What is “dither” with respect to analog-to-digital converters?

In analog-to-digital (A/D) conversion, quantization noise occurs because an infinite number of analog values must be mapped to a limited number of digital steps. When measuring very small, repetitive signals, this creates predictable, distortion-causing errors known as harmonic distortion. To combat this, engineers use 'dither' by intentionally adding a small amount of random white noise to the analog signal before conversion. This randomizes the quantization steps, breaking up the harmonic distortion and replacing it with a steady, low-level noise floor that is much easier on the ear or processing system. While adding noise sounds counterintuitive, it actually improves the dynamic range of the converter. Distractors suggesting dither is an error condition or a method of decimation mistakenly frame it as a flaw or a sampling reduction technique rather than a deliberate enhancement.