消失的基频（missing fundamental）是心理声学（psychoacoustics）领域常被谈论的现象。周期信号的基频即为信号的音高，但基频信号的强度大小却不一定大过泛音强度大小，有时基频信号的强度大小甚至为零，这种情形即为我们所谓的消失的基频。 在日常生活中，一般的乐器的声音均是由基频与倍频（泛音）组合而成，而基频就是影响声音音高的主要因素之一。然而，当我们将基频的强度以人为得方式调整为零时，会发现被调整过后的声音音高仍旧不变。 此一现象虽然让音高在频谱上的判别更加困难，但也被应用于信号处理领域。

A harmonic sound is said to have a missing fundamental, suppressed fundamental, or phantom fundamental when its overtones suggest a fundamental frequency but the sound lacks a component at the fundamental frequency itself. The brain perceives the pitch of a tone not only by its fundamental frequency, but also by the periodicity implied by the relationship between the higher harmonics; we may perceive the same pitch (perhaps with a different timbre) even if the fundamental frequency is missing from a tone.