Perceptual Audio Coding using Adaptive Pre- and Post-Filters and Lossless Compression

This paper proposes a versatile perceptual audio coding method to achieve high compression ratios and with capabilities for low encoding/decoding delay. It accommodates a variety of source signals (including both music and speech) with different sampling rates. It is based on separating irrelevance and redundancy reductions into independent functional units. This contrasts traditional audio coding where both are integrated within the same subband decomposition. The separation allows for the independent optimization of the irrelevance and redundancy reduction units. A psycho-acoustically controlled adaptive linear filter is used for the irrelevance reduction, and the redundancy reduction is carried out by a predictive lossless coding scheme, which is termed weighted cascaded least mean squared (WCLMS) method. Experiments are carried out on a database of moderate size which contains mono-signals of different sampling rates and varying nature (music, speed, or mixed). They show that the proposed lossless coder outperforms other competing lossless coders in terms of compression ratios and delay, as applied to the pre-filtered signal. Moreover, an informal comparison of the combined pre-filter/lossless coder with a state of the art perceptual audio coder (PAC) indicates that the new method achieves a comparable compression ratio and audio quality with a lower delay.