Specs & measurements
SINAD
Also called signal-to-noise and distortion
SINAD is signal-to-noise-and-distortion ratio: how much louder a test tone is than everything the device adds to it, noise and distortion combined, in decibels. Higher is cleaner. It is the headline number on many DAC and amplifier measurements.
A SINAD of 100 dB means the unwanted content is 100 dB below the signal, far below what can be heard in normal listening. Modern DACs commonly reach 110 to 120 dB; a figure above about 90 dB is generally regarded as transparent, though where exactly audibility ends is argued.
SINAD is measured at one frequency and one level, usually 1 kHz near full output, so it is a snapshot rather than a full picture. Two devices with the same SINAD can differ in how they behave at low levels, into difficult loads or at other frequencies. Objectivist reviewers rank by it; others consider it a pass/fail gate and nothing more.
It is THD+N expressed another way: SINAD in dB is THD+N in dB with the sign flipped.