Abstract: A system of the present invention includes a sound source for providing sound in the oral-nasal cavity, a microphone to receive sound modulated by the user's mouth, tongue, teeth, and lips as he or she speaks or attempts vocalization, and a circuit. The circuit, coupled to the microphone, generates an output simulating a male or female voice that conveys the modulation as intelligible speech. In one embodiment, the sound source provides subaudible sound. In another embodiment, the circuit includes a sampling circuit for digital signal processing. In yet another embodiment, the circuit with a transducer constitute the sound source for providing overtones and diagnostic waveforms in the mouth. According to a method of the present invention, a modulated sound signal with a first period is received from an oral-nasal cavity and used to form a second signal having a longer period for conveying the first signal's modulation at a lower fundamental frequency.