What is peak limiting?

If the peaks on an audio waveform are already at full amplitude (0dB), any further increase in volume would result in clipping: distortion that sounds unpleasant.

It is possible to increase the power of such a waveform while avoiding distortion by using a peak limiter. Each time the amplitude of the waveform approaches 0dB (or other determined level), the gain of the peak limiter is momentarily and proportionally reduced to stop the waveform actually hitting the ceiling. Result – you can go louder without clipping distortion.