[Elecraft] OT: "Line level"

[Jim Brown]

I believe you may be confusing voltage levels with impedance.  600 ohms 
has NOTHING to do with it beyond defining the voltage present in a circuit 
where levels are defined in dBm.  dBm means dB with respect to 1 mW, 
where the impedance must also be defined. dBu, the current most 
common reference in pro audio, is defined as the voltage with respect to 
0.78 volts, independent of the circuit impedance. Of course, 0.78V  
corresponds to 0 dBm in 600 ohms. 

There are also issues about how digital guys think about level and how 
analog guys think about level. Digital folks tend to think of absolute 
maximum peak levels -- all the bits on, digital clip. This corresponds 
roughly to 100% modulation of an AM transmitter. But audio levels are 
DEFINED as the RMS value of a waveform. That 13 dB difference you are 
talking about is the approximate difference between RMS and peak of an 
uncompressed audio waveform. Both ways of thinking/talking about it are 
important, but you absolutely must understand the difference. 

Jim Brown K9YC
http://audiosystemsgroup.com

--Original Message Text---
From: G3VVT at aol.com
Date: Fri, 2 Jul 2004 07:30:49 EDT

600 ohms is still very much the standard.