On the Performance of Speech Waveform Coders with Noise Spectral Shaping

The performance of speech waveform coders that incorporate a noise spectral shaping filter is discussed. The coders studied are adaptive pulse code modulation (APCM), adaptive differential PCM (ADPCM), and adaptive delta modulation (ADM). For APCM and ADPCM, the noise shaping filter is designed to minimize the C-message weighted quantization noise power. As for ADM, the noise shaping filter is used to move some portion of in-band noise outside the signal band. Simulation results show that the performance improvement of these waveform coders with spectral shaping is about 0.5-3 dB over the systems without noise shaping. Although this improvement is relatively small, the waveform coders with noise spectral shaping yield subjectively more pleasing and intelligible sound than those without it.