THD+N (Total Harmonic Distortion + Noise)

THD+N (Total Harmonic Distortion + Noise) measures how much an audio device alters or adds to the original signal. It’s expressed either as a percentage (e.g., 0.005%) or in dB relative to signal (e.g., -86 dB, which equals 0.005%). Lower is better.

What the numbers mean

• Below 0.001% (-100 dB) — reference tier, well below audibility threshold
• 0.005% (-86 dB) — excellent, audibly transparent for virtually all listeners
• 0.05% (-66 dB) — audible on critical listening but still clean sounding
• 0.5% and above — noticeably distorted

Reality check

Human ears can typically detect THD around 0.05% (-66 dB) on complex music. Modern budget audiophile amps and DACs achieve THD+N well below this threshold. Chasing the last -20 dB of THD is a diminishing return.

Where THD matters most

• At high output levels (near the amp’s max power)
• Under real speaker loads (not just resistive test loads)
• At frequency extremes (20 Hz and 20 kHz often show more distortion than midrange)

Budget hi-fi examples

The AIYIMA A80 measures around 0.005% THD+N at moderate power. The 3e Audio A7 with Enhanced PFFB gets it below 0.001%. Both are audibly transparent.