EGG (Electroglottograph)

The electroglottograph (EGG) is a small device that lets us follow the vibrations of the vocal folds from outside the body. When paired with VoceVista, it gives a second, physiological signal alongside the audio — one that comes directly from the source of the voice and is unaffected by the vocal tract that shapes everything downstream of the folds.

How the Signal Is Acquired

A small high-frequency current flows between two electrodes held in place on either side of the larynx. The conductance between the electrodes increases slightly when the vocal folds make contact, because the contacting tissue forms a continuous conductive path; it falls again when the folds part. The modulations in conductance, recorded over time, give the EGG signal — a measure of vocal-fold contact over the cycle of vibration.

The procedure is non-invasive: nothing enters the mouth or throat, and the small current is harmless. The signal is acquired through a separate hardware module and arrives at VoceVista as a second channel synchronised with the audio.

What the EGG Reveals

Because the EGG is a near-direct view of the glottal source, it complements what the audio shows in two important ways:

  • It is unaffected by the resonances of the vocal tract. Two singers producing the same vowel may produce very similar audio spectra, but their EGG traces can be quite different — and conversely, the same EGG pattern can underlie very different vowels.

  • It makes voice phenomena that are hard to hear in the audio easy to see. Register transitions, fold approximation, breathiness, pressed phonation, and pathology all leave characteristic signatures in the cycle-by-cycle shape of the EGG.

The most commonly read features of the EGG are the closed quotient (the fraction of each cycle during which the folds are in contact) and the closing and opening events — the moments when contact begins and ends. These events are sharper and more reliable in the derivative of the EGG (often called dEGG), where they appear as positive and negative peaks rather than as transitions in slope.

Applications

The EGG is most widely used by:

  • singers and singing teachers, to study register transitions, onset coordination, and fold approximation in ways the audio alone does not show;

  • speech-language pathologists, to characterise voice disorders and monitor therapy through measurable contact behaviour rather than perceptual judgement alone;

  • voice scientists, who use the EGG as a near-source reference signal in studies of the source–filter division.

In VoceVista

The EGG signal is shown alongside the audio in the EGG (Electroglottograph) view, available in VoceVista Pro. Display options for the EGG, the dEGG, and the Wavegram are configured in EGG Display Settings.