Headroom is the margin left between the current signal level and the maximum a device or digital audio system can handle. In a DAW it usually means the space between the highest peak and 0 dBFS. It is the working room that keeps later processing from clipping when the level rises.
The ceiling in digital audio
In fixed-point digital audio, 0 dBFS is the largest value that can be recorded. If your peak is at -6 dBFS, you have about 6 dB of margin measured by sample peak. True Peak can rise higher between samples, however, so check both on the final output.
Why leave margin
Summing multiple tracks, boosting a band with EQ, or making up gain after a compressor all raise the level downstream. If you run right up to the ceiling early on, you end up fixing clipping every time you change a setting.
Separate internal processing from input and output
With a DAW’s floating-point math, a bus can exceed 0 dBFS along the way and still be brought back down later. Even so, A/D conversion when recording, a plug-in’s expected input range, the final output and fixed-point files all have hard ceilings.
How it differs from dynamic range
Headroom is the margin above the current level. Dynamic range is the span between the quiet and the loud parts of a signal. Turning the output down to create margin does not restore level differences that heavy compression has already removed.
Do not treat a fixed number as the answer
Values like “always -6 dBFS” are rules of thumb; the margin needed for recording, for handing off a mix and for a final master all differ. Follow the specification you are delivering to, and if none is given, keep peaks off the ceiling. The loudness adjustment tool lets you check peak and True Peak.
