The synthesizer allows K.I.T.T. and K.A.R.R. as well as other similar vehichles logic modules to speak and communicate. Other sounds, such as a police raid to fool criminals or a wild animal's growl, could also be simulated. The Voice Synthesizer "speaks" through the Voice Modulator in the interior of the vehicle.
K.I.T.T.'s primary spoken language was English, however by accessing his language module, he could speak fluently in Spanish and French. The module could also be adjusted to give K.I.T.T. different accents; for example, in Episode 413: Out of the Woods, KITT uses a "New York City" accent and calls Michael, "Micky".