Chris Bore wrote:
Having written at length, I reluctantly consulted Wikipedia and to my
amazement found it contained useful information.
http://en.wikipedia.org/wiki/DBFS
It does refer to the ambiguity, and in fact refers to an AES standard
(0 dBFS is rms of a full scale sine wave) and to a practial standard
(Euphonix sound level meters) that has 0 dBFS as the rms of a full
scale square wave (equivalent to the 'instantaneous' definition that I
suggested).
I find the former of these two definitions more widely used than the
latter. Any signal whose RMS value is the same as that of a full-scale
non-clipping sine wave is 0 dBFS. So a clipping square wave is
+3 dBFS.
Steve