Harmonic Distortion
Definition
Distortion that adds harmonic overtones, multiples of the original frequency, to an audio signal. Even-order harmonics (2nd, 4th) are typically perceived as warm and musical; odd-order harmonics (3rd, 5th) can sound harsh and abrasive at higher amounts.
In Simple Terms
Extra tones added to a sound by equipment or plugins, some warm and pleasant (even harmonics from tubes), some harsh and aggressive (odd harmonics from transistors). It's the secret ingredient behind that "analog warmth" people love.
In Practice
A tube preamp driven gently adds predominantly 2nd-order harmonic distortion to a vocal, giving it warmth and presence. A transistor circuit clipping hard adds odd-order harmonics, which sound harder and more aggressive.
Common Confusion
"Even harmonics = good, odd harmonics = bad" is too simple. Both types are present in nearly every analog circuit; the perceived character depends on relative amplitude and the source signal. Many beloved analog units (Pultecs, 1176s, Neve preamps) generate a specific blend of both, naming a unit "even-harmonic-only" is marketing more often than physics.
Sources & Verification
- Pakarinen, J. & Yeh, D. T.. A Review of Digital Techniques for Modeling Vacuum-Tube Guitar AmplifiersComputer Music Journal, 2009
- Hamm, R. O.. Tubes Versus Transistors. Is There an Audible Difference?Journal of the Audio Engineering Society, 1973
Last verified: 2026-05-05