Relationships between intra-speaker variation in aerodynamic measures of voice production and variation in SPL across repeated recordings.

Intra-speaker variation in aerodynamic and acoustic measures of voice production across repeated recordings was studied in relation to cross-recording variation in SPL for three normal female and three normal male speakers. Group data for 15 females and 15 males served as the statistical reference. The speech material consisted of syllable strings in soft, normal, and loud voice. Measures were made of (a) parameters characterizing the inverse filtered oral airflow waveform, (b) the inferred average transglottal air pressure and glottal airflow, and (c) SPL. The results showed that intra-speaker parameter variation across recordings was generally less than 2 standard deviations relative to group mean values. In terms of relation to variation in SPL, the measures could be divided into two main groups: (a) For air pressure, AC flow, and maximum flow declination rate, both intra-speaker variation across recordings and inter-speaker (group) variation was related systematically to variation of SPL. For these measures, it is suggested that variation across recordings was due in part to SPL differences, which can be adjusted for statistically, thus facilitating comparisons between absolute values. (b) For other measures, neither intra-speaker variation across recordings nor inter-speaker group variation was systematically related to SPL. However, some of these latter measures changed with SPL in an orderly fashion across soft, normal, and loud voice for individual speakers. The results are discussed in terms of the clinical use of these measures in studies of voice disorders.