balanced line measurments

I just had to measure the audio voltage on a balanced line and suddenly wondered how do you do that???

I guess I am so used to measure one line to the ground reference.

I did measure the signal between the two lines and left the shield alone, but I just wanted to ask the question to make sure I didn't make a silly mistake.

Uwe

You could use a scope in differential mode - one input on each line, and the ground to shield.

Yeah, but the question is what do I measure.

If a line amplifier calls for a certain output level, by what method should that be determined. My scope is not the most precise device for measuring voltages, for that I do prefer my HP AC RMS voltage meter

Uwe