Differences in Shimmer Across Formant Regions

Objectives Objective acoustic measures used to analyze phonatory dysfunction include shimmer and jitter. These measures are limited in that they do not take into account auditory processing. However, previous studies have indicated that shimmer may be processed differently along the tonotopic axis of the ear and, in particular, may be perceptually and physiologically significant around the third and fourth formants. Methods This study investigated the relationship between shimmer around the first four formants (F1–F4) and in the broadband unfiltered speech waveform for 18 normal speakers from the voice disorders database of KayPENTAX. The voice samples were filtered around each formant with a bandwidth of 400آ Hz and then shimmer was assessed using five built-in different measures from Praat software. Results Comparisons of means tests revealed that shimmer increases significantly with formant frequency from F1 to F4, for all shimmer measures. Furthermore, for all shimmer measures, shimmer in the unfiltered speech was significantly and more strongly correlated with shimmer around F1 (rآ =آ 0.45–0.61) and F2 (rآ =آ 0.69–0.74), significantly but more weakly correlated with F4 (rآ =آ 0.42–0.47), and not significantly correlated with F3. Conclusions The findings indicate that there are differences in the shimmer found around the different formants and that shimmer information around F3 and F4 is not well captured in standard shimmer measurements based on the broadband unfiltered waveform.