Headroom is the safety margin you leave between your working signal level and the absolute ceiling at 0 dBFS. It exists because audio is full of momentary transients — a consonant, a snare hit, a door slam — that spike far above the average level, and because processing, summing, and even the DAC's reconstruction can push peaks higher than expected. Mixing with peaks around -6 dBFS gives those transients room to breathe without clipping and leaves space for mastering and for true-peak overshoot during lossy encoding. Too little headroom invites distortion; too much wastes dynamic range. Loudness normalization made generous headroom practical, since final level is set by LUFS, not peak.
