Signal Processing
What Is Distortion in Audio?
Quick answer
What distortion means technically
In technical terms, distortion means any change to the shape of an audio waveform that wasn't in the original signal. The input goes in; the output comes out different. The difference between them — whatever was added or modified — is distortion.
By this broad definition, even a microphone with imperfect frequency response introduces distortion. In practice, "distortion" usually refers specifically to nonlinear distortion — where the circuit or process doesn't handle all signal levels uniformly, causing the output to deviate from a clean amplification of the input.
Types of distortion
| Type | Origin | Character | Intentional? |
|---|---|---|---|
| Hard digital clipping | Signal exceeds 0 dBFS; waveform cut flat | Harsh, buzzy, unpleasant | Rarely — usually a recording mistake |
| Soft clipping | Gradual saturation, rounded peaks | Warmer, more musical than hard clipping | Often — tube amp emulation, saturation plugins |
| Tape saturation | Magnetic tape overloading at high levels | Warm, harmonically rich, slight compression | Very common — adds "analog warmth" |
| Overdrive | Moderate gain applied to guitar amp or pedal | Growl, sustain, added harmonics | Yes — fundamental to rock and blues guitar |
| Fuzz / heavy distortion | Extreme clipping, often waveform squared off | Aggressive, sustaining, wall of sound | Yes — stylistic effect |
| Intermodulation (IM) | Multiple frequencies distorting together, creating sum/difference tones | Muddy, inharmonic, unpleasant | Almost never — a sign of poor equipment |
Why some distortion sounds musical
When a signal is distorted, new frequencies are added to the output. These are called harmonics — multiples of the original frequency. A note at 440 Hz (A4) might generate harmonics at 880 Hz, 1320 Hz, 1760 Hz, and so on.
Even harmonics (2nd, 4th, 6th) are musically related to the original note — they're the octave, the double octave. Tube amplifiers and tape saturation tend to generate primarily even harmonics, which is why they sound "warm" rather than harsh. The added harmonics feel musically integrated.
Odd harmonics (3rd, 5th, 7th) are less musically related — they're the fifth, the third, the seventh in a way that clashes rather than blends. Hard digital clipping generates a mix of odd and even harmonics with a strong odd-harmonic component, which is why it sounds harsh and unpleasant.
Total Harmonic Distortion (THD)
THD is a measurement of how much harmonic content a piece of audio equipment adds to a signal. It's expressed as a percentage — the ratio of harmonic content to the original signal. A microphone preamp specified at 0.001% THD adds an extremely small amount of distortion; a guitar amp running into clipping might add 20% or more.
For transparent, studio-quality equipment, THD below 0.01% is generally inaudible. For intentional character (tube preamps, analog tape), higher THD is a feature, not a bug — it's what gives the equipment its sonic personality.
Distortion and audio conversion
Lossy audio codecs don't add classic distortion — they use psychoacoustic compression rather than waveform clipping. However, at very low bitrates they introduce their own form of spectral distortion: the smearing and artifact sounds that emerge when the encoder makes poor decisions about what to discard.
The important distinction: if audio already contains intentional distortion (guitar overdrive, tape saturation), that's baked into the signal before encoding. The codec treats it like any other audio content. If you're encoding a distorted guitar at 192 kbps MP3, the encoded file will faithfully reproduce the distortion — it was always just audio data.
Last updated: March 28, 2026