The Electroglottographic Spectrum as an Indicator of Phonatory Activity
Résumé
Although the electroglottographic (EGG) signal is not acoustic, one might expect that some of the source-induced variation in the spectrum slope of the airborne signal would be present also in the EGG signal. Wideband spectra of EGG signals were evaluated from sustained and intermittent phonation under various conditions, including changes of electrode position, vowel, subglottal pressure and SPL. Recordings were made of subjects producing /pV/ utterances with simultaneous acquisition of EGG and intraoral pressure. The EGG spectrum envelope was found to be quite linear in dB/octave, with the exception of the fundamental partial. The EGG spectrum effects of vowel changes were negligible. EGG spectrum slope change with SPL was large at phonation onset and small in loud phonation. Additionally, recordings from an existing database of 8 trained male singers were analysed for EGG spectrum variation with SPL. The singers performed crescendo tasks on sustained tones, with a typical SPL variation of up to 20 dB from soft to loud. The corresponding EGG spectra had slopes of -14 to ‑9 dB/octave. The variation in EGG spectrum slope was again small, on the order of one quarter of the slope variation in the airborne spectrum. Occasionally, ripple in the EGG spectrum envelope was present, due to double peaks in the time derivative of the closing part of the EGG waveform. We conclude that the EGG spectrum slope appears to offer a convenient contacting criterion, but will be harder to use for judging vocal effort beyond contacting.