International Telephone and Telegraph Corporation

James Grant Dunn

Philip Duncan Carmichael

John Richard Cowan

Thomas Chungmin Chen

Anthony Joseph Russo

Anthony Frank Presto

In the transmitter portion a multiplexer multiplexes first digital data and first teletype signals to provide first digital data signals. The first digital data signals are converted into second digital data signals having a different form than the first digital data signals by a Viterbi coder. A PSK modulator responsive to the second digital data signals provides a first PSK signal for transmission. In the receiver portion a PSK demodulator receives a second PSK signal containing third digital data signals having multiplexed second digital data and second teletype signals with the third digital data signals being extracted from the second PSK signal. A Viterbi decoder converts the third digital data signals into fourth digital data signlas having a different digital form than the third digital data signals. A PSK demultiplexer is responsive to the fourth digital data signals to separate the second digital data and the second teletype signals for utilization. The arrangement to extract the third digital data signals from the second PSK signals includes the PSK demodulator and a Costas' type phase locked loop including a number controlled oscillator, a digital phase shifter, an accumulator arrangement including three accumulators accumulating different data and errors, a clock recovery circuit and a loop filter controlling the number controlled oscillator.

Digital PSK modem

This invention relates to a digital vocoder where speech is translated to a digital version thereof. An adaptive filter in the form of an N stage Itakura type cascade derives from the speech a prediction residual and N spectral parameter in the form of weighting coefficients of the filter. The pitch period, derived from the prediction residual, the voiced/unvoiced decision derived from the first of the weighting coefficients and the peak amplitude of a pitch pulse, and a digital signal representing filter gain, derived from the last of the weighting coefficients are multiplexed with each other and the N spectral parameters for transmission to a receiver. The receiver employs an excitation generator responsive to the pitch period, the gain signal and the voiced/unvoiced decision to produce an excitation signal to excite an N/2 cascade connected stage receive filter. Each stage of the receive filter operates on a time shared basis on an adjacent pair of the N spectral parameters. The receive adaptive filter operation is the inverse of the transmit adaptive filter so that after digital to analog conversion the original speech is substantially reproduced.

Digital vocoder

There is disclosed a digital conference bridge for a delta modulated switching system having information transmitted by delta modulation bits in M channels of a time division multiplex frame, where M is an integer greater than three. N conferees, where N is an integer greater than two but less than M, are interconnected by a time switch to enable a conference to take place among the conferees. N three stage shift registers are provided, one for the delta modulation bits of each of the conferees. N sequence detectors are coupled to an associated one of the shift registers to produce a binary 1 output when bits stored in the shift register are all binary 1 or all binary 0. N counters each have their count increased by the binary 1 output of an associated one of the sequence detectors. A count comparator is coupled in common to all the counters and produces a control signal indicating a new speaker for the counter having the largest count. A selection matrix is coupled to each shift register and responds to the control signal to couple the delta modulation data of the new speaker through a one stage memory to the time switch for distribution to all of the conferees.

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Upper Montclair, NJ, United States of America

James Grant Dunn