Impact of noise and encoder/decoder mistracking on ADPCM system performance

An analytic expression is derived that characterizes the distortion occurring in an adaptive differential pulse code modulation (ADPCM) system, when the system encoder and decoder mistrack, in the presence of quantization and coded channel noise. These expressions demonstrate that, when such mistracking occurs, the presence of channel and quantization noise is further accentuated by the transfer function of the mistracked coder system. These results are subsequently extended to the case of coarse quantization where it is shown that in addition to the previous disorder a further term is introduced into the coder transfer function that, depending on the coarseness of the encoder quantization process, can derive the compound system unstable even when the decoder is tracking the encoder