On the linearity of the relationship between the sound pressure level and the negative peak amplitude of the differentiated glottal flow in vowel production

The negative peak amplitude of the differentiated glottal flow (d(peak)) is known to correlate strongly with the sound pressure level (SPL) of speech. Therefore, the function between d(peak) and SPL has been conventionally modeled as a single line. In this survey, the linearity of the function between d(peak) and SPL is revisited by analyzing glottal flows that were inverse filtered from speech sounds of largely different intensities. It is shown that SPL-d(peak)-graphs can be modeled more accurately by using two linear functions, the first of which models soft phonation, and the second of which models normal and loud speech sounds. For all of the analyzed SPL-d(peak)-graphs, the slope of the modeling line matching soft phonation was larger than the slope of the line for normal and loud speech. This result suggests that vocal intensity is affected not only by the single amplitude domain value of the voice source, d(peak), hut also by the shape of the differentiated glottal flow near the instant of the negative peak. (C) 1999 Elsevier Science B.V. All rights reserved.