Abstract: An apparatus for controlling the operational status of echo canceling in an echo canceler is disclosed. A digital signal processor (DSP) module (52) is configured to provide two bandlimited filters (66, 68). A CAT filter (66) detects the exclusive presence of a continuity assurance. Test (CAT) tone, and a disable filter (68) detects the exclusive presence of an echo canceling disable tone. Outputs from the DSP module (52) couple to a controller module (64), and a control output from the controller module (64) couples to an echo canceler module (54). The control output causes the echo canceler module (54) either to provide echo canceling or to bypass echo canceling. Upon detection of the CAT tone (106), the control module (64) enables echo canceling (88). After the CAT tone disappears (90), the control module (64) monitors the disable filter (68) to determine whether the disable tone is being transmitted (94). If the disable tone is detected, the control module (64) disables echo canceling (100).

Abstract: In an adaptive digital filter for use in an echo canceller or a decision feedback equalizer in a digital data transmission system, reduced storage and lower arithmetic processing speed are attained by subsampling, in effect, the later parts of the waveform, i.e. the tail portion which changes relatively slowly. Such an adaptive digital filter comprises a storage device, such as a shift register, for storing a group of bits which represents symbols being transmitted in the digital data signal, a first stage for deriving an estimate for a first group of the stored bits, and at least one second stage for deriving an estimate for a second group of stored bits occurring earlier in time than the first group. The second stage has a summing device for summing the second group of bits to generate a quantity representing the cumulative sum of the symbols represented in the group, and a multiplier for multiplying the quantity by a single coefficient to obtain an echo estimate for the second stage.

Abstract: A voice conference system using echo cancelers. The system consists of at least two microphone to send out voice signals to a remote location, and a loudspeaker which receives in voice signals from the remote location. To prevent the microphone from picking up the loudspeaker sound, each microphone is hooked to the separate terminal of a comparator. Thus the a person's voice in one microphone will pass, but the loudspeaker sound being received equally by both microphones will be cancelled.

Abstract: A Dual-Tone Multi-Frequency (DTMF) Generator produces a row and column tone frequency for application to the input of two source follower buffer stages. The outputs of the buffers stages are combined in summation operational amplifier to generate the DTMF Signal. There is a voltage level shift between the input and output terminal of the source followers which can be compensated with a self-compensated circuit. With a perfect match between the compensated signal and the source follower, the operational range of working voltage can be about 1.8V to 5V, and the generator can tolerate threshold voltage variation of the transistors.

Abstract: A digital echo suppression circuit in a four-wire digital telephony circuit having an echo from a local or remote connection to a two-wire circuit or other echo source. The invention incorporates a simple method of using the sample pairs from the first and second sampling circuit to produce a control signal from a control circuit. If the subscriber signal is "louder" than the network signal, then the subscriber signal is passed through. If the network signal is louder than the subscriber signal, the interrupter is activated and a zero level is substituted for the subscriber signal in transmissions toward the network. The invention uses the scheme of comparing instantaneous signal amplitude and using the larger amplitude to set a threshold value. The signal setting the threshold then remains the "loudest" until such time as the other signal can exceed the threshold.

Abstract: A telephone line loop current regulator combines the functions of current regulation, current detection, loop disconnect signalling and speech switching. It comprises a gyrator circuit formed by resistor (R1), capacitor (C1), transistor (T1) and resistor (R3). Loop current is regulated by transistor (T1) and resistor (R3) while loop current detection is achieved by monitoring the voltage across resistor (R3) by an opto-diode which forms part of an opto-electronic coupler (OP2). Speech switching is performed by transistor (T3) which also monitors the voltage across resistor (R3) so that speech is switched onto the line via transformer (TR1) when d.c. loop current is present. Line seizure and loop disconnect signalling are carried out by switching the opto-coupler (OP1) to turn the transistor (T1) on and off.

Abstract: In a digital switch high data rate data communications system, such as a "Datapath" system following the "T Link" protocol, to intercouple data terminal equipment operating at different data rates, voice messages are concurrently interleaved in transmitted bit streams. The system includes echo suppression modules for voice transmissions, but for data transmissions the echo suppression means is disabled in a channel by digital simulation of a monofrequency tone to open the channel. The preparatory sequence includes predetermined byte sequences which initiate the exchange of version identifier and parameter data prior to selection of a common data rate for intercommunication.

Abstract: A method of reconstructing an analog signal, particularly for digital telephony, comprises a first step of digital-to-analog conversion, wherein a first reconstruction of the analog signal is provided by introducing a distortion component into the frequency spectrum whose amplitude decreases with the signal frequency, and a second step of filtering carried out by means of a reconstruction filter provided with integrators and having a cut-off frequency F.sub.t. That attenuating distortion component is utilized instead of one of the integrators in the reconstruction filter, to afford a reduction of the overall design of the circuit device operating in accordance with this method, and bring about, as a result, decreased occupation of the integrated circuit and power dissipation.

Abstract: An echo canceler is disabled by sending two signals to it or in the alternate, by sending a single signal. The two signals are bit shifted replicas of each other. The nature of the sequence of the bits within the signals assures that one of the two signals or in the alternate case, a single signal will disable the echo canceler. All of these signals are not necessarily comprised solely of tone at a predetermined frequency; rather they may merely have sufficient energy at a disabling frequency and sufficient signal noise ratio to disable the echo cancelers.

Abstract: An improved switched-loss, adaptive speakerphone dynamically adjusts its switching thresholds and other performance parameters based on an analysis of acoustic environment and telephone line conditions. To access these conditions, the speakerphone utilizes a computer with associated firmware. As part of a calibration process, the speakerphone computes its thresholds before each use to compensate for possible variations in hardware circuitry therein. This is achieved by passing a first and then a second level of a test tone signal through the hardware circuitry and measuring the resulting response. The speakerphone also measures the acoustics of the room in which it operates as part of the calibration process. For this measurement, a tone burst signal is generated through a loudspeaker in the speakerphone and measured by a microphone also in the speakerphone. A time-domain acoustic response of the room is obtained which provides to the computer the amplitude of the return signal and the duration of its echo.

Abstract: An echo cancellation modem for full-duplex communication over a channel with a remote device in accordance with one of several possible modulation schemes suitable for different channel qualities, respectively. The modem includes an echo canceller for reducing echo components appearing in the channel signal while leaving a residual echo component in the echo reduced channel signal, a monitor for determining the quality of the channel based on an analysis of the residual echo component, and a controller for selecting an acceptable modulation scheme, based on the analysis of the monitor. The modem selects the acceptable modulation scheme prior to data communication and it also requests changes to the appropriate level of modulation during data communication when the monitor indicates that the channel quality has changed significantly. The modem requests the remote device to operate at the selected rate and begins operating at the selected rate only if the remove device concurs.

Abstract: A line powered telephone interface circuit answers an incoming call and, responsive to a command tone, routes the call to a selected terminal. If no command tone is received within a predetermined time period, low voltage audio signalling devices located near the conventional telephone sets are activated to alert the subscriber of an incoming call. The interface need not be connected to a separated supply source. The device is connected to a telephone line and to at least one plug connectable with a telephone set jack, the device being connected to various terminals. A detector detects the ring signal and a relay establishes connection with a telephone line as soon as the ring signal has been detected for a determined time duration. A combination timer/switcher circuit inhibits the ringing of the corresponding telephone set, and is associated with a sound transducer connected operable by a low voltage signal.

Abstract: A telephone on-hold device (10) for use with a telephone handset having a handpiece (18) with a mouthpiece (22) and an earpiece (16), the telephone on-hold device (10) comprising a switch (24) located in a housing (12), the housing (12) being dimensioned to receive at least the mouthpiece (22) of the handpiece (18) to actuate the switch (24), and an audio generation device (26) having an audio transducer (39) located in the housing (12) and arranged to be adjacent the mouthpiece (22), the switch (24) having a first switch component (24a) connected to actuate the audio generation device (26).

Abstract: A dial signal generator supplied with dial data corresponding to a dial number, includes a dial data register for storing the dial data, a decoder for decoding the dial data supplied from the dial data register to thereby generate corresponding row and column numbers based on a dual tone multi-frequency (DTMF) system, a DTMF generator for generating a DTMF signal from the row and column numbers generated by the decoder, and a dial pulse generator for generating a dial pulse signal from the dial data supplied from the dial data register.

Abstract: An echo canceller is described comprising an adaptive filter (15). The adaptation rate of the adaptive filter (15) is controlled by means of a control unit (29) determining the appropriate control signal in response to its input signals (x(k), u(f), e(k)). If the described echo canceller is inserted, for example, in the subscriber set of a telephone network, the adaptation process is to be effected only when the far-end subscriber is talking and the near-end subscriber is silent. If such a decision is automatically made with the associated signals (x(k), u(k)), an erroneous decision may at least temporarily considerably degrade the quality of the telephone communication. For this reason, the adaptation rate of the adaptive filter (15) is provided to be controlled in a gradual manner by means of the control unit (29) in response to suitably chosen mean values of its three input signals (x(k), u(k), e(k)), when the far-end subscriber is talking.

Abstract: A receiver for a digital data transmission system comprises a sampling device for sampling digital data signals received from a subscriber loop. A precursor equalizer connected to the output of the sampling device equalizes, in effect filters, the sampled digital data signal. A timing recovery circuit connected to the output of the precursor equalizer controls the sampling device in dependence upon the filtered digital data signal. The precursor equalizer has a difference equation such that the equalized digital data signal has at least one zero-crossing occurring substantially one baud before the main cursor of each pulse. For twisted wire pair subscriber loops, the precursor equalizer may have a different equation: ##EQU1## which produces a single precursor zero-crossing. Alternatively, the precursor equalizer may have a difference equation: ##EQU2## which produces two precursor zero crossings, y(n) being the input to the filter, w(n) its output, h.sub.0 the main cursor height before equalization and h.sub.

Abstract: An echo reduction circuit that may be used to reduce the returned echo in communication links with signficant delay. By making effective use of the echo-masking effect of near-simultaneous desired speech energy and the redundancy present in normal speech, the circuit makes possible wide bandwidth, non-choppy, perceived distortion-free, and perceived echo-free teleconferencing. The circuit performs a rapid time constant, semi-waveform-following partial attenuation of a preemphasized version of the returning transmit signal proportional to a calculation of the likely strength of the returned echo in relation to the strength of the local speech.

Abstract: The present invention provides a control circuit for controlling the path of voice and data signals in a communication system which comprises at least a speaker phone, a cellular transmit/receive unit (TRU), a cellular (CU) handset and a computer having at least a communications software program, a keyboard and an I/O port for communications. The control circuit receives voice and data signals from a plurality of different input sources and routes or switches the received voice and data signals to different selectable destinations. The control circuit comprises analog switching circuitry, a CPU, a modem, landline interface circuitry, TRU interface circuitry and cellular handset interface circuitry which are operatively connected together.

Abstract: A process and apparatus for a voice controlled attenuation adjustment in telephone transmission circuits is disclosed. Signals in the sending and receiving directions are decomposed into sub-band signals in a set of frequency sub-bands. Each frequency sub-band is associated with an attenuation device for each direction of transmission. Depending on the level of activity in each direction in a particular sub-band, the attenuation values of the attenuation devices of that particular sub-band are adjusted. The sub-band signals are then recombined.

Abstract: A memory dial telephone finder includes a casing integrally made on the mainframe of a microprocessor controlled telephone system, which casing is having two guide posts set at both lateral sides for positioning therebetween of a plurality of telephone number index cards, which index cards are having cuttings for quick finding. A plurality of memory keys are mounted on the mainframe in front of the casing to respectively control the mainframe memory which is having the data of the telephone numbers stored therein. A cover which is pivoted to the casing and controlled by an expansion spring to be in a normal open position is having a raid made at the front inner side for sliding therealong of a snapper, and a plurality of locating holes for alternatively positioning of the snapper. A stop plate is pivoted to the casing at the inner front position and pressed by a torsional spring to be in a position constantly retained with the cover.