"Don Pearce" wrote in message
...
On Sat, 18 Mar 2006 17:54:15 GMT, "don" wrote:

dbm is as stated a reference of two like power values to a 1mW reference
however the impedence does not need to be 600 ohms, it can be any value
of
ohms as long as both power values are based on the same impedence


Don,

Do you have a reference for this statement? In 34 years in Pro-Audio I have
never heard it expressed in this way, always referred to 1mW into 600 ohms.



dBu is indeed dB (unloaded). It is a relic of 600 ohm line audio
systems and is the voltage that would have produced 0dBm in 600 ohms,
but since we now run into high impedances instead, must be specified
otherwise - hence dBu.

dbv would be a ratio based on two voltage levels and a reference of 1 volt

dBV, actually, not dBv.


this is treated the same as voltag calculations because it is based on the
signal to noise ratio.

It has nothing to do with signal to noise ratio - it is all happening
at the other end of the scale.

I have no diea what the above is referring to: dBFS has nothing to do with
signal-to-noise, it is just how many dB below full-scale.

S.