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26th March 2012
#1
Gear interested

Line reference level explanation

Hi everybody!

I am musician and have been playing for already 20 years now. Even though I have always been into home recording, I have just started to get seriously into it.

I have always thought I had the basics quite clear but I just found out that there is one think that wasn't that clear to me...

My question is all about signal reference level. According to its formula, the dB is calculated as the relation between a measured signal level and a reference level:

dB = 20 X log (Measured level / Reference level)

So far, my take on this was that when my console's VU meter was reading 0VU, then the output voltage would be 1.23 Volt or 0.316 Volt respectively when +4dBu or-10 dBV where selected:

Reference level : +4dBu : 1.23 Volts
20Xlog (1.23/1.23) = 0 dB

Reference level : -10dBV : 0.316 Volts
20Xlog (0.316/0.316) = 0 dB

However, when I gave it a thought, I realised that this cannot be possible as if I come to use the above formulas as I did, I'd actually be changing the dB scales. They will not be dBu nor dBV anymore, as these two scales respectively have 0.775 volt and 1 volt as reference values:

Reference level : dBu : 0.775 Volts

Reference level : dBV : 1 Volts

This makes me doubt, as then 0VU reading on my console would be indicating 0.775 or 1 volt output levels instead.......

Would anybody please give me some light on this???? what is the role those values are playing into the whole thing?

26th March 2012
#2
Lives for gear
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You can measure exactly what your console is putting out with a Vac voltmeter and sine wave tone, across the balanced + and - pins.

Professional VU meters are normally 0 VU = +4 dBu = 1.228V, but there's no reason to expect it to be cal'd this way in your system--especially with consumer analog gear that does not have a high max level, it might be cal'd to 0 dBu to give more headroom in the system.

It also obviously depends on where the -10 dBV selector is in the signal path. It might not be before the VU meter, and instead is right on the output. Therefore, to get 0 VU you still need to hit +4 dBu, but that's not what you measure out of the desk.
27th March 2012
#3
Gear maniac

What does your console's manual have to say about that? It should tell you what the console's nominal operating level is (0VU = +4 or 0 dBu or -10 dBV)
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