What is the difference between 0 dB and 0 dBFS

If
you use a digital audio workstation, then you come across the concepts of 0 dB and 0 dBFS a thousand times a day. Clearly you need to understand what they mean...



We
talk about differences
in sound levels in decibels.
Differences
in sound level.
So
one sound can be 10 decibels louder than another. Or you can take a sound signal and make it 10 decibels quieter. Or you can leave your fader at 0 decibels and make absolutely no change at all.
So
that is the meaning of 0 dB - no change in level.
You
cannot
say that a sound has a level of 100 dB. You cannot
do that.
When
you see something like, "The noise coming from the freeway is 100 dB", that is absolutely meaningless and written by someone who has no knowledge of decibels. (They probably mean 100 dB SPL, but that's another topic.)
0
dBFS on the other hand refers to a specific
level.
'FS'
stands for 'full scale'. 0 dBFS is the level of a signal that is at the maximum level your system can cope with without clipping the tips of the waveform.
So
-10 dBFS means a level that is 10 decibels lower than the maximum level your system can handle.
In
summary - decibels are used to describe differences or changes in level. 0 dB means 'no change'.
Values
in dBFS are used to describe signal levels in comparison with the highest level your system can handle.