A universe of distorted realities
We all know what distortion sounds like, but being able to differentiate between types of distortion is something of a dark art. Guitar processing has always revolved heavily around distortion techniques, and virtual amp software is a gateway to a world of flavours, both analogue and digital. So what’s the difference?
Fundamentally, distortion is a mismatch between your output and the original input. This ‘non-linearity’ – to use a heady term – basically means that you don’t get out what you originally put in. So in a scientific sense, any effects processor could be said to create distortion; in practice, though, distortion is a far more specific sonic process.
When a system is overloaded, audio waveforms will start to flatten at their extremes as they can’t ‘push’ any further, and this is what makes distortion occur. As the waveform flattens, harmonics are introduced. Consider the difference between a pure sine wave and a flattened square wave – because the square is flatter, it’s rich with overtones, and the same applies to any distorted signal. To see it for yourself, run a low-pass filter over a square wave while viewing the result using a spectrum analyser and an oscilloscope to study the frequencies.
The culprit could be too much voltage pushing through a vacuum tube (overdrive), a broken speaker cone that can’t move to its full extent (speaker distortion) or a digital number that can’t be represented by its output bit depth (digital clipping).
Each ‘type’ of distortion is slightly different in flavour. Some lower the resolution and cause flattened ‘steps’ in the waveform (bitcrushing), some let you graph a ‘transfer function’ to determine exactly how output relates to input (waveshaping), and some take just the topmost peaks, leaving a reducedlevel version of the original shape rather than a flat line (soft clipping).