Reduced rate ultra low delay audio coder using multistage vector quantization

Communication applications are usually delay restricted, especially for the instance of musicians playing over the internet. This requires a one-way delay of maximum 25 msec and also a high audio quality is desired at feasible bit rates. The Ultra Low Delay (ULD) audio coding structure is well suited to this application and we investigate further the application of multi-stage vector quantization (MSVQ) to reach a bit rate range below 64 Kb/s, in a scalable manner. Results at 32 Kb/s and 64 Kb/s show that the trained codebook MSVQ performs best, better than KLT normalization followed by a simulated Gaussian MSVQ or simulated Gaussian MSVQ alone. The results also show that there is only a weak dependence on the training data, and that we indeed converge to the perceptual quality of our previous ULD coder at 64 Kb/s.