Variability of phonetograms.

Various sources of phonetogram variation were investigated, i.e. graphs showing voice sound pressure level (SPL) for a speaker's loudest and softest phonation at different fundamental frequencies. The short-term SPL variation within a vocalization was analyzed for 10 female and 10 male normal speakers and for 10 female patients with nonorganic dysphonia, i.e. patients with insufficient voices and no indication of pathology according to microlaryngostroboscopy. This variability was about 5 dB in soft phonation and less in loud phonation. The agreement between 2 investigators independently determining SPL for identical vocalizations by means of a sound-level meter was also studied and found to be quite good. The long-term variation was analyzed in 1 male and 1 female normal subject in 15 phonetogram recordings made on different days; the standard deviation averaged across fundamental frequency and subjects was found to be approximately 3 dB. The implications of these findings for a clinical use of phonetograms are discussed.