A good singing voice has a wide dynamic and tonal range, controlled pitch and the ability to produce various timbres. Voice timbre can be influenced via adjustments of the vocal tract or directly at the sound source in the larynx. This chapter concerns changes at the sound source and how they influence the oscillations of laryngeal tissue, which create a train of airflow pulses. The wave shape of these pulses plays a central role in the voice timbre. The shape of the flow pulses is mainly influenced by (1) adjustments of the vocal tract; (2) cartilaginous adduction (controlled through the degree of breathiness); and (3) membranous medialization (controlled via the choice of chest vs. falsetto register in singing). This chapter proposes a pedagogical model that incorporates the latter two parameters.