Performance improvements using synchronous code correction in ADPCM/PCM tandem connections

A sufficient condition for the existence of tandem distortion accumulation is described. The distortion for a sample time at which the sufficient condition is satisfied is studied. It is shown that the transcoding distortion is greater than the adaptive differential pulse code modulation (ADPCM) distortion when synchronous code correction is not used and less than the ADPCM distortion when synchronous code correction is used. These results are combined to show that when synchronous code correction is used, the upper bound of the single transcoding distortion is determined by the single transcoding distortion when synchronous code correction is not used. This bound cannot be generalized for multiple tandem cases