Analysis of digital and analog formant synthesizers

A digital formant is a resonant network based on the dynamics of a second-order linear difference equation. A serial chain of digital formants can approximate the vocal tract during vowel production. In this paper, the digital formant is defined and its properties discussed, using z-transform notation. The results of detailed frequency response computations of both digital and conventional analog formant synthesizers are then presented. These results indicate that the digital system without higher pole correction is a closer approximation than the analog system with higher pole correction. Finally, a set of measurements on the signal and noise properties of the digital system is described. Synthetic vowels generated for different signal-to-noise ratios help specify the required register lengths for the digital realization. A comparison between theory and experiment is presented.