Method and apparatus for suppressing background noise in a digit

Details Method and apparatus for suppressing background noise in a digit Method and apparatus for suppressing background noise in a digit

1974-03-21

1976-11-30

Griffin, Robert L.

Modulators

Amplitude modulator

Nonlinear device controlled by modulating signal

332 11D, 179 1HF, H03K 1322

Patent

active

039952177

ABSTRACT:
An apparatus for suppressing background noise in a companded delta modulated telephone system. The apparatus includes a comparator for comparing a signal related to the analogue input signal to an encoder of the system with a reference signal. The comparator provides an output to reduce the rate of occurrence of a succession of bits which cause companding within the encoder when the reference signal exceeds the other signal to the comparator. This is achieved by altering the step size of a feedback signal within the encoder or modifying the output from the encoder by removing or inverting one of the compand bits. The reference signal is higher than a signal generated by background noise and consequently for signals below the reference signal the decoder reconstructs an analogue signal which is lower in level than the input signal. A method for achieving the result is also claimed.

REFERENCES:
patent: 3500441 (1970-03-01), Brolin
patent: 3582784 (1971-06-01), Gaunt, Jr.
patent: 3609551 (1971-09-01), Brown
patent: 3699566 (1972-10-01), Schindler
patent: 3729678 (1973-04-01), Glasbergen et al.
patent: 3746990 (1973-07-01), Le Diberder et al.
IBM Technical Disclosure Bulletin, "Digital Companding Device for Delta Modulators" by Choquet et al., vol. 15, No. 7, Dec. 1972.

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