Fundamental frequency (F0 or "pitch") is the physical variable that reflects what we perceive as intonation or tone of voice.  It corresponds to the frequencies of the large, regular oscillations perceived in the voiced elements of speech. These oscillations originate in the vibrations of the larynx.  Intonation can distinguish a question from a response, express exclamation, or emphasize certain words in a sentence.  Intonation is used differently from one language or dialect to another. Certain languages such as Chinese or Vietnamese use tone to distinguish one word from another.  The voice's fundamental frequency is not the only physical variable associated with intonation.  In English, syllables that seem to be "high" are also characterized by greater amplitudes and are longer than those perceived as being low.

In sum, the analysis of temporal structure attempts to identify the major highs and lows, visible in voiced segments of the speech signal.  The correct identification of the temporal distance between two peaks or two valleys permits us to calculate the fundamental frequency, in other words, how many such peaks or valleys are produced per second.  (Taken from an explanation by E. Keller in the Signalyze˘ Users Manual, 1992.)