On the use of direct vector quantization in LPC-based analysis-by-synthesis coding systems

It is shown that, within the framework of LPC (linear predictive coding)-based analysis-by-synthesis coding, the codebook search can be implemented without the filtering operation, thus alleviating the complexity problem and allowing the quantizer to be structured for fast-search quantization. In the proposed scheme, the vector quantizer bypasses the filter and direct-vector-quantization (DVQ) is used for quantizing the input vectors. It is demonstrated that this algorithm performs as well as (if not better than) the conventional analysis-by-synthesis system for short-frame (low delay) applications. Although the DVQ may be significantly less complex (depending on the type of fast-search VQ used), its signal-to-noise ratio and perceptual performance are the same as those of the conventional low-delay CELP (codebook-excited linear prediction)