Channel Summing

[cgk-37090]

Can anyone explain it? And is +3Db consistent on every board in the industry?

Thanks

[vulcan_dc]

Hello,

i hope u can find your answer here.... http://www.3daudioinc.com/3db/forumdisplay.php?f=15

and are u talking about the pan law with most boards??...

HTH
cheers..

[cgk-37090]

I am referring to the rule where every time you double the number of channels for a mix you need to account for +3Db. Meaning if you have 2 singers, each channel (individualy) should be set for -6Db on the main meters, then when you bring up both channels they should be at zero or unity, if the gain structure is set up correctley. I am wondering if the +3Db is a standard on all boards. Also this is on an analog board...is there a diiference on a digital board?

Thanks

[vulcan_dc]

ah... sorry mate... just noticed this thread was in FOH forum.... the link i put in on my last post was about DAW sum comparision ...:o :p :) ... sorry about that... ;)

[sabianq]

while it is true, that mixers sum, the final master summation is actually an average of the total gain.

this works in active mixers. in passive mixers, the total gain drop can be stated by a mathematical rule (I don't know off of the top of my head) then you need a preamp to bring the final gain to your working level a gain, (one reason passive mixers have a loud noise floor)

in general, most console mixers (now days anyway) are active mixers and do not have the problems associated with gain drops.

[cgk-37090]

Well, here is where I am coming from:

If I have 4 channels, and I bring eack channel up to zero on the main level meter individully to set my gain for that channel, when I bring all 4 up at the same time I will be well over zero on my main level meter. I have heard that with channel summing every time you double that number of channels you need to subtract 3Db. Then when you set your gain, all channels should at zero should be at zero on the mains.

[sabianq]

I think I just figured out what you are talking about

are you talking about the -3 db gain before feed back per mic when you have multiple open mic's in a live sound situation myth?

If you are, then yes, there is a linear -nth db drop added for every microphone you have open. and that can work out to around 3 db depending on your setup and manufacture of gear.

but if you are asking if this is the same for every board, the answer is no as the the circuitry in the console, amplifier, and other electronics you have in the chain greatly dictates the gain before feed back. some cheap mixers are very susceptible to feed back while some high end mixers are relatively immune to feedback.
I refer to some of the lower end mixers as being "loose"

another thing to realize is that if you use dynamic microphones, the gain before feedback can be higher than if you use condenser microphones.
so the answer to your question is actually, "no" there are many different things that affect your gain before feedback tolerance numbers.

I hope this helps.



feed back can also be attenuated by removing offending freq's with an eq.