Observations on Frequency-Domain Companding for Audio Coding

Frequency-domain companding can be used in conjunction with audio coders that produce white coding noise. In [1-2] it is demonstrated empirically that this technique colors white coding noise so that it is better masked by audio signals, resulting in higher perceived audio quality. This paper offers additional theoretical background and empirical results on this companding technique. A simplifying assumption in [1-2] is analyzed, the effect of the companding exponent a on the spectral flatness measure is investigated, and optimal values of a are identified for PCM and ADPCM speech coding. [1] R. Lefebvre & C. Laflamme, "Spectral amplitude warping (SAW) for noise spectrum shaping in audio coding," Proc. 1997 IEEE ICASSP, Munich, Germany, April 1997, pp. 335-338. [2] R. Lefebvre & C. Laflamme, "Shaping coding noise with frequency-domain companding," Proc. 1997 IEEE Workshop on Speech Coding for Telecommunications, Pocono Manor, PA, Sept. 1997, pp. 61-62 Demonstration files.

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