Voiced and unvoiced speech differ in whether source is glottal oscillation or frication noise

Evidence

In Figure 5.11, speech production is finally reduced into a signal model, the so-called source–filter model. In voiced signals (in phonation), the source is the glottal oscillation and in unvoiced sounds the source is frication noise created in a constriction or a transient sound generated by rapid release of pressure when a vocal tract closure is opened. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 600

Categorization

• DEFINE: The source-filter model: the core distinction governing all of speech synthesis and coding.