[BC] Audio levels

[Richard Fry]

On May 2, 2008, at 10:51 AM, Richard Fry wrote:

> One milliwatt of audio is a standard reference level used in the
> audio and broadcast industry, and 600 ohms is a typical impedance
> used in audio signal distribution.

Abbreviated dBm ... decibels WRT one milliwatt.
___________

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.

Better to write dBmW; then there can be no doubt.  And dBk really should be 
written dBkW.  Etc, etc.

Use of capitalization also is important in writing these units, e.g., V/m 
(volts/meter) is a valid unit of measure, but V/M (volts/mega) is not.

/rant

RF