[BC] Audio levels

[Gordon Carter]

I really hate to disagree with Dick on this, but there is standard usage
which applies.

There are many reference materials that clearly state many standard db
usages.  One that everyone with a computer can get to is
http://www.sizes.com/units/decibel.htm

dBm -- 1 milliwatt (typically across 600 ohms, but since it is a power
reference, impedance is meaningless.  Keep in mind, though, that a
typical meter calibrated in dBm MUST be used in the proper impedance
since it is really only reading voltage)

dBW - 1 watt

dBV -- 1 volt

dBu -- .775 volt (the voltage you read with 1 dBm across 600 ohms)

dBFS -- Full scale (typically all bits on in a digital system)

There are a lot more.  Please note capitalization is VERY SIGNIFICANT in
some of these.

I was looking for a more authoritative listing but couldn't find it
quickly.

Gordon S. Carter, CPBE, CBNT
Chief Engineer
WFMT and The Radio Network
5400 North St. Louis Ave.
Chicago, IL 60625
773 279-2071

Agree that one millliwatt is the commonly assumed reference for values 
stated in "dBm," but really dBm as a standard unit is meaningless.   No
one 
can unambigously define that, as the basic measured value is not stated
(a 
watt, in this case).  It has to be inferred by the reader, and that can
be 
dangerous.  Literally read from standard SI abbreviations, dBm just
means 
decibel-milli -- which is not a measure of anything.