Harmonic Distortion - Odd and Even Harmonics

What is harmonic distortion and what are odd and even harmonics. A critical subject that encapsulates all things tube, solid state, amp driven etc.

Dynamic Processors

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I am sure you have heard the term ‘harmonic distortion’ banded around in the industry when the subject of distortion, saturation etc rear their heads, and I am sure it has confused you to some degree. Hell, even us pros get a little confused once in a while. So, it helps to have the subject explained both easily and visually and I have tried to do that here.

What is harmonic distortion

In an analogue 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.

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.

Harmonics are simply multiples of the fundamental frequency of a sound and the addition of harmonics within a sound define 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.

Generating odd and even harmonics

To fully grasp this subject it is probably best to use a harmonic generator plugin on your music and ascertain how the various harmonics affect the sound. There are some free harmonic generators out there and some are very good. Hornet Harmonics is very useful but if you want to use a harmonic generator to learn from then Chris Budde’s Christortion plugin reigns supreme. However, check that it will work on your system as the plugin is quite old.

Christortion allows you to mix and blend various harmonics to the fundamental but it’s real power comes in the form of its GUI. You can see, in real-time, how the harmonics affect the waveform. Additionally, you can invert the harmonics which allows for another level of processing.

BUT, as always, I believe in coupling some theory with a lot of application and to demonstrate it to you visually and with working before and after audio examples.

In the video I explain the subject of harmonic distortion in detail showing you how to generate both odd and even harmonics. I show you how to apply different harmonics on a sound and explain the settings in detail.

Plugins used in this video:

Sound Forge

Budde’s Christortion

Topics covered in this video are:

  • What is it, how does it work, what are odd and even harmonics
  • Fundamental
  • Phase
  • Additional Harmonics
  • Overdriving
  • Amps
  • Generate