Optimum bit allocation and decomposition for high quality audio coding

Current audio compression schemes are capable of reducing the per channel bit rate of high quality audio signals from 16 bits per sample to around 2-4 bits per sample. In these schemes, knowledge of psychoacoustics is utilised and a uniform or nonuniform frequency decomposition method is used. In this paper we derive the optimum bit allocation to achieve the highest perceptual quality under a fixed bit rate, for an arbitrarily decomposed, critically sampled, filter bank. The resultant optimum bit allocation gives rise to a shaped reconstruction noise floor approximately parallel to the masking threshold level. Perceptual coding gain is defined and should be maximized for an optimum decomposition performed by the filter bank. Optimum band splitting is discussed and it is pointed out that decomposition in the manner of critical band splitting does not lead to optimal performance.