Headphone Output THD+N
Headphone output THD+N measures harmonic distortion and noise together relative to an audio test signal at the headphone output.
A smaller percentage means less combined distortion and noise under the stated conditions. Signal level, headphone load, frequency, measurement bandwidth and gain all affect the result.
Headphone Output THD+N — Headphone Amp
This measurement describes the headphone amplifier at a particular operating point. Noise can dominate at low signal levels, while distortion can rise as output approaches its limits or the load becomes more demanding. A single figure therefore cannot describe every headphone and volume setting.
Compare the same output type, load, level, frequency, gain and bandwidth, keeping any upper-limit notation. A switched tube or solid-state mode can require a separate result. THD without noise and intermodulation distortion are different measurements. The converter chip's specification or a built-in DAC's line-output result does not establish the loaded headphone output's performance.
Headphone Output THD+N — Digital Audio Player
For a player, THD+N concerns its headphone output and the supplied amplifier module, where modules are interchangeable. Single-ended and balanced outputs may have different results. The load and output level matter because the amplifier is delivering current to headphones, rather than merely feeding a line input.
Compare the same socket and amplification or gain mode with equivalent measurement conditions. If balanced connectors have different figures, keep those connector qualifications visible. An unspecified output remains uncertain. A low percentage for the DAC chip or line output cannot be carried over to the headphone socket, and THD alone omits the noise contribution.