Signal-to-noise and idle channel performance of differential pulse code modulation systems – particular applications to voice signals

Analysis leading to a figure of merit for differential pulse code modulation (DPCM) systems with linear feedback networks is presented. It is shown that the figure of merit can be optimized. Simple DPCM has a 6-dB advantage in signal/quantizing noise ratio over pulse code modulation (PCM) for speech. Optimization yields at most 4 dB more. Computer simulation of the system using actual speech samples leads to data supporting the figure of merit as a useful measure of performance for DPCM systems with four digits or more. The simulation also provides data on the error spectrum as a function of quantizer loading and on the probability density of the quantizer input as a function of loading. Performance of the optimum system as a function of increasing feedback network complexity is also shown. Idle channel performance of a particular system is analyzed, indicating the presence of inband oscillations in many cases. The best quantizer bias from the point of view of idle channel performance is found. The level of idle channel noise in DPCM is shown to be approximately equivalent to that in PCM.