Adaptive Frequency Warping for Improved Spectral Modeling

The compact representation of harmonic amplitudes in the sinusoidal coding of voiced speech is often achieved by the all-pole modeling of a spectral envelope. The perceptual accuracy of the representation may be enhanced by the use of frequency-scale warping prior to LP modeling. The effectiveness of a frequency warping function has been shown in previous work to depend on the underlying signal spectral shape as determined by phoneme quality as well as voice quality. This suggests the possibility of minimizing the perceived degradation due to LP modeling by adapting the warping function to the local signal spectrum. In this paper, an investigation is conducted to determine possible correlations between preferred warping condition and easily computable spectral cues. Experimental results are presented that demonstrate the advantage of adapting the warping function to the signal spectral envelope in the context of a sinusoidal speech coding scheme.