Distortion means any alternation of the original audio waveform. Usually distortion is unwanted and music producer tries to avoid it in any price. However, sometimes distortion is used as audio effect and in this case it is desirable.
Distortion we love
Distortion as a musical effect started to be used around a middle of XX century when electric guitars became popular. Today it’s hard to imagine any rock music without this effect and it is also commonly used in electronic music.
Metallica – Purify sample:
Distortion effect creates overtones by amplifying the audio signal until it gets too loud and it changes the waveform shape. Compressing the peaks of the audio signal makes the sound warmer and brighter.
Distortion turns volume variations into timbre variations and produces frequencies not originally present in the audio signal. Usually you can hear about soft and hard clipping.
In general clipping occurs when the signal exceeds the maximum dynamic range of an audio channel and top and bottom of the sound wave is cut, so this is a sort of distortion.
Soft clipping means that peaks of the output signal flatten in a gradual way and the relative amplitude of the higher odd harmonics is reduced.
Hard clipping means that audio wave is sharp where the peal is flatten and the amplitude of odd harmonics is high in the out signal.
Image credits: Wikipedia
Overdrive is kind of gain control before distortion stage meaning that it doesn’t create distortion themselves but it boost signals to levels that cause distortion on a later amplifier’s stage.
Combination of signal boosting, compression and soft clipping sometimes also is called overdrive and produces characteristically warm sound.
Distortion we avoid
Unintended clipping and distortion should be avoided by any price as any other noise that changes the original signal. For example, audio source can be too loud and the signal is going to be clipped if it is out of the gear dynamic range. Here is couple of recommendations how to avoid distortions:
- Microphone or other gear must be carefully placed to avoid that clipping.
- Using pop filter or limiter allows to stay in green at any point.
- Gain control should not be turned very high.
- In some cases you just have to remove other noise source, like bad cable.