We have developed a new method for analyzing and displaying electroglottographic (EGG) signals (and their first derivative, DEGG): the electroglottographic wavegram. The wavegram provides an intuitive means for quickly assessing vocal fold contact phenomena and their variation over time. Vocal fold closing and opening appears here as a sequence of events rather than single incidents, taking place over a certain period of time, and changing with pitch, loudness and register. Multiple DEGG peaks which can occur during both the concacting and de-contacting phase of vocal fold vibration, are revealed in wavegrams to behave systematically, indicating subtle changes of vocal fold oscillatory regime. As such, EGG wavegrams promise to reveal more physiological information on vocal fold closure and opening events than previous methods.
To construct a wavegram, the time-varying fundamental frequency is calculated and consecutive individual glottal cycles are identified. Each cycle is locally normalized in duration and amplitude, the signal values are encoded by color intensity and the cycles are concatenated to display the entire phonation in a single image, similar as done in sound spectrography.
Project team: Christian Herbst, Tecumseh Fitch
Collaborator: Dr. Jan Švec (University Olomouc, Czech Republic)