Distortion is one of the fundamental signal processing tools we have at our disposal. Mix expert Bruce Aisher explains how we can use distortion effects in musically creative ways.
In its broader signal processing sense, ‘distortion’ is the generic term for virtually anything which changes the shape of a signal, usually in an undesirable way. However, in audio terms – and especially in production terms – it generally refers to the deliberate introduction of an effect or process which shapes the wave and makes the sound somehow ‘dirtier’.
Any audio system (whether analogue or digital) has a limit to the signal levels it can comfortably handle. Attempting to push a signal beyond that limit will usually result in distortion. In some cases – such as most valve-based circuits and many solid-state analogue circuits – the resulting distortion is generally perceived as quite a pleasant sound. At very low levels, that could be something like tape saturation or a warm ‘overdrive’ effect created by gently pushing an analogue circuit. At more extreme levels, think fuzz effects and guitar amp distortion.
Digital distortion tends to be harsher, rougher and less pleasing to the ear (but that doesn’t necessarily mean it can’t be useful in music production).
Sine Of The Times
The easiest way to demonstrate what happens when a signal distorts is to begin with a sine wave (click the images to enlarge).
The sine wave sounds clear and pure, with no harmonics other than the fundamental frequency:
By applying a distortion plugin, its easy to see (and hear) the effect of adding distortion. If we increase the ‘gain’ setting on the plugin, we replicate the effect of overdriving a circuit by increasing the level of the signal being fed through it.
We can increase the amplitude of parts of the wave that are at a relatively low level, but the peaks cannot get any higher than the circuit’s maximum level. This means that as we increase the gain the peaks are in effect limited and appear to be chopped off – turning our sine into a different, more square shape.
The more we crank up the gain, the squarer our sine wave gets, creating a richer sound as extra harmonics are introduced.