Several types of sound sources are activated during speech production: voicing, aspiration, frication, and nasalization. The relative output levels of these sounds, in dB, are determined by the Gain of voicing source (gv) option, the Gain of aspiration source (gh) option, the Gain of frication source (gf) option, and the Gain of nasalization (gn) option, respectively. The default settings for these options are factory preset to maximize the intelligibility of each voice. However, changing the settings can be useful in debugging the system or in demonstrating aspects of the acoustic theory of speech production. You can change the level of one sound source globally. For example, turn off frication to hear just the output of the larynx. You might need to reduce these options to overcome certain kinds of overloads, but try the procedure described in the next section first.