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). 0 dBFS is assigned to the maximum possible level.

There is still the potential for ambiguity with RMS amplitude measurements, since some use the RMS value of a full-scale square wave for 0 dBFS (which corresponds with a 0 dBFS peak amplitude measurement), and some use a full-scale sine wave (which corresponds with typical analog RMS measurements).

• In the case of a FS square wave = 0 dBFS, all possible dBFS measurements are negative numbers. A sine wave of larger amplitude than −3 dBFS would be clipping by this convention.
• In the case of a FS sine wave = 0 dBFS, a FS 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 derived by the equation

$\backslash mathrm\{DR\}\; =\; \backslash mathrm\{SNR\}\; =\; 20\; \backslash log\_\{10\}(2^n)\; \backslash approx\; 6.02\; \backslash cdot\; n$

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.

To make an equivalent 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.

External links

• Rane pro audio reference definition of dBFS
• Jim Price's "Understanding dB"

Digital audio