thumb|Approximating a [[Square wave (waveform)|square wave by <math>\sin(t) + \sin(3t)/3 + \sin(5t)/5</math>]]
A harmonic spectrum is a spectrum containing only frequency components whose frequencies are whole number multiples of the fundamental frequency; such frequencies are known as harmonics. "The individual partials are not heard separately but are blended together by the ear into a single tone."
In other words, if <math>\omega</math> is the fundamental frequency, then a harmonic spectrum has the form
:<math>\{\dots, -2\omega, -\omega, 0, \omega, 2\omega, \dots\}.</math>
A standard result of Fourier analysis is that a function has a harmonic spectrum if and only if it is periodic.
See also
- Fourier series
- Harmonic series (music)
- Periodic function
- Scale of harmonics
- Undertone series