Why Specifications Matter | Part 3: Distortion

Harmonic distortion is evaluated by injecting a sine‑wave signal — typically, as here, at 1kHz — and measuring the amplitude of the harmonics generated at multiples of that frequency.

Low distortion is often a marker of quality in audio equipment. We explain how to make sense of standard distortion specifications.

The previous instalment of this series defined distortion (see Part 2), for the purpose of this treatment, as “any signal component added by elements of the signal path in response to the intended audio. In the absence of an audio input, distortion is zero.” Though there are others, two forms of distortion dominate in audio systems, and appear most often on equipment data sheets. These are harmonic distortion and intermodulation distortion.

Both forms of distortion derive from nonlinear electronic components — devices with outputs that are not strict multiples of their input — that necessarily form the core active (amplifying) circuits in audio‑signal processing blocks. These exist throughout the analogue signal path, from a microphone transducer’s or instrument’s output to the analogue‑to‑digital converter. On the reproduction and monitoring side, similar causes of distortion exist within the digital‑to‑analogue converter, mixers and other signal‑processing blocks, and monitor amplifiers.

Harmonic...