BIT RATES IN AUDIO SOURCE-CODING

Waveform coding of audio signals at low bit rates generally results in coding errors. In high-quality applications these must remain inaudible. The bit rate required to code audio signals without audible errors depends on both the signal's power spectral density function and masking properties of the human ear. It is shown how rate distortion theory and psychoacoustic models of hearing can be used to compute lower bounds to the bit rate of audio signals with inaudible distortion. Subband coding applications to magnetic recording and transmission are discussed in some detail. Performance bounds for this type of subband coding systems are derived.