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Abstract

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.

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First Claim