Variable bit rate speech codec with backward-type prediction and

Details Variable bit rate speech codec with backward-type prediction and Variable bit rate speech codec with backward-type prediction and

1985-01-31

1988-06-14

Kemeny, Emanuel S.

Electrical audio signal processing systems and devices

One-way audio signal program distribution

Public address system

375 27, 375 34, G10L 500

Patent

active

047517360

ABSTRACT:
In an adaptive differential PCM (ADPCM) system transmitter, three quantizers provide, respectively, 3, 4, and 5-bit quantization at the signal sampling rate. Each quantizer produces, in response to an input signal sample, a coded signal I(n) in the form of a bit sequence the number of bits in the coded signal from each quantizer being different. The number of bits comprising the coded signal is proportional to the bit rate. The bit rate can thus be altered by switching the codec output to selected ones of the adaptive quantizers. To eliminate quantizing distortion during bit rate transitions, one adaptive quantizer is caused to operate in the dominant mode, to receive the input signal sample and produce the coded signal I(n). At the same time, the other adaptive quantizers operate in a secondary mode to update their step-size .DELTA.(n) on the basis of the quantized signal produced by the dominant mode quantizer. When a secondary mode quantizer is switched to the dominant mode, minimal time is required for tracking the input signal thereby reducing the quantization distortion during bit rate transitions.

REFERENCES:
patent: 4518950 (1985-05-01), Petr
patent: 4571737 (1986-02-01), Nishitani et al.
patent: 4589130 (1986-05-01), Galand

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