[BC] Audio levels

[Peter Smerdon]

Gordon's reference seems audio-centric, so it is only half the story.

The confusion is one of context (and difficulties with plain ASCII text)

The unit dBu which equals 0.774V rms is for audio (where u="unterminated").
The unit dBu which equals 1 microVolt is for RF Field Intensity etc. 
(where u = a rough way to infer lowercase "mu")

You just have to look at the context to figure out whether the author 
meant dBu or dB"mu".

Still, wouldn't it be nice if the RF people who write dBu for dB wrt 1 
microVolt would use the extended character set (when available) to pull 
up the "mu" character and use that.

All the references I've seen are either from an audio or from an RF 
perspective. Haven't seen one which covers both disciplines.

One I've just pulled up which is RF-centric is
http://engr.nmsu.edu/~etti/fall96/communications/db/db.html



Gordon Carter wrote:
> 
> 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)
> 
>---snip----
> 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
> 

Cheers!

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Peter Smerdon.

Radio 3mp - Melbourne's Easy Music
sen-1116  - Melbourne's Home of Sport

Melbourne, Australia.
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