Harmonic Distortion screen shows an image of scattered waveforms

When we talk about distortion the image, invariably, conjured up is that of a guitarist thrashing his guitar with acres of overdrive. However, I am more interested in covering harmonic and non-harmonic distortion in subtle ways using non-linear systems rather than using a specific overdriven effect like guitar distortion or a fuzz box etc.

In an analog system overdriving is achieved by adding a lot of gain to a part of the circuit path. This form of distortion is more commonly related to overdriving a non-linear device. But it doesn’t end there as any form of alteration made to audio being fed into a non-linear device is regarded as distortion even though the term is quite a loose one and not too helpful. The idea is to create harmonic distortion and this is the area I want to explore in this chapter.

Harmonic distortion means that additional harmonics are added to the original harmonics of the audio being fed. As all sound carries harmonic content, and this is what defines its timbre, then it makes sense that any additional harmonics will alter the sound quite dramatically. Harmonic distortion is musically related to the original signal being treated and the sum of the added and original harmonics make up the resultant harmonics. The level and relative amounts of the added harmonics give the sound its character and for this we need to look at the two main types of harmonic distortion: odd and even order harmonics. The exception to this is digital distortion which sounds unpleasant and the reason for this is that the digital distortion is not harmonically related to the original signal.

Harmonics are simply multiples of the fundamental frequency of a sound and the addition of harmonics within a sound defines the sound’ timbre and character. Even order harmonics are even multiples of the source frequency (2, 4, 6, 8 etc) and odd-order harmonics (3, 5, 7, 9 etc) are multiples of the source frequency (fundamental).
Even order harmonics (2, 4, 6 etc) tend to sound more musical and therefore more natural and pleasing to the ear and higher levels of this can be used as the ear still recognises the ‘musical’ content. Odd order harmonics tend to sound a little grittier, deeper and richer and higher levels of this cannot be used as abundantly as even-order harmonics as the ear recognises the non-harmonic content and it results in an unpleasant effect. But there are uses for both and depending on how the harmonics are treated some wonderful results can be achieved.

Extract taken from the Creative Effects eBook

If you prefer the visual approach then try this video tutorial:

Harmonic Distortion – Odd and Even Harmonics