International Business Machines Corporation

Other

Stanley M Head

Constantine Michael Melas

Emil Hopner

John W Fennel, Jr

Robert J Hallett

A user-orientated telephone instrument including high-fidelity speech encoding, encryption capability and many function presently provided by centralized call processing is described. Utilizing an ADPCM encoding process including forward error correction, a high quality relatively noise immune signal is provided. To the user, the instrument appears as a unique electronic telephone which offers many special services to facilitate communications with other people and with computers. Advanced features such as optional hands-off voice on/off-hook control, personal identification by voice print and remote chart presentation are provided.

High fidelity speech encoding for telecommunications systems

In reconstructing the analog waveform from a syllabically companded delta modulated digital signal transmitted over a TDMA communication channel operating at near its maximum channel capacity, the noise created in a mid-talkspurt freeze-out is greatly reduced by interpolating the amplitude of the waveform during the freeze-out at the receiver as that of the waveform in the previous period. This makes the quality of voice transmissions in the face of freeze-outs substantially better than prior art techniques which induce background noise during freeze-outs, without the necessity of transmitting a voice activity compression (VAC) mask to control the operation of the interpolation apparatus in the receiver. The interpolation occurs for the first 15 msec sampling period following either a freeze-out or a true VAC operation. The interpolation operation is supplied only once so that if two or more consecutive sampling periods occur at the receiver where no channels are received for a particular voice port, the background noise is injected into the voice port. This prevents the uncontrolled repetition of the interpolation at the end of a talkspurt.

Apparatus to reduce the effect of a mid-talkspurt freeze-out

For a delta modulated signal wave comprising a digital carrier wave modulated by an analog wave and represented accordingly as a bivalued digital data bit stream, a correlation function factor is generated by delaying the bit stream in time by an integral multiple of bits and accumulating the successive individual products over a predetermined number of bits of successive individual bits delayed in time and the corresponding currently appearing bits. The circuitry is extremely simple; readily procurable components only are required. A dual input exclusive OR (XOR) gating circuit is connected to the source of delta modulated signal bit stream and to an N-bit digital binary shift register also connected to the source. A stream of successive bivalued products of the current bits and the time delayed bits over a period of N-bits is obtained from the XOR gating circuit and applied to a bidirectional digital counting circuit from which an autocorrelation function factor is delivered.

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Los Gatos, CA, United States of America

Stanley M Head