Improved Noise Weighting in CELP Coding of Speech - Applying the Vorbis Psychoacoustic Model To Speex

TL;DR

This paper enhances CELP speech coding by integrating the Vorbis psychoacoustic model into Speex, significantly improving quality at high bit-rates without altering the bit-stream, and demonstrating broad applicability to other codecs.

Contribution

It introduces a novel noise weighting approach for CELP codecs using the Vorbis psychoacoustic model, leading to quality improvements without changing the existing bit-stream.

Findings

Significant quality increase at high bit-rates

Equivalent to 20% bit-rate reduction

Technique applicable to other CELP codecs

Abstract

One key aspect of the CELP algorithm is that it shapes the coding noise using a simple, yet effective, weighting filter. In this paper, we improve the noise shaping of CELP using a more modern psychoacoustic model. This has the significant advantage of improving the quality of an existing codec without the need to change the bit-stream. More specifically, we improve the Speex CELP codec by using the psychoacoustic model used in the Vorbis audio codec. The results show a significant increase in quality, especially at high bit-rates, where the improvement is equivalent to a 20% reduction in bit-rate. The technique itself is not specific to Speex and could be applied to other CELP codecs.