Measuring the effect of fundamental frequency raising as a strategy for increasing vocal intensity in soft, normal and loud phonation

A method is presented to estimate the effect of intentional raising of fundamental frequency (170) on vocal intensity. The method, energy of the synthesised period (ESP), is based on computation of the energy of a hypothetical speech sound synthesised using a single period of the glottal volume velocity waveform and a digital filter that models the vocal tract. If the intensity of speech is regulated by modifying either the characteristics of glottal flow or the vocal tract, the change in the ESP-value should correspond to an equal change in the value of the sound pressure level (SPL). However, F0 can only change the value of SPL, but has no effect on ESP. Hence, by comparing the behaviours of SPL and ESP, it is possible to measure the way in which speakers use F0 raising as a strategy to increase vocal intensity. The results show that, in producing loud voice, speakers use F0 to increase the number of glottal closures per time unit, which increases rapid fluctuations in the speech pressure waveform, which, in turn, raises vocal intensity. The average increase of SPL due to this active use of F0 was approximately 4 dB in loud speech produced by both female and male speakers. (C) 2002 Elsevier Science B.V. All rights reserved.