### ASA 127th Meeting M.I.T. 1994 June 6-10

## 1pSP17. A modulation model for the vowel sound /i/ in human speech.

**Tadd B. Hughes
****
**
*Dept. of Elec. Eng., Univ. of Vermont, 101 Hill St., Apt. 11, Stoneham, MA
02180
*

*
*
**Richard G. Absher
**

**
**
*Univ. of Vermont, Burlington, VT 05405
*

*
*
An approach has been developed that models a nonstationary speech signal
with very low error on a pitch period by pitch period basis using an AM--FM
model. The speech signal is first separated into two independent signals, a
low-frequency signal and a high-frequency signal. AM and FM signals are
extracted from the high-frequency signal through the use of two nonlinear
operators, the integral operator and the overmodulation detection algorithm.
Model parameters are determined by a combination of direct Fourier series
computation and parameter optimization using the correlation error measure and
the Marquardt--Levenberg algorithm. This technique was applied to speech
produced in various gas concentrations of air and helium in order to determine
whether model parameters are directly related to the velocity of sound ratio.
It was found that the amplitudes of the harmonics of the low-frequency signal
were emphasized with the increase of the velocity of sound ratio. The standard
deviation of the carrier frequency of the FM signal tended to increase with the
velocity of sound ratio. The amplitudes of the AM signal had a modal structure,
and the modes were independent of velocity of sound ratio.