The electroglottograph sends a minute high-frequency electric current between the two electrodes. The variations in resistance as the glottis opens and closes (resistance is less when there is no gap between the vocal folds) are the basis for the EGG signal, from which the program determines the closed quotient.
There is considerable variation among subjects with respect to the strength and quality of EGG signals. Correct placement of the electrodes and good contact between their surface and the neck is essential for the best signals. The photo in Getting Started shows the proper position of the electrodes on opposite sides of the larynx, for one subject. It is suggested that the user experiment by trying various positions while phonating and observing the signals in the monitor. Note that the distance between the electrodes is adjustable by moving their position on the Velcro backing.
The elastic ribbon is supplied to hold the electrodes in place and free the hands. It may give a slight “tight collar” effect at first, but usually one becomes accustomed to it in time. Some users may prefer to keep the electrodes in place manually. This can also improve the contact.
Care should be taken that the contact between the electrodes and the skin be optimal. Signals generally improve in time as the skin warms up and perspires a bit. Moistening the electrodes with saliva can help, as can a special electrode gel (see www.parkerlabs.com/spectra360.html).
If the EGG signal should overbalance the Audio signal in a given subject, it may be necessary to increase the distance between the electrodes in order to attenuate the EGG signal.
- Position the electrodes onto the Velcro-tape of the elastic ribbon to maximize signal output.
- In some cases, you may see an improvement in electrode performance by adjusting the distance between them on the Velcro-tape that holds them in place. Remove the electrodes from the Velcro-tape of the ribbon by placing a fingernail between the Velcro of the elastic ribbon and Velcro on the rear side of the electrodes. This is to prevent the Velcro on the rear of the electrodes from becoming detached (the Velcro tape is fastened to the paint rather than directly to the plastic surface).
- If the Velcro-tape becomes detached from the electrodes together with the paint, the bare plastic housing is exposed to provide a better surface on which to stick the spare Velcro squares that are supplied in the small plastic bag.