ADPCM Encoder/decoder with zero code suppression
AssigneeNorthern Telecom Limited
InventorAndreas H. Weirich
Life of this patent
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Abstract
An ADPCM encoding/decoding arrangement produces n-bit ADPCM codes which have 2.sup.n -1 possible codes, excluding the all-zeroes code. A range of error signals about zero is quantized by the encoder as a non-zero ADPCM code. In order to avoid such non-zero codes resulting in undesired changes of predictor coefficients of an adaptive predictor of the arrangement, updating of the predictor coefficients in dependence upon a reconstructed error signal derived from the ADPCM signal is inhibited when each such non-zero code occurs.
Claims12
An ADPCM decoder, for decoding an ADPCM signal produced by quantizing an error signal zero magnitudes of which are quantized as a predetermined non-zero ADPCM code, comprising:
- an inverse quantizer for producing a reconstructed error signal from the ADPCM signal;
- means for producing a reconstructed signal from the reconstructed error signal and a predicted signal;
- an adaptive predictor for producing the predicted signal from the reconstructed signal and the reconstructed error signal in dependence upon predictor coefficients, the adaptive predictor including means for adapting the predictor coefficients in dependence upon a leakage function and in dependence upon the reconstructed signal and the reconstructed error signal;
- and
- means for inhibiting adaptation of the predictor coefficients in dependence upon the reconstructed signal and the reconstructed error signal when the ADPCM signal has the predetermined non-zero ADPCM code.
A method of decoding an ADPCM signal produced by quantizing an error signal, zero magnitudes of the error signal being quantized as a predetermined non-zero ADPCM code, comprising the steps of:
- producing a reconstructed error signal from the ADPCM signal;
- producing a reconstructed signal from the reconstructed error signal and a predicted signal;
- producing the predicted signal by adaptive prediction from the reconstructed signal and the reconstructed error signal in dependence upon predictor coefficients which are adapted in dependence upon a leakage function and in dependence upon the reconstructed signal and the reconstructed error signal;
- and
- inhibiting the adaptation of the predictor coefficients in dependence upon the reconstructed signal and the reconstructed error signal when the ADPCM signal has the predetermined non-zero ADPCM code.
Dependencies are inferred from the claim text.