The frequencies of overtones in a normal harmonic series are directly related to integer multiples of the fundamental frequency. In contrast, inharmonicity is the extent to which the frequencies of individual overtones deviate from integer multiples of the fundamental frequency.

In a musical context, percussion instruments such as chimes or cymbals often create strong inharmonic overtones, but the effect is also present in many other instruments, most notably the piano, and is directly responsible for the concept of stretch-tuning.

This term describes a type of oscillating arrangement involving a non-linear relationship between the restorative force and the oscillation amplitude. As a result, the oscillating period is dependent on the amplitude of oscillation. This is not the case in a true harmonic oscillation.

In a musical context, based on an equal temperament scale, the term enharmonic usually refers to equivalent musical notes which have the same pitch (frequency) but are denoted in different ways. For example, F# is enharmonic with Gb. However, while these two musical notes represent the same pitch, the choice of one or the other denotion would depend on the musical key and/or chord progression of the particular musical work. 

An alternative meaning for the term applies where the musical scale is not based on an equal temperament, and thus Ab does not have precisely the same pitch (frequency) as G#. In this case enharmonic refers to notes which are very close in pitch — much closer than a semitone difference — but not absolutely identical.

Seen Sine Wave