DBFS

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The correct title of this article is dBFS. The initial letter is shown capitalized due to technical restrictions.

dBFS means "decibels full scale". It is an abbreviation for decibel amplitude levels in digital systems which have a maximum available level (like PCM encoding).

Clipping of a digital waveform.
Clipping of a digital waveform.

0 dBFS is assigned to the maximum possible level.[1]

There is a potential for ambiguity when assigning a level on the dBFS scale to a waveform rather than to a specific amplitude, since some derive the characteristic level of the waveform from its peak amplitude value, while others use its RMS amplitude value.[2][3][4]

  • For the case in which the RMS value of a full-scale square wave is designated 0 dBFS, all possible dBFS measurements are negative numbers. A sine wave could not exist at a larger amplitude than −3 dBFS without clipping, by this convention.
  • For the case in which the RMS value of a full-scale sine wave is designated 0 dBFS, a full-scale square wave would be at +3 dBFS.

The measured dynamic range of a digital system is the ratio of the full scale signal level to the RMS noise floor. The theoretical dynamic range of a digital system is often estimated by the equation

\mathrm{DR} = \mathrm{SNR} = 20 \log_{10}(2^n) \approx 6.02 \cdot n \,

This comes from a model of quantization noise equivalent to a uniform random fluctuation between two neighboring quantization levels. For instance, 16-bit audio has a quoted dynamic range of 96.33 dB.[1]

To make an equivalent RMS measurement of a system's noise floor, the full-scale square wave convention is used. A signal which fluctuates randomly between two neighboring quantization levels will measure at −96.33 dBFS with this convention.

[edit] References

  1. ^ a b Price, Jim. Understanding dB. Professional Audio. Retrieved on 2007-03-13.
  2. ^ Decibel - Voltage ratios for electric signals. sizes.com. Retrieved on 2007-03-13.
  3. ^ RMS Settings (PDF). Adobe Audition - User Guide for Windows. Adobe (2003). Retrieved on 2007-03-16.
  4. ^ 0 Db Reference. Active Voice / Noice Level Monitor User's Guide. GL Communications, Inc.. Retrieved on 2007-03-16.

[edit] External links

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