Synchronized compressor and expander voice processing system for

Details Synchronized compressor and expander voice processing system for Synchronized compressor and expander voice processing system for

1977-01-24

1978-10-31

Griffin, Robert L.

Amplifiers

Signal feedback

Combined with control of bias voltage of signal amplifier

325 65, 179 1SC, 330254, 333 14, H04B 164, H03G 700

Patent

active

041237110

ABSTRACT:
The voice processing system for radio telephone consists of a compressor in the transmitter and an expander in the receiver. The compressor divides the input voice signal into syllabic groups and applies a gain to each syllabic group depending on the peak amplitude of the signal of the respective group, resulting in a reduction or compression of the dynamic range of the voice. The expander on the other hand increases or expands the dynamic range of the signal restoring the voice to its original form. The compressor and expander are synchronized such that the amount of expansion or instantaneous gain in the receiver is exactly the reciprocal of the amount of compression in the transmitter, i.e. when the gain of the compressor is N, the gain of the expander is 1/N. In this way the total system gain is always unity and is therefore transparent to voice and other analog signals passing through it. A porton of the voice frequency band is pre-empted to carry a digital signal to synchronize the compressor to the expander. This band designated as the control channel is located between 2500 to 2700 Hz and is used to carry binary frequency shift keyed (FSK) data stream which defines the instantaneous gain of the expander denoted by N. The band between 300-2500 Hz is used to carry the compressed voice. The effect of noise encountered in the transmission path is reduced because the soft syllables are amplified to the same amplitude as the loud syllables thus achieving an improved signal-to-noise ratio.

REFERENCES:
patent: 2959641 (1960-11-01), Hufnagel
patent: 3193775 (1965-07-01), Herrerd et al.
patent: 3458815 (1969-07-01), Becker
patent: 3681756 (1972-08-01), Burkhard et al.
patent: 3732371 (1973-05-01), Burwen
patent: 3969680 (1976-07-01), Wermuth
patent: 4001505 (1977-01-01), Araseki et al.
A Monolithic Analog Compandor, Craig. Todd., IEEE Journal of Solid-State Ckt., vol. SC-11, No. 6, Dec., 1976.

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