coompressors and hum eliminators

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mutt

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I'm trying to get some info on two things:

For our live performance rig, which is:
12 channel DOD board, routed through a Rocktron effects unit, signal sent to the
Soundtech monitor amp on monitor outs, and signal sent to DOD eq unit before going to Crown power amp. We mic 4 vocals, 3 instruments, and the Yamaha electronic drum set.

1. Compressors - what would be the right type of compressor. Would one compressor unit control everything that is miked? How is it set up in the sound chain? (between the board and eq unit?) Can you assign the signal to route to the compressor via an effects send, so that each channel can control the amount
of compression? (As you can tell, I know NOTHING about compressors)

2. Hum eliminator- Is there a hum eliminator on the market that can connect to the main power source for our entire rack (board, main and monitor amps, effects, and eq unit) or do you have to have a separate one for each piece of equipment? Or, do you generally connect the hum eliminator to only the board?
Again, do you recommend any particular hum elim. that would be right for our rig?

After our last gig of having "a certain person's voice" setting off the feedback and
overpowering the mix regularly, I think we need to look into a compressor, or something!!@!@!
(I posted this on a couple of groups because I'm not sure which one it fit the best)
mutt
 
The hum problem needs to be isolated to see where it is coming from. Any one of your devices could be generating it, or it could be bad cables, or it could be the proximity of one device to another and picking up its electromagnetic field and amplifying it. Try bypassing and/or unplugging each component in turn and find out what stops the hum and then deal with that problem unit or source. Also try physically separating components and see if that helps.

As for a compressor, my question would be, what problem are you trying to resolve with compression? You need to diagnose the disease before you prescribe a medicine, rather than selecting a medicine and then figuring out what you might use it for.

Compressors (depending on how they're designed) mainly help even out a signal--think of your sound as a sponge--the compressor is a vice that squeezes it so that the loudest and the quietest sounds are closer together. If you compress something a lot, whether you speak quietly or shout, it will come out the other end at the same level. If you have a singer who goes from a mumble to an ear-splitting wail, setting off red lights all over your board or seriously bending your VU needles, you need to compress the signal (or feed the singer a box of dry crackers). You can use the compressor either on individual channels or the whole mix (usually on the whole mix--the idea is to prevent an inexperienced operator from blowing up the system by accidentally sending it a killer blast--here's the usual scenario--a channel doesn't work, so they turn up the fader to the top--still nothing so they turn up the input gain all the way--still nothing, then they go--"Hey the mute button is down" jabit and watch in numb horror as bits of paper cone eject from the house speakers and smoke puffs out of the power amps--a compressor set hard to squash the sound at a certain level performs this type of "limiting" function on the mix).

Compression is not usually the first line of defense on feedback. Usually mic placement (in relation to both house speakers and monitors), eq settings on the input channels and the outputs will make a difference. If feedback is your main problem, I would sooner use a graphic eq on the monitors than the house (if you can't afford one for each). Yes, your house mix won't sound as good without it, but most feedback is caused by the monitors and you can at least eq out the problem frequencies. No house mix will sound good if feedback problems exist--you gotta fix those first.

Compressors are not fed by aux sends as these only tap off the main signal and therefore won't affect it. You can't mix a compressed signal back in to your main mix along with the uncompressed signal and expect anything useful from that (heck you never know--somebody will come up with some example of where it did something cool for them--but I can't think of any right now--never say never in this business). That's why most boards have "inserts" which allow you to insert the compresser into the full signal stream.

By the way, did I understand correctly that you're running your whole mix through the effects processor? If so, that's not a good idea. Rather, feed it from the aux sends--that way you control how much of each channel gets effected. That in itself could cure your feedback problem. You won't get as much noise from your unit either.

Hope this helps.
 
Thanks, tapehead, for the info.

I should have been more clear about the effects: we send them out via the effects send, which we do control channel by channel.

Regarding the compressor, you said that most boards have an "insert"?? I don't think our board does?? Could it be called something else, like a type of output or send?
If not, what else could we do. (One of our main problems is the singer who goes from very soft to very loud)
 
An insert is simply another 1/4" input (*but see below). It should be at the back of each channel right around where the XLR and line inputs are. If there is only one 1/4 input for each channel, then that's your line input and you don't have inserts.

Some boards have inserts only for the main outputs so check there as well.

*The insert socket is a TRS type input (i.e. tip-ring-sleeve) which requires the use of a three-part 1/4" plug. The cord you'd use actually would look like a stereo 1/4 cord--i.e. just like the plug on your stereo headphones. This allows the signal both to be sent to your compressor (or eq) and returned in its processed format to the same channel with only one plug. (Depending on the compressor, you might need to split the signal using a splitter jack from one "stereo" to two "mono" plugs to match the input/outputs on your compressor.

If you don't have a channel insert you could (I haven't tried this but don't know why it wouldn't work) use a channel aux send to feed to the compressor, then return the compressed signal to another channel where you can eq, assign, effect it, etc.

I think you may have been suggesting this earlier but I didn't think this possibility through, for which I apologize! Let me know if it works...
 
Hi Tapehead
Thanks for getting back to me so soon! I checked our board (it's a DOD 1222) There is no "insert" jack or auxilary send, but it does have a monitor send (which we are using, obviously), and an effects #1 send and an effects #2 send with two separate effects knobs for each channel (we are using the effects #1 send to our reverb unit and routing it back into channel 12 so we can control the amount of reverb to the monitors and mains separately) We don't use the effects #2 send. Are you saying we could use that for the compressor? And would we route it back through the effects #2 return, or to another channel like we did with the reverb? (The effects returns have two jacks each (stereo -left/right) although they have only one output jack for each effects send.)
Thanks again for your help!!

mutt
 
Both monitor sends and effect sends are the same as auxilliary sends, only under a different name. Only thing is monitor sends are usually pre-fader (i.e. once you set them both at your channel and at your master section, they operate independently of the channel fader). The purpose for this is as you mix and adjust the levels, you don't want the monitors to be affected or you'll get some very dirty looks from your musicians.

Effect sends on the other hand will be post-fader. In other words the signal you send to your effects unit will follow your channel fader adustments That way it maintains the effect in proportion to the main channel fader position. Otherwise even if you faded a channel all the way down, any noises picked up by that mic or other device would still be sent to the effects unit and broadcast. Horror show.

So your situation is not ideal but still possibly workable. Let's call your original channel 1 and your "effect (compressed) return channel 2. Your main monitor send is obviously committed so you can't use that. So you have to use an effect send. You'd therefore be using a post-fader. Also you're not getting the advantage of compressing the signal before the input stage so you'd probably have to down the input gain or trim somewhat to avoid clipping (if you have an insert it actually introduces compression before the input amplifier to avoid precisely this problem).

Back to using an effect send, it's not orthodox but you could try it. You're probably better off returning it to a channel as you can eq it, assign it and effect it as necessary. You can even use that monitor send to feed a compressed signal to the monitors. You'd have to keep the original input channel fader up as, remember, the effect send will be post fader. If the fader is down there won't be a signal even if the Effect 2 send it turned all the way up.

So how do you avoid sending that channel to the mix--simple--un-assign it (make sure it's not assigned to the LR (main) mix or any of the sub-mix faders (if your board has any).

Anyway, as I said before, I've never tried it, and it may sound hokey, but if it works, what the heck! Good luck.
 
Thanks again,
I was following you really good until you mentioned "avoiding sending that channel to the mix - unassign it"
If I route the signal from the effects send to the compressor and back into an empty channel (say channel #11), from there it goes out via the main outputs, right? So what do you mean by unassign it? (the board is only a stereo out, so there are no subs) Do you mean to leave the panning knob centered instead of left or right?
 
Sorry, I should have been clearer. In this configuration you're actually using two channels. Channel 1 in my example is a "dummy" channel--all you're doing is using it to plug in your singer's mic so you can use Effect 2 on that channel to send a line signal to the compressor. You then return the compressed signal to Channel 2 (11 as you have it set up), where you can then use the Monitor send to feed a compressed signal to the monitors, Effect 1 to effect the signal, and the Channel 2 fader to send it to the main output.

What I'm saying here is that you only want to send the compressed signal from Channel 2 to your main output. You don't want to send any of the uncompressed signal that's also coming in to Channel 1 to go to the main output. So if you have an assign switch on your channels that can assign/unassign the signal from Channel 1 to your main outputs, use that to cut Channel 1.

(I wish I knew more about your board.) Anyway if your board doesn't have assigns, and if you have a pan pot on each channel, then obviously you have two main output faders (Left and Right). But since you're obviously running mono, have all your operating channels panned right and they will only assign to the Right output fader. Make sure you are feeding your amps from that main output (the right one) only. This is perfectly fine.

Then pan Channel 1, which we don't want into the mix, Left. That assigns the signal to the left main fader which you're not using. So now you won't hear that channel even thought the Channel 1 fader is up ('member, it needs to be up otherwise you won't get anything coming out of your Effect 2 send on that channel). Hope this helps!

[This message has been edited by Tapehead (edited 03-14-2000).]
 
Another thing you can do of course is get a simple mic preamp, plug the singer into that and run a line from that into the compressor and from the compressor to a channel. But hey if we could buy every answer we wouldn't have to get creative!
 
Well, I was "sort of" on the right track, except for the right only out. So, instead of having two lines (a left and right) from the main outputs on the back of the board which goes first to the left and right side of our eq unit, and from there to the left and right input of the power amp, we would only have the right output feed one side of the eq unit, then one line from the eq to the amp? Then bridge the amp to mono? (We have a Crown CE2000 amp which I know can be bridged mono, but have never read how to actually do it.)
I considered the preamp thing, but can you find a preamp with four to six mic inputs that doesn't cost a fortune? plus we only have room in our rack for one more one space unit, so a separate preamp and a compressor wouldn't work unless they were both 1/2 rack space.
Thanks again for your help.

mutt
 
Yes to everything in your first paragraph. However, Crown amplifiers can be run in bridged or parallel mono modes, depending on the speaker impedances and configurations. There are instructions on how to do both on their website at:
http://www.crownaudio.com/crownaudio/amp_htm/ampfaq.htm

I don't want to be responsible for blowing up your system so I'd recommend you contact Crown on that--I'm sure you could email them.

As a side benefit you now have freed up a side on your graphic eq which you could use on your monitor signal to fight your feedback problem.
 
On second thought, you're already running the Crown in bridged parallel and it's working for you so why not just leave it that way. Just use a splitter from the single eq output to supply both sides. The Crown should have no problem handling the lower input impedance.
 
I see what you're saying - however, I just had a another thought that puzzles me.

If I pan all of the miked channels to the left, feed them all through the effects 2 send, back into a single channel, then do I still have volume and eq controls for each individual channel? Or does the input channel fader (say - channel 11) then become like a main fader? Am I still able to control the individual channels that way?
 
The effect sends are post fader so they are still controlled by the individual channel faders. Some channel eq's affect the Effect Sends, others don't. You'd have to test it out with your ears.

However, I thought you were only talking about one problem channel (i.e. a singer). If there's several, then you are probably better off running your main mix through the compressor. Whoa that was easy, huh...
 
Thanks again for all of your help.
I think I have enough info to give it a try.

mutt
 
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