Improved Noise Weighting in CELP Coding of Speech - Applying the Vorbis Psychoacoustic Model To Speex
This work addresses speech coding quality for audio codec users, but it is incremental as it enhances an existing method without changing the bit-stream.
The paper tackled improving noise shaping in CELP speech coding by applying the Vorbis psychoacoustic model to the Speex codec, resulting in a significant quality increase equivalent to a 20% bit-rate reduction at high bit-rates.
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.