Total harmonic distortion analyzer
A total harmonic distortion (THD) analyzer measures how much a sine wave is distorted. It compares the level of distortion harmonics to the level of the fundamental tone to give THD.
In practice, you test an amplifier by feeding it a very clean sine and examining the output. The THD reading includes noise and any leakage from imperfect filtering.
A common type, the fundamental-suppression analyzer, uses a notch filter to remove the fundamental frequency. What’s left—distortion products plus noise—is amplified and measured. The ratio of this remainder to the original signal is the THD. Some designs add feedback to improve how well the fundamental is rejected.
Theres also use in checking narrow-band filters, such as notch filters in parametric equalizers, to see how effective they are.
In short, the THD analyzer filters out the main sine wave and measures what remains; that leftover signal, relative to the original, is the total harmonic distortion.
This page was last edited on 3 February 2026, at 14:35 (CET).