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G G G Gain Structure!!!!!! Argg!

John SJohn S Posts: 29
OK, before I begin, I let you know that I spent about 5 hours reading the posts on this AND the archive board. I see alot of info. Some of it seems contradictory, but it all makes sense. For instance, some of the articles say to \"always max out the channel trim levels\" and some say to keep them 3db below clip.

First, my basic setup:

2 x SR4733a mains - EACH powered by a mono-bridged QSC2450
2 x SRX728s subs - EACH powered by a mono-bridged QSC3602
Mackie CFX16 board & misc. insert comps and eqs.

I just got the 260 last week and have read everything I can get my hands on. In the READ ME first section of the board, the long article on setting gain structure is very helpful, but a few things I don't understand, as follows:

1. Run pink noise through the board's channel --- OK, I downloaded the pink noise file into my IPOD and will connect it to channel 1. The gain coming from the IPOD is obviously different than the gain coming from the SM58 that I will have in that channel when the band plays. If I set my gain structure with the IPOD, won't EVERYTHING change once I introduce a new audio source to that channel (like a mic)??? At least, won't the channel trim settings be drastically different?

2. If I use the Wizard to set up, it tells me that my 2450 amps need to be set at about 37% and the 3602 amps at about 41%. So which setting do I leave them at --- the setting I do when I set my gain structure or the setting the Wizard tells me to set them at??? (For this question, I also assume that the order I should go in is 1. Set gain structure, 2. Auto EQ, 3. Sound check the band) --- I'm not sure exactly what step I should be going through the setup wizard I guess.

3. Should I always be shooting to have EVERYTHING in the system operating at O db (unity). For instance, my board doesn't show clipping until the signal reaches +22db.

I have a few more questions I'll pose when I have a few more minutes. Thanks in advance.


  • DraDra Posts: 3,777
    #1 - This proccess is for setting the board's output through the 260 to the amps only. The pink noise maxed out simulates all channels going to the mains. The individual channels must be set using PFL each time as the channel and source are changed.

    #2 - Ideally, do the gain set-up, take 1 top and one sub outside to do the EQ session. Then balance the system (1 top / 1 sub) by turning down the louder speaker amp while listening to a good CD. This means that 1 amp stays where it was from setting the structure and the other turns down to the balancing point. Match the unused amps. Now when auto EQing take the data from the gragh and \"apply\" it to the output PEQ's to flatten everything. Repeat until you are pretty happy. Then redo the gain structure, rebalance, re-check the auto EQ. You will know you are done when you are balanced and flat on the Auto-EQ gragh and no amps clipping. Of coarse you know from reading that Auto-EQing is hazardous indoors, except as spelled out within certain limitspecified. (All this by the way is in the RMF and in hundreds of posts)

    #3 - Ideally, each channel is giving unity (-0-) to the main bus(s?). The mains conrol the mix output level. If that means running in the yellows or -9db, so be it. Mixing style and content does play a roll, but in general -0- is the normal.

    I agree that some of the info is contradictory, but there are no absolutes, only guidelines.


  • John SJohn S Posts: 29
    Thanks. That does clear up a lot. So, (knowing it's only a generality) when I'm doing a rock show, I generally don't want the mains on my board to go above 0 db on the output meters? The rest of the gain on my board up to +22 db is all just for additional headroom and gear protection? Yes...I know it's a complete newbie question but I'm absorbing alot quickly.
  • GadgetGadget Posts: 4,915
    No sir...that means that when you set the gain structure you start with the input channel strips.... there are (X) number of them and only 2 masters... so to get optimum signal to noise on the board... set the individual channel faders in the 'design center' that place that corresponds to '0' on the scale (about 3/4's of the way up). (proper mixing technique then has those MOST important items ... like vocals @ -0- and the lesser items pulled down corresponding to their place in the mix)Then press the PFL button and use the master meter to set the channel strip input gain to at least \"average\" -0- vu or slightly more...but NEVER clip or even close...Then send a signal equal to just below the clip threshold of the mixer (red lights JUST tickling) then, set the 260 input and output levels but they need to be a bit lower so no digital clipping could EVER happen...then set the amps to just clip and turn them down slightly lower... the thing here is that the ONLY thing @ clipping is the mixer...and the 260 is well below that, and the amps are as well..this way we KNOW that when the mixer is at almost clipping, the rest of the system is as well...but just below...

    As far as the output meters, if you can get full concert volume with no more than a -0- vu meter level...you have 22-28 db of headroom which is EXCELLENT! However, as long as you have 8-10 db your fine...

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