Lexicon Aussteuerungsreserve

The headroom is the distance in dB between the Nominal Level and the Maximum Level. The purpose of this reserve is to allow room for signal peaks without causing distortion.

It depends on the type of signal how much reserve is needed. This is where the expertise of the sound engineer comes in. The Dynamics of the signal plays into this assessment. To reduce this and thus the need for headroom (compression) Dynamic Processors are used. When less headroom is needed the signal level can be increased, making the signal louder. Thus, one can buy the ability to increase signal loudness by sacrificing dynamics. This is the background of the loudness race.

Uncompressed music or speech requires 5 to 15dB of headroom, depending on the type, sometimes more. For "common dance music" a headroom requirement of 9dB was determined decades ago, it remains to be seen to what extent this applies to current music styles. On the basis of such considerations, ARD broadcasting stations apply the rule that the nominal level is 9dB below the maximum broadcast level (100% modulation). In the studio, additional headroom is also provided (another 9dB in digital installations).

For film applications, the SMTPE has even specified 20dB of headroom (between the nominal level and the maximum level at which Clipping kicks in).

For CD and for DAT, about 12dB of headroom was originally included, which is quite sufficient for a distribution medium, but somewhat tight for a recording medium. In practice, however, much less headroom is now used in order to record louder.

See also:

• Wikipedia article: headroom