Master bus saturation
Distortion is bad… except when it’s good! Keep it subtle to sweeten brittle premasters
All analogue devices distort. Valves, transformers, inductors and tape each add their own little touches of colour, despite the best efforts of the designers. With the most renowned and desirable of these units, that colour is subjectively pleasing to the ear, very subtle, or both.
When digital recording and processing did away with these analogue artefacts, many people realised they missed them, and started to add them back in deliberately. This shouldn’t come as too much of a surprise: distortion adds extra harmonics, making the signal more complex and interesting. And as our own ears ‘distort’ in response to loud signals, distortion can help to create an impression of loudness when it’s not really there.
Complex signals like full mixes won’t sound good with the kind of full-on distortion typical of a guitar amp, however: the results will just sound a mess. For mastering, we want the type usually referred to as ‘saturation’ – very subtle and gentle, with no obvious audible distortion at all.
In fact, by adding harmonics in the upper-mid and treble ranges, saturation can sometimes counterintuitively make a signal seem cleaner, clearer and better defined. This kind of treatment is ideal when you want extra brightness, but EQ isn’t giving it to you.
However, saturation can also add thickness, warmth or density, depending on the type and levels of harmonics added; and can also help to gently round off transients, which might mean slightly more graceful behaviour from compressors or limiters downstream.
Naturally, saturation adds more harmonics than compression, so for full mix material, it’s best to use oversampling. Some plugins will require you to turn on some kind of HQ mode, whereas others have oversampling enabled by default.