Lexikon Aussteuerungsreserve specifications

Category : Lexicon

The modulation reserve (engl. headroom) denotes the distance in dB between the nominal level and the maximum level. The purpose of this reserve is to give room for signal peaks without them leading to distortions.

How much reserve is required depends on the type of signal. This is where the sound engineer's expertise is needed. The dynamics of the signal plays into this assessment. In order to reduce this and thus the need for headroom (compression), dynamic processors are used. If less headroom is required, the signal level can be increased, making the signal louder. So you can buy the possibility of increasing the signal loudness by dispensing with dynamics. This is the background of the loudness race.

Uncompressed music or speech require 5 to 15dB of headroom, sometimes even more, depending on the type. For "ordinary dance music" a headroom requirement of 9dB was already determined decades ago, it is unclear to what extent this applies to current musical styles. On the basis of such considerations, the rule applies in ARD broadcasters that the nominal level 9dB is below the maximum transmission level (100% modulation). In addition, additional headroom is provided in the studio (another 9dB in digital installations).

For film applications, the SMTPE has even set 20dB headroom (between the nominal level and the maximum level at which clipping starts).

For the CD and DAT, about 12dB headroom was originally planned, which is good enough for a distribution medium, but a little scarce for a recording medium. In practice, however, much less headroom is now used in order to be able to record louder.