Intelligibility of speech with filtered time trajectories of spectral envelopes

The effect of filtering the time trajectories of spectral envelopes on speech intelligibility was investigated. Since the LPC cepstrum forms the basis of many automatic speech recognition systems, the authors filtered time trajectories of the LPC cepstrum of speech sounds, and the modified speech was reconstructed after the filtering. For processing, they applied low-pass, high-pass and band-pass filters. The accuracy results from the perceptual experiments for Japanese syllables show that speech intelligibility is not severely impaired as long as the filtered spectral components have 1) a rate of change faster than 1 Hz when high-pass filtered, 2) a rate of change slower than 24 Hz when low-pass filtered, and 3) a rate of change between 1 and 16 Hz when band-pass filtered.