FM Total Harmonic Distortion
FM total harmonic distortion is the harmonic distortion measured in a tuner's recovered FM audio, expressed as a percentage.
Harmonics are additional components at multiples of the test tone's frequency. A lower comparable percentage indicates less harmonic distortion. The result depends on reception and test conditions, so it describes more than the standalone audio output circuit.
FM Total Harmonic Distortion — Tuner
FM distortion figures belong to a specific reception mode and test signal. Mono and stereo can produce different results, as can wide and narrow intermediate-frequency bandwidth settings. Strong-signal performance does not necessarily describe reception of a weak or disturbed broadcast.
Compare the same audio test frequency, antenna signal level, mono or stereo mode and bandwidth setting. Keep limits such as 'less than' attached to the percentage. In a receiver or network music system, an amplifier or general audio-output THD figure cannot substitute for the FM tuner measurement. THD also differs from a result explicitly including noise.