Pitch and speech-rate conversion using envelope modulation modeling

This article describes a method of intelligible speech representation that uses narrow-band envelopes and their carriers. This method enables modification of the talker´s voice pitch and speech-rate without sacrificing intelligibility. The carrier, which shows the instantaneous phase, conveys pitch information, while the temporal envelope conveys speech-rate information and preserves speech intelligibility. The carriers, however, can be replaced by sinusoidal signals without severely degrading intelligibility or voice quality. Consequently, we can modify the pitch by shifting each envelope´s carrier-frequency and convert the speech-rate by stretching or shrinking the envelopes. These findings could be useful in frequency scaling of the speech spectrum to assist hearing-impaired listeners or in time scaling of the speech signal for speech signal reproduction.