Distortion is by far the most loved and used effect in modern music. It is prominent in rock, metal, and dance, as well as almost every other genre to some degree. It is easy to identify and rich in sound. Very few instruments will find no use for distortion in one way or other. Originally a setback and issue in analogue equipment, musicians discovered it can be used very musically for a much warmer, rougher sound, rich in harmonics. Whole genres have been formed and pioneered from this one effect and its ease of use means anyone with any level of music understanding can use it.
So what is distortion and how can we use it? Here is a brief description of it. But in short, it is the physical limitations of circuits, trying to handle a signal that is too high. What happens is the waves get squared off at the top creating rich harmonics not present in the original signal.
Originally exclusive to tube amps and inadequate sound gear, there are now many, many hardware and software methods to creating distortion. Guitar effects pedals may be the most familiar hardware, where the pedal is inserted between the guitar and amp. They can create gentle over-driven tones to spine-chilling distortions that could give a black metal guitarist goose-bumps.
So what are some creative uses of distortion? Well, the first and most obvious is aggression. Rock and metal music have formed around this sound, combining it with aggressive chords to auralise their emotion.
The high harmonic content adds a lot of energy to the sound, great for choruses where a clean signal suddenly goes into overdrive, driving the energy of the music through the roof.
Its sound can be comparable to the rough nature of engines and is not a sound that occurs in nature, making it sound very human and interesting.
One creative use of distortion is to start with a clean signal and duplicate it. Add distortion to one and leave the other unaffected. Start with the volume all the way down on the distorted signal with the clean signal all the way up.
As the section progresses slowly cross-fade towards prominence on the distorted track to gradually increase the grit and energy of the sound as it builds towards a more energetic point. How abrupt this cross-fade happens depends on how sudden you want the energy to change.
Depending on the song a quick switch may be preferable or, you could want a very long transition potentially lasting minutes. Of course, if you have a more advanced distortion effect or VST, it may incorporate a Dry/Wet or a Mix knob.
Another trick, as described here, is to use the distortion as a compressor. Now this is probably going to ring alarm bells in some people as we like our compression to be as transparent as possible but hear me out.
As distortion is squaring off the top of the waveforms, it means they are as loud as they can go. This reduces the volume of the highest peaks (or any above the distortion threshold) to that threshold. It is essentially a limiter.
Now, of course, you can hear this in a very obvious way and you wouldn't want to compress your clean vocal mix with distortion. But if you have an instrument or sound that you feel needs tamed volume-wise and at the same time, it needs more grit, distortion is the way to go.
If you have a nice sub-bass or even bass guitar, most of its frequencies are very low down. By adding gentle distortion you get "warmth" which can be very desirable to the aesthetic of the sound. It also allows the bass to be audible via the harmonics on systems that cannot reproduce low frequencies.
Not everyone is well kitted out for bass.
Likewise, if you have a dull sound, and you feel it could be a bit brighter, add a small amount of distortion and a high shelf boost on the higher frequencies and there should be some nice harmonics brought out. Lots of frequency exciters work on a similar principle.
There are bad types of distortion, e.g speaker distortion which sound bad. Speaker distortion happens when the signal is too high for the speakers to handle but even that can be used creatively in mind.
Of course, you don't want to actually distort speaker cones, at risk of breaking them but, if you want to emphasise the volume of an explosion, you could add some low-frequency distortion.
This tricks us into thinking the sound is much louder as we can "hear" the speakers straining. This is a trick used in cinema and depending on the sound engineer can be either subtle, or not so much.
Finally, distortion can be used in the mixing and mastering process to emulate the sound of old analogue tape recording. By adding some tape distortion, it very softly colours the low end, as tape did back then and gives it a more vintage feel to the track. There is a brilliant Free Plugin that does that well, called Ferric TDS.