THD (MM)
The harmonic distortion measured through the phono stage’s moving-magnet input under stated test conditions.
THD measures harmonic distortion; THD+N also includes noise. A percentage or decibel figure is meaningful only when its metric and measurement conditions are known.
THD (MM) — Phono Preamp
For a Phono Preamp, this figure describes the MM signal path rather than the cartridge or record. Lower distortion under equivalent conditions indicates a cleaner measured output, but one test figure does not describe every listening condition.
Compare the same metric at the same frequency, signal level, gain setting and measurement bandwidth. A value marked “less than” is an upper limit, not an exact measured result. Keep any stated MM input setting with its figure.
Do not substitute the other cartridge input’s result or the distortion of an amplifier containing the phono stage. THD and THD+N are not interchangeable, and an isolated low figure does not establish how much input headroom remains.