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Connecting Mixing Boards
Old 1 week ago
  #1
Here for the gear
 

Connecting Mixing Boards

I play in a band that uses a Soundcraft UI24R. We run our own sound with our own PA system and our own sound tech 99% of the time but every once in a while we will book something that has sound provided. It never fails that every time we book these jobs the guy running sound sucks. Therefore we want to use our own sound guy. The problem with this is that with all of the different boards out there it kind of makes it difficult to know how to run all of them especially the ones like ours where everything is digital so having our sound guy run everyones systems isnt feasible. So at our last gig that had provided sound, we decided to try something different and run through our board so we could take advantage of our in ears and simply run the left and right main outs to the 1st and 2nd channel of the venues mixer. This way our sound guy could run our system for the mix as he is familiar with our board and the venue would just have control of the master volume. The first time we played this venue our sound was horrific. The second time we ran it our way with our sound guy it was one of the best sounding nights we've had. So the question is, what problems or issues could we have and is this the correct way to do this? Bottom line, we want to run our mixer with our sound guy using our mixer but take advantage of the house PA when sound is provided. Spec wise the max main output for the UI24r is 20.5dbu and headphones Is 500mw. When we ran using this method, we pulled our main output all the way down on our board, had the venue give us about 50% on channel 1 & 2 slider and main out on their mixer, then we started pulling our main output volume up on our mixer until the volume was good and we weren't clipping.
Old 1 week ago
  #2
Here for the gear
 

Been there done that, and as long as you get the gain right into the house board you are golden. We run our own sound and know it ever so well. Every local cabaret we play that has a house sound guy doesn't understand what we need and so we just feed him a L/R main out and buy him a few beers.

Success!
Old 1 week ago
  #3
Gear Nut
 

Quote:
Originally Posted by Swfullback22 View Post
I play in a band that uses a Soundcraft UI24R. We run our own sound with our own PA system and our own sound tech 99% of the time but every once in a while we will book something that has sound provided. It never fails that every time we book these jobs the guy running sound sucks. Therefore we want to use our own sound guy. The problem with this is that with all of the different boards out there it kind of makes it difficult to know how to run all of them especially the ones like ours where everything is digital so having our sound guy run everyones systems isnt feasible. So at our last gig that had provided sound, we decided to try something different and run through our board so we could take advantage of our in ears and simply run the left and right main outs to the 1st and 2nd channel of the venues mixer. This way our sound guy could run our system for the mix as he is familiar with our board and the venue would just have control of the master volume. The first time we played this venue our sound was horrific. The second time we ran it our way with our sound guy it was one of the best sounding nights we've had. So the question is, what problems or issues could we have and is this the correct way to do this? Bottom line, we want to run our mixer with our sound guy using our mixer but take advantage of the house PA when sound is provided. Spec wise the max main output for the UI24r is 20.5dbu and headphones Is 500mw. When we ran using this method, we pulled our main output all the way down on our board, had the venue give us about 50% on channel 1 & 2 slider and main out on their mixer, then we started pulling our main output volume up on our mixer until the volume was good and we weren't clipping.
If your main output on your mixer was far under 0db/unity/ whatever reference output is then that could be an issue.

Issues.

1. A mistake on your end could increase the signal 20db. lol, yikes.

2. You never want to squash a line level signal down just to increase it later


For best signal/noise ratio you want to send a line level/reference level to FoH, then FoH can pad the input down.

If FoH for some reason doesn't have a pad you want to use a passive XLR pad to lower the line level down. The UI24 mixer has self noise, the mic pres have self noise, by lowering the UI24 master level down, then having FoH boost the level up you are also boosting all the hum, crackle, and hiss back up by the same amount as the music, that means you could be adding 20-40db of noise to the feed your sending FoH.

Simple answer is carry some xlr pads to pad your signal or have FoH pad it.
Using XLR pads will eliminate the chance of FoH messing anything up during the show level wise/pad wise.

It's better, IMO, to send out a line level signal and pad it down 20db before the FoH, then to send out a signal 20db to low and have FoH gain it up. That's 20 db of noise your adding into the signal.

Passive pads should not add any noise into the system.

At least this is what has worked for me.
Old 1 week ago
  #4
Here for the gear
 

So if I'm reading this correctly, you would keep the main output from the UI24R hotter going to the venue mixer then pad it? Then the house mixer would increase the overall volume without getting noise?
Old 1 week ago
  #5
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Also, what is the risk of damaging the FOH mixer if we did accidentally turn up the main out from the UI24R? Would it damage their board or burn the channel out?
Old 1 week ago
  #6
Here for the gear
 

Agreed that we typically sent the house mixer a 0 VU/Unity gain signal so he can set unity gain throughout the signal path. This improves S/N ratio and avoids driving his input too hard later.
Old 1 week ago
  #7
Here for the gear
 

So how do you know its 0db? The max we can send is 20.5db and that's everything all the way up which we obviously dont run. So if I pad it 20db then wouldnt they be getting a negative Db?
Old 1 week ago
  #8
Gear Nut
 

Quote:
Originally Posted by Swfullback22 View Post
So how do you know its 0db? The max we can send is 20.5db and that's everything all the way up which we obviously dont run. So if I pad it 20db then wouldnt they be getting a negative Db?
Here is where things get a little tricky with different boards, analog vs digital, etc.

So the "20.5db" you listed isn't the real spec, here are the real specs. the unit of measurement is actually "DBu" not "db"

"Mix output +20.5dBu max"

Notice it says "max" output, this give you an idea of how much dynamic range you have.

I looked for the specs for the "nominal operating level" of the UI24r mixer but I didn't see any listed in the owners manual. However every other modern soundcraft I have used/read up on operates at "0DBu" level.

ODBu operating level is the output level most of the music will be at, then loud parts will jump up to around 20Dbu, this gives you 20DBu of headroom before you get distortion.

I looked at the owners manual for the UI24 but the photos were Superbad and I couldn't tell how SC displays levels...

OK, so it looks like SC lists "0" on the VU meter as peak, then comes red/clipping, this would be the same as the DBFS scale where "0dbfs" is the max you can reach.

Sorry the answer is so long, lol.
So if your scale tops out at "0" then normal music level should be around "-20", but you aren't lowering the level -20, your allowing the needed 20DBu of headroom that there is in most live music.

If your mixer is "0Dbu" level, which I bet it is, that is actually better for you, in this situation since the output is already padded, or 4DBu lower then pro level output.

P
Attached Thumbnails
Connecting Mixing Boards-analog_digital_and_acoustical_scaling_in_loudspeakers3.gif  
Old 1 week ago
  #9
Gear Nut
 

Quote:
Originally Posted by Swfullback22 View Post
Also, what is the risk of damaging the FOH mixer if we did accidentally turn up the main out from the UI24R? Would it damage their board or burn the channel out?
It would cause massive distortion and could fry the speakers.

It could cause a massive jump in loudness and ruin the show
Old 1 week ago
  #10
Lives for gear
 

use an external mix matrix/speaker processors with multiple i/o's: any desks feeds into this unit which connects to your pa.

of course analog i/o's of the processor and the pa need to be matched (in dBu), meaning the max. output before clipping of the processor needs to be the same as the pa's input: if the latter cannot take in the same amount of level, it needs to be padded down: use external attenuators (or the amp's input gain) - however, there are still plenty of options to overdrive the system...
Old 6 days ago
  #11
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Pro Sound Guy's Avatar
 

Run the input gains and output normal on the UI24R for good gain structure.

Use the main physical R/L outputs on the front of the Ui24R to then adjust to what you need to feed something else in the chain.
Old 6 days ago
  #12
Gear Nut
 

Quote:
Originally Posted by Pro Sound Guy View Post
Run the input gains and output normal on the UI24R for good gain structure.

Use the main physical R/L outputs on the front of the Ui24R to then adjust to what you need to feed something else in the chain.

LOL, I just looked at the front and noticed it had mix L/R output level attenuation. that makes things a lot easier.

If the pots for mix L/R level are just attenuators then it should be really good.
Old 6 days ago
  #13
Lives for gear
Quote:
Originally Posted by Swfullback22 View Post
Also, what is the risk of damaging the FOH mixer if we did accidentally turn up the main out from the UI24R? Would it damage their board or burn the channel out?
Not likely. So long as you don't connect 240v mains to the channel strip, you'll be absolutely fine.

I'd set your main output at 0dB, and tell the house tech you're sending a line-level signal, they'll set their input trims accordingly to avoid distortion.

This isn't rocket surgery, and I think you're over-thinking it.

Chris
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