Fine-granular scalable and error resilient audio coding by tree-structured quantization
This paper presents a scheme for scalable, error resilient coding of audio signals. The scheme is implemented here as part of a subband-based audio codec and involves the union of two interconnected ideas: tree-structured vector quantization (TSVQ) and reallocation of bits (RoB). The former ensures that the encoding procedure results in fixed-length codes while the latter is a low-complexity scaling algorithm that computes optimal bitrates for each subband when the bitstream needs to be downscaled to a lower bitrate. The functionality enabled by these two systems assumes great importance when the encoded material is to be delivered over channels and networks that have a time-varying bitrate, such as IP-based wireless networks. Such channels are often error-prone and the potentially debilitating effects of introduced errors are mitigated by the inherent fixed-length property of all codewords. We present results that highlight the performance of this system under noisy conditions and show that the degradation in quality is graceful.