# Use of plus 4/minus 10 (+4/-10) switches?



## Anonymous067 (Aug 30, 2008)

When using audio gear, how do I know which to set all my gear to.
When I bring my IEM system into a venue and want to hook it up to their aux send off the board, which switch SHOULD it be on?
I know its a different measuring system but it has always confused me.

Explain?


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## waynehoskins (Aug 30, 2008)

It's signal level. Pro gear operates at +4 dBu (is it dBu? dBsomething); consumer line-level gear operates at -10 dBsomething.

So if you're interfacing to pro gear, you probably want it at +4; if consumer, -10. If you hit a consumer piece of gear with a +4 signal, that's +14dB to it, so you're hard clipping its input stages. If you hit pro gear with a -10 signal, it's weak (-14 dB), so you have to crank it.


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## mbenonis (Aug 30, 2008)

Almost. 

I was working through the math of this the other night for a project. +4dBu is a voltage signal, referenced to 0.775 V. Thus, 4 dBu is actually 1.228V. (4 = 20*log(V/0.775); thus 0.2 = log(V/.775) and V = 0.775*(10^0.2))

-10 dBV is also a voltage signal, but referenced to 1V. So this signal would be 316 mV (-10 = 20*log(V/1); thus -0.5 = log(V) and V = 10^-0.5 = 0.316).

Thus, the difference in voltage would be: V = 20*log(1.228/0.316) = 11.79, or approximately 12 dB difference in signal strength.

THe short answer to your question is that almost all consoles reference their outputs to 4dBu, unless noted. Most IEM gear will probably have a switch on it. So just set the switch to +4 dBu and plug it up.


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## waynehoskins (Aug 30, 2008)

mbenonis said:


> Almost.
> 
> I was working through the math of this the other night for a project. +4dBu is a voltage signal, referenced to 0.775 V. Thus, 4 dBu is actually 1.228V. (4 = 20*log(V/0.775); thus 0.2 = log(V/.775) and V = 0.775*(10^0.2))
> 
> ...



I couldn't remember if they were referenced the same or not, and I was too lazy to check. Well done.


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## howlingwolf487 (Aug 30, 2008)

You'll also want to look up the venue's console(s) in advance to see if the Aux Sends, etc. actually are pro line level (+4dBu). I think Allen Heath's consoles have differing levels from Main Outs to Aux Sends.

Either way, read up on the gear if you're not sure (and if you know what's coming up). I always try to advance the gig, no matter how big or small it may be. It makes EVERYTHING go more smoothly and sometimes can clue you in to good reasons not to take a gig.

Best of luck!


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