Tutorial for ISIMP-2001 Recent Developments in Advanced Audio Processing

When DVD and home theater systems become more popular these days, high fidelity multichannel (5.1 channel or 10.2 channel) audio systems are well received in the market. Compared with the traditional mono or stereo audio, multichannel audio requires a much more efficient coding scheme for its storage and transmission. This talk will present two new multichannel audio coding techniques: (i) the use of the Karhunen-Loeve Transform (KLT) to decorrelate signals of multiple channels; and (ii) the use of bit-layer coding to achieve an fully embedded bitstream. We exploit the inter-channel redundancy inherent in most multichannel audio sources, and prioritized the transformed channel transmission policy. Experimental results show that, compared with MPEG AAC (Advanced Audio Coding) algorithm, the proposed MAACKL (Modified Advanced Audio Coding with KLT) algorithm not only reconstruct better quality of the multichannel audio material at regular low bit rate of 64 kbits/sec/ch, but also achieves quality scalability in the single multichannel audio bit stream. The embedded multichannel audio coding system inherit the efficient inter-channel de-correlation block in MAACKL algorithm, and add an progressive quantization coding block and a context-based QM noiseless coding block. The final bit stream generated by this embedded multichannel audio coding system has a fully progressive property, which can terminate the encoding or decoding at any arbitrary point. Experimental results show that, compared with MPEG AAC algorithm, the reconstructed multichannel audio using the proposed algorithm achieves better performance not only with objective MNR (Mask-to-Noise Ratio) measurement, but also with subjective listening test at various bit rates.