DBFS

For other uses, see DBFS (disambiguation).
Clipping of a digital waveform. The red lines indicate full scale, and the waveform is shown before and after hard clipping (grey and black outlines respectively).

Decibels relative to full scale (dBFS or dB FS) is a unit of measurement for amplitude levels in digital systems, such as pulse-code modulation (PCM), which have a defined maximum peak level. The unit is similar to the units dBov and decibels relative to overload (dBO).[1]

The level of 0 dBFS is assigned to the maximum possible digital level.[2] For example, a signal that reaches 50% of the maximum level has a level of −6 dBFS, which is 6 dB below full scale. Conventions differ for root mean square (RMS) measurements, but all peak measurements smaller than the maximum are negative levels.

A digital signal that does not contain any samples at 0 dBFS can still clip when converted to analog form due to the signal reconstruction process interpolating between samples.[3] This can be prevented by careful digital-to-analog converter circuit design.[4] Measurements of the true inter-sample peak levels are notated as dBTP or dB TP ("decibels true peak").[5][6]

  1. ^ M. Thurston, A; H. Pearce, T; D. Higman, M; Hawksford, Malcolm (1993-01-01), Bandpass Sigma Delta A-D Conversion, Springer, pp. 259–281, ISBN 9781441951311, retrieved 2018-07-27, In all cases the reference power level used for measurements will be the overload point of the converter in question, and figures will be quoted in dBO.
  2. ^ Price, Jim. "Understanding dB". Professional Audio. Retrieved 2007-03-13.
  3. ^ Nielsen, Søren H.; Lund, Thomas. "0dBFS+ Levels in Digital Mastering" (PDF). TC Electronic A/S. Denmark. Archived from the original (PDF) on 2019-05-02. Retrieved 2018-07-27. inter-sample peaks may be considerably higher than 0dBFS.
  4. ^ Aldrich, Nika (July 2003). "Digital Distortion in CD's and DVD's: The Consequences of Traditional Digital Peak Meters" (PDF). Trillium Lane Labs. Archived from the original (PDF) on 2010-08-16. Retrieved 20 November 2010.
  5. ^ "BS.1770-4 (10/2015): Algorithms to measure audio programme loudness and true-peak audio level". International Telecommunication Union. Retrieved 2018-07-27. Meters that ... use an oversampled sampling rate of at least 192 kHz, should indicate the result in the units of dB TP [which] signifies decibels relative to 100% full scale, true-peak measurement.
  6. ^ "Terminology for Loudness and Level dBTP, LU and all that - BBC R&D". BBC. January 2011. Retrieved 2018-07-27. As can be seen from the figure, if the peak sample values are 0 dBFS, the true peak will be higher than 0 dBTP.