f0

F0, or the fundamental frequency, is the lowest frequency of a periodic waveform and corresponds to the rate at which a sound source vibrates. In voiced speech, F0 equals the vibration frequency of the vocal folds and largely determines the perceived pitch. In musical contexts, F0 refers to the pitch of a musical tone, the basic frequency from which overtones are derived. The concept is central to voice and audio processing, where F0 tracking supports tasks such as speech recognition, speaker identification, vocal-tract analysis, and singing voice synthesis.

F0 is typically measured in hertz (cycles per second) and is estimated with algorithms such as autocorrelation, cepstrum-based methods, and the YIN algorithm. F0 is defined only for voiced segments of speech or sound; unvoiced sounds (like many fricatives) do not have a periodic vocal source and thus do not have a well-defined F0.

Typical F0 ranges vary by speaker. Adult males commonly have F0 roughly between 85 and 180 Hz, adult females between about 165 and 255 Hz, and children at even higher values. F0 can vary with age, gender, speaking style, health, and emotional state, and it changes over time as part of natural intonation and prosody. In singing, F0 aligns with musical pitch and is influenced by musical temperament and performance practices. In linguistics, F0 contours encode intonation and, in tone languages, contrastive meaning through pitch variations.

Challenges in F0 estimation include noisy environments, rapid pitch changes, vibrato, and multi-speaker or polyphonic signals, which can complicate reliable pitch tracking.