A comparison of the performance of four low-bit-rate speech waveform coders

Subjective ratings were obtained for four different speech waveform coders of varying complexity at each of three bit rates (24, 16, and 9.6 kb/s). atc (adaptive transform coding) is rated the highest and adpcm-f (adaptive differential pcm with a fixed predictor) the lowest, regardless of bit rate. Although there is large variability in the ratings due to different talkers and listeners, sbc (sub-band coding) is rated higher than adpcm-f and about equal to adpcm-v (adaptive differential pcm with a variable predictor) for most talkers and listeners. A weighted combination of two objective measures, one accounting for noise and the other for bandwidth effects, appears promising as a predictor of the subjective quality ratings.