dBFS — Decibels Full Scale
Definition
dBFS (decibels relative to full scale) is the level scale of a digital audio system, referenced to the largest value the system can represent. 0 dBFS is digital full scale, and every level below it is negative (−18 dBFS, −6 dBFS and so on). AES17 defines 0 dBFS as the RMS level of a sine wave whose peaks reach full scale, so a full-scale square wave reads about +3 dBFS on that scale. Unlike dBu and dBV, which refer to analogue voltages, dBFS has no fixed analogue equivalent. The alignment depends on the converter calibration, for example 0 dBu at −18 dBFS under EBU R68 or +4 dBu at −20 dBFS under SMPTE RP 155.
In the field
A common working practice keeps the average digital level around −18 to −12 dBFS, which leaves headroom for peaks up to 0 dBFS. Digital systems have no margin above full scale, whereas analogue equipment usually has headroom above its nominal level, so a signal that reaches 0 dBFS on a sample meter is likely to be clipped.
Related lessons
Sources
- DBFS (Wikipedia) : pleine échelle numérique, niveaux négatifs, définition AES17 · en.wikipedia.org
- AES Standards News Blog, « AES17 revision to clarify definition of 0 dB FS » : 0 dBFS = sinusoïde dont les crêtes atteignent le code maximal · aes.org
- Digido, « Zero dBFS Defined » : onde carrée à pleine échelle vers +3 dBFS · digido.com
- Alignment level (Wikipedia), EBU R68 : 0 dBu = −18 dBFS ; SMPTE RP 155 : +4 dBu = −20 dBFS · en.wikipedia.org