Dithering

When you lower an audio file's bit depth — for example from a 24-bit or 32-bit mix down to a 16-bit master for CD or distribution — the extra precision has to be rounded off. Doing this bluntly, called truncation, produces quantization distortion: a grainy, signal-correlated error that is most audible in quiet fades and reverb tails. Dithering adds a low-level random noise before the rounding, which decorrelates that error and turns it into a smooth, benign hiss the ear ignores rather than an ugly artifact. Optional noise shaping pushes the dither energy into frequencies where hearing is least sensitive. Apply dither only once, as the very last step of your final export, and never to a file you plan to process further.