From: John Woodgate
Subject: Re: Audio noise in diff amps
Date: Thu, 19 Dec 2002 09:50:53 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Thu, 19 Dec 2002 11:59:00 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Phil Allison
wrote (in ) about 'Audio
noise in diff amps', on Thu, 19 Dec 2002:
> ** For decades the term "dBm" was used in audio for reference signal
>levels. It only rarely meant a true power level but rather a voltage level
>referred to 0.775 volts rms or 1mW at 600 ohms.
> Seems this confused some outside the club so the "dBu" was
>invented to remove the ambiguity.
No, Phil, it confused people INSIDE the club, and caused spats like you
are indulging in at present. (Do you really mean power, or just level
relative to 0.775 V?) This why 'dBu' was adopted by CCIR (later ITU-R)
and by AES in due course, even though it doesn't gel with the rules for
symbols in IEC 600027.
The r.f. people sill use 'dBm' (which should be 'dB(mW)' according to
IEC 600627, and is then *obviously* a power level). Some of them still
have to cope with reconciling levels in dBm with both 50 ohm and 75 ohm
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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