatively low-level noise to the analog DTMF signals before encoding by the compression algorithm. By adding the low-level noise to the DTMF signals, the tones associated with the DTMF signals can be reliably detected on the receiving end.

Abstract: A user-authentication system includes an authorized user device (AUD) for transmission of dtmf tones to a user-verification system (UVS) over a telephone network, where user-verification is performed and authorized users are granted access to a desired service. In a memory module of the AUD, a plurality of passphrases and identifying data are stored for subsequent transmission to the UVS. The UVS includes a memory module for receiving and storing the passphrases and identifying data, and a processor for determining whether user-stated passphrases correspond to the stored passphrases, and for prompting the user with knowledge-based questions and determining whether the identifying data corresponds to answers given by a user in response to the knowledge-based questions.

Abstract: An input digital sample containing voice and DTMF signal is used as an input to an adaptive filter. The output signal of the adaptive filter is used to generate a residue from the difference between the input sample and the output signal. The residue signal is used to update the coefficients of the adaptive filter. Upon the convergence of the adaptive filter, the residue signal comprises voice reduced DTMF signal while the adaptive filter's output signal contains the detected DTMF signal.

Abstract: A method and device for detecting a customer premises equipment alerting signal (CAS) tone in a telephone system which has both caller identification and call waiting. The present invention distinguishes between valid CAS tones transmitted by the telephone company central office and invalid CAS tones which are caused by music or a human voice. The present invention samples detected tone during a plurality of sample periods. The change of frequency, as well as the direction of frequency change, between successive sample periods is calculated. The number of transitions in the direction of frequency change are counted and used to determine whether the detected tone corresponds to a valid CAS tone or an invalid CAS tone.

Abstract: A signal detection circuit includes band pass filters for detecting frequency components of a Call Alert signal (CAS) signal, a tone detection circuit for detecting whether or not a signal component is present in the output signals of the band pass filters, and two types of guard time setting circuits that have different guard times. When the CAS signal component is present, a transmitting speech signal is muted. Thereafter, with the guard time setting circuit having the normal guard time, it is determined whether or not the signal component lasts for a predetermined time period. Since the CAS signal is detected with two types of guard times, even if the transmitting speech signal contains a frequency component of the CAS signal, the transmitting speech signal is not mis-detected as the CAS signal.

Abstract: The total energy of a signal that has entered from a telephone line is detected before the signal is applied to an AGC circuit. After the signal is applied to the AGC circuit, the energy of a DTMF signal, which comprises one frequency from four high group frequencies and one frequency from four low group frequencies, is detected through a band-elimination filter having a short energy-propagation delay time with respect to pass-band frequencies. By detecting the DTMF signal based upon the detected energies, detection of the DTMF signal can be performed in a short period of time and erroneous detection can be suppressed.

Abstract: An improved dual tone multifrequency (DTMF) or multitone signal detector which more efficiently detects DTMF signals. For each received frame, the present invention initially performs only a portion of the Goertzel DFT algorithm for each of the possible tone frequencies and then analyzes the interim accumulated energies. The DTMF detector then selects one or more frequencies from each of the tone groups which have the largest energy values, and the detector only completes calculation of the Goertzel DFT algorithm on those selected one or more frequencies. In other words, the DTMF detector discontinues calculation of the Goertzel DFT algorithm on one or more frequencies which have low accumulated interim energies. This reduces the computational requirements and provides improved performance.

Abstract: An information signal detection device and an information signal detection method are disclosed with which it is possible to transmit information by means of a DTMF signal using a channel that is prone to distortion, such as a high-efficiency channel. The information signal detection device comprises a filter bank component and a logic component. The filter bank component receives via a channel an information signal in which are superposed sine waves of two different frequencies selected from a specific number of frequencies sent by the sender, and generates binary information patterns showing in binary information whether the signal components of the various frequencies of this information signal are present. The logic component recognizes the end of the signal region when the binary information pattern generated in the binary information pattern generation step is containing no binary information showing that a signal component is present continuously for a specific period of time.

Abstract: A service node provides a shared added value service within a telephony network, such as a public switch telephone network. Peripheral devices, such as speech applications platforms shared announcement platforms and message recording platforms, are connected to a switch which operates under the control of a central control computer. The switch includes distributed processors responsive to externally originating signals, such as DTMF signals, generated while calls are being processed. The distributed processing devices supply information derived form said signals to the central control computer. Thus, it is no longer necessary for a central control computer to examine ongoing calls in order to detect the presence of DTMF signalling. Detection of DTMF signalling is performed locally and information is returned back to the control computer only when relevant information has been detected.

Abstract: With a personal call manager, when a caller calls a primary telephone number for the owner of the personal call manager, the personal call manager selectively routes the incoming call to any combination of local extensions on the owner's premises, and to remote extensions such as a telephone instrument on another premises, a pager, a cellular telephone, a central office voice mail box, and a cellular telephone voice mail box. The personal call manager retains control over an incoming call throughout the duration of the call. Consequently, the owner can route the incoming call to multiple locations, or transfer the call to a telephone answering service at any time after taking the incoming call. Moreover, a call can be handled based on the type of call, e.g., voice, fax, or modem. The personal call manager also permits a user to monitor, either locally or remotely, a message being left with a telephone answering service, e.g.

Abstract: A digital telecommunication network (10) provides an audio processor (56) for each call in each external node (14). The audio processor (56) includes a vocoder and additional functions. At a source external node (14), the audio processor (56) detects DTMF events and encodes the events in a call-related signalling packet (26) which conveys a history of all DTMF activity at the source node over the past several seconds. In addition, the source node detects silence and configures a call-related signalling packet (26) to instruct a destination node (14) how to synthesize comfort noise. Speech is encoded as vocoded voice packets rather than call-related signalling packets. At a destination external node, the node's audio processor (56) distinguishes call-related signalling from vocoded voice. The audio processor (56) synthesizes voice, comfort noise, DTMF signals, and other signals in response to the call-related signalling packets and vocoded voice packets.

Abstract: A system for detecting the presence, in an audio channel which may contain voice signals, of a tone at a frequency selectable from among a plurality of selectable frequencies. A bandpass filter receives the audio input; its center frequency is selectable in response to a control signal. A first detector circuit provides from the output of the bandpass filter an output signal when a tone containing substantial energy at about said center frequency is input to the filter. A band-stop filter having the same center frequency as the bandpass filter also receives the input audio; a second detector circuit demodulates and thresholds the band-stop filter output.

Abstract: A method of dialing digits using dual tone multifrequency (DTMF) signals comprised of generating a digit from a DTMF generator comprised of a first pair of signals forming a DTMF signal, one signal of the first pair of signals being in a low frequency band and one signal of the first pair of signals being in a high frequency band, and applying the DTMF signal to a telephone line connected to a central office, detecting the first pair of signals in an auxiliary circuit and immediately applying a third signal in either of the low or high bands to the telephone line at the same time as the first pair of signals, and detecting the presence of the pair of signals and the third signal at the central office and preventing processing of the DTMF signal at the central office as a result thereof.

Abstract: A technique is provided for enabling remote testing of a telecommunications service provided by an international gateway switch (12). To accomplish such testing, a test facility (10) associated with the switch includes a DTMF interface (16) for automatically answering an inbound call and for verifying if the caller may access the service for testing purposes. The test facility also includes a signal converter (38) for translating DTMF signals entered during the inbound call to yield an activation sequence of signals for input to the international gateway switch to activate the service offered by the switch for testing purposes.

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 for controlling long distance calling in an analog key telephone system having a multi-frequency receiver includes the steps of: connecting the multi-frequency receiver to a telephone connected within the system; determining whether numerical digit inputs corresponding to a complete telephone number are provided from the telephone; determining whether the telephone is provided with a class of service that restricts long distance calling, when numerical digit inputs corresponding to a complete telephone number are provided; determining whether the complete telephone number represents a long distance telephone number, when the telephone is provided with the class of service that restricts long distance calling; releasing a call initiated from the telephone, when the complete telephone number represents a long distance telephone number; connecting the call initiated from the telephone, when the telephone is not provided with the class of service that restricts long distance calling, or when the complete

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 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: A method and apparatus for detecting and recovering from call waiting interference to data communications is disclosed. In a system wherein a first party communicates with a second party via a telecommunications link, the telecommunications link may be disrupted by a third party's attempt to call the first or second party. The present invention detects such a disturbance on the telecommunications line and allows the first or second party to answer the call from the third party. The invention re-establishes communications after the call with the third party is completed.

Abstract: In a voice processing system, a voice detection algorithm is disclosed wherein the sensitivity is adjusted based upon whether or not tones (e.g.; DTMF) are presently being received. In an additional embodiment, the adjustment is made only when the voice processing system is in a predetermined mode.

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 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: 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: DC level control for an electronic telephone line card which filters the DC component from the input audio signal, determines the gain setting of the transmit path, develops a DC adjust voltage opposite to that of the DC shift component and subtracts the DC adjust voltage to the input voltage to cancel the DC shift component. A quantized, discontinuous feedback path is implemented to respond only to DC shifts so the AC operation remains substantially unaffected. Such discontinuous feedback eliminates stability and impedance matching problems introduced with continuous feedback solutions. A DC control circuit according to the present invention includes a low pass filter for detecting DC shifts, a quantizer for asserting an incremental signal, a threshold detector for activating adjustment functions, and an accumulator for developing the DC adjust voltage by incremental steps.

Abstract: An apparatus adapted to be activated by an input device for accessing a function code in a telephone comprises a first memory for storing a function code, a second memory electrically connected to the first memory for storing a datum corresponding to the function code, and an address decoder electrically connected to the input device and the second memory for decoding a signal generated from the input device and designating thereby an address to access at least one of the function code and the datum, wherein the function code stored in the first memory and the datum stored in the second memory are accessible by same the address. This apparatus effectively reduces the number of the keys required on a keypad of a telephone and is provided for a simplified operation.

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: 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: In a telephone exchange apparatus for performing exchange processing by a memory time switch, first tone signals are generated, and second tone signals are generated by sequentially exchange-controlling the memory time switch in synchronism with the zero-crossing points of the generated first tone signals. Furthermore, when the second tone signals are sent to corresponding output time slots, the switching operation is performed in synchronism with the zero-crossing points of the second tone signals, so that high-quality tones including no harmonic component can be sent to an extension telephone set or to another system through an outside line.

Abstract: A method and apparatus for utilizing DTMF tones and supervisory tones in a call processing system to adjust parameters for future tones and/or speech. The tones initially received are analyzed to determine characteristics such as signal-to-noise ratio, twist, signal level, etc. Processing parameters for future tones and speech are adjusted based upon the characteristics of a first tone.