INTERACTIVE EFFECTS OF LOCAL SMOOTHING WINDOW SIZE AND FUNDAMENTAL-FREQUENCY ON SHIMMER CALCULATION

Slow amplitude modulation of human voice was approximated by a sinusoi dal wave. The theoretical effects of smoothing window size, F0, and mo dulation frequency on window amplitude average as well as calculated s himmer were mathematically derived. Subsequently, the theoretical pred ictions were tested using idealized.and real voice, signals from norma l speakers. The theoretical and experimental results suggest that shim mer (when calculated using a smoothing window) is a function of window duration and modulation frequency. Window duration when defined as a constant number of pitch periods varies from speaker to speaker depend ing on their F0. It may not be desirable to use local smoothing window s with a constant number of cycles for shimmer computation, especially if voices with known low-frequency amplitude modulations but notably different fundamental frequencies are compared.