Missing fundamental

The missing fundamental phenomenon is the perceptual phenomenon of hearing a pitch corresponding to the lowest (fundamental) harmonic when presented with sound made of a set of frequency multiples (overtones), even when it is actually absent. This can be used to simulate lower frequency sounds with speakers that cannot actually play those frequencies, by playing the overtones that are within its range.

It is established in psychoacoustics that the auditory system, with its natural tendency to distinguish a tone from another, will persistently assign a pitch to a complex tone given that a sufficient set of harmonics are present in the spectrum.

For example, when a note (that is not a pure tone) has a pitch of 100 Hz, it will consist of frequency components that are integer multiples of that value (e.g. 100, 200, 300, 400, 500.... Hz). However, smaller loudspeakers may not produce low frequencies, so in our example, the 100 Hz component may be missing. Nevertheless, a pitch corresponding to the fundamental may still be heard.