At&t Bell Laboratories

American Telephone & Telegraph Co., At&t Bell Laboratories

Guido Bertocci

Stephen M Walters

Nevio Benvenuto

In an ADPCM coder and decoder including a so-called locking-unlocking adaptation speed control, the adaptation speed is locked to a very slow, almost constant, speed of adaptation for voiceband data and partial band energy signals, i.e., tones and tone like signals, and is unlocked to achieve a fast speed of adaptation for speech. When a so-called partial band energy signal is being inputted, the adaptation speed is biased toward the unlocked state and when a transition occurs from a partial band energy signal to another such signal, the adaptation speed is set to the totally unlocked state and coefficients of an adaptive predictor are set to prescribed values. This is done in both the coder and decoder to minimize generation of impulse noise in the decoder output.

ADPCM coder-decoder including partial band energy transition detection

A bit compression multiplexer (FIG. 2) for a pair of time division multiplexed digital bit streams each one of which includes a plurality of PCM encoded signals deposited in separate and distinct channels of a repetitive frame and signaling bits multiplexed therewith. The PCM encoded signals of successive frames are normally bit compressed (23) into n-bit signals, but periodically the encoded signals of a frame are bit compressed into n-1 bit signals. The bit compressed signals of the pair of bit streams are time division multiplexed (24) with each other, with the multiplexed compressed signals occupying separate and distinct channels of a repetitive frame. The signaling bits are extracted (21) from the pair of digital bit streams and are inserted (24) into predetermined n-1 bit channels of the last-recited repetitive frame. The signaling bits that are placed in a given channel are related to the encoded message signal of that channel.

Growing community of inventors

Neptune, NJ, United States of America

Guido Bertocci