Raymond S. Medaugh - Middletown NJ
AT&T Bell Laboratories - Murray Hill NJ
Accumulation of distortion possibly resulting from multiple digital code conversions is prevented by including in an ADPCM-to-PCM decoder (100, FIG. 1 or 600, FIG. 6) an arrangement (119, FIG. 1 or 601, FIG. 6) for making a trial transmission of the resulting PCM sample (. PSI. (k)) to obtain (via 209, FIG. 2) a composite noise value (. alpha. (k)) for the PCM sample (. PSI. (k)). The composite noise value includes noise components resulting from both quantizing the code word and truncating digital signals used in the decoder and subsequent coder. The composite noise value is evaluated (via 211) to determine whether adjustment of the PCM sample value (. PSI. (k)) is necessary.
In one embodiment (FIG. 1, 100), a reconstructed linear version (Y. sub. r (k)) of the PCM sample is adjusted (via 216, 218, 220 or 221) when the composite noise value (. alpha.