tonistry.

Specs & measurements

THD+N

Also called total harmonic distortion plus noise

THD+N is total harmonic distortion plus noise: everything a device adds to a test tone, distortion and background noise together, as a percentage of the signal. It is the figure most spec sheets quote and the inverse of SINAD.

0 dB−40−80−120noise1 kHz2345tone removedharmonicsTHD+N 0.001%−100 dB, SINAD 100 dB
To measure THD+N the analyser removes the test tone and measures everything left: the harmonics and the background noise together, as a share of the signal. A THD+N of 0.001 percent is −100 dB, a SINAD of 100 dB.

Adding noise to THD makes the figure more honest for quiet signals, where hiss can dominate. A specification such as "0.001% THD+N at 1 kHz, 1 W" tells you the level and frequency it was measured at, which matter: distortion rises as an Amplifier approaches its limits.

Converting to decibels gives SINAD: 0.001 percent is −100 dB, so a SINAD of 100 dB.

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