Distortion

Distortion is anything that effects a signal. Anything that adds or removes from it. In terms of production it is often used to describe the deliberate manipulation of the signal to produce an audible effect.

In analogue circuits, and overloaded circuit means the signal's waveform is squashed at higher levels. When a wave distorted in this way its harmonic content changes, with overtones often including harmonics added. Digital distortion simulates this effect.

Types of Distortion

• Type 1: Linear, altered amplitude. AKA Frequency response also includes phase errors (parts of the signal going out of phase with one-another).
• Type 2: Nonlinear, added frequency content.

Type 1

• Linear Distortion: When all audible frequencies are transfered at the same level a system is linear. If frequencies are output at different levels, the signal is distorted. The wider the effected band, the easier the distortion is to perceive.
• Bandwidth Distortion: Falloff at the high or low end of the response that is more than 3dB.

Type 2

• Harmonic Distortion: Either symmetrical (odd order) or asymmetrical (even order). Lower (2nd, 3rd, 4th) harmonics are less audible as distortion. Higher order harmonics are much more prominent.
• Intermodulation Distortion: Interaction between two frequencies creates new frequencies that are the sum and difference of the two frequencies. These are unrelated and highly dissonant frequencies and therefore more audible at low levels than harmonics.

Saturation

Saturation is a flaw in the accuracy of magnetic tape when used for recording audio. Once a signal reaches a certain point, the tape cannot record any more signal - it has become saturated. However unlike digital recording which clips, this process is more gradual and unpredictable. When saturation begins to occur, the signal is distorted and compressed in a non-linear way, with signal level, dynamic range and frequency being changed. This effect is often pleasing to the ear.