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