An exploration of skin acceleration level as a measure of phonatory function in singing.
Two kinds of fluctuations are observed in recording phonetograms of singing. Sound pressure level (SPL) can vary due to vibrato and also due to the effect of open and closed vowels. Since these vowel variations are mostly consequences of vocal tract modification and are not directly related to phonatory function, it could be helpful to suppress them when phonation is the focus of study. Skin acceleration level (SAL), measured at the jugular notch and on the sternum, might be less influenced by effects of the vocal tract, and is therefore explored in this study as an alternative measure to SPL. Five classically trained female singers sang five vowels on selected pitches and in different tasks. Recorded data was used to investigate two null hypotheses: 1)Vowel changes generate an equal amount of variation in both SAL and SPL and 2) SAL and SPL are equally correlated to subglottal pressure (Ps).
Somewhat unexpectedly, there was a very small vowel variation effect for both SPL and SAL. In comparison to previous speech studies, these results point to a difference between speech and singing voice which would affect analysis methodology. Furthermore SAL, when compared to SPL, did not correlate more to Ps. Nonetheless, interesting outcomes were found for SAL in relation to phonetogram use. SAL exhibited practically no dependence on fundamental frequency, rather, its major determinant was the musical dynamic. This results in a non-sloping, square-like phonetogram contour which could be easier to interpret than is the conventional SPL phonetogram.