Gain Structure - Setting the PA System Levels

[Walker]

I’ve been researching and reading about setting gain structure for correctly setting up our new PA system.
The Yammy desk manual only goes so far but I found an article on the Mike Rivers Audio blog (that was originally written by Recording magazine as far as I can gather), that explained it to me.

Thought I would share for those interested: [url="http://mikeriversaudio.wordpress.com/technical-articles/"]http://mikeriversaud...nical-articles/[/url]. It’s the third article down.

If you are just interested in the suggested process, read from “Taking it From The Top – Setting System Levels” and skip the technical stuff.

[b][color=#ff0000]QUICK QUESTIONs:[/color] Also, I’ve read elsewhere that if you have an acoustic guitar/mando/banjo, etc with an on-board preamp, he/she should run it at maximum volume to get the best S/N ratio. Is that correct[/b]?

[b]Also, in the article, he says if you go from the desk into other gear (GEQ, X-Over, etc), you should boost that gear to just below clipping to get the best S/N ration. I've always assumed that running stuff between the desk and the power amps at unity would be best so the signal 'passes through' rather than gets boosted. Am I very wrong?[/b]

Thanks for all the technical help you guys have given so far, it's been a huge help setting up our PA!

Cheers

Chris

[Walker]

Are my usual PA consultants around?!!!

[mdc]

Hi Chris
In general you want a nice strong low-noise signal at the input of any stage which has gain, as everything which is fed in will be amplified by the same amount, including any noise present. Provided the instrument pre-amp itself isn't clipping (get your gtr/mando/banjo player to play as loud as possible in the sound check to make sure) you can always reduce the signal level at the mixer input.
As regards different parts of your PA system, ideally you would set all the input levels so that everything in the signal path from mixer input through to power amp clips at the same point, to achieve maximum clean output with minimum noise. If you had already set the input level of your power amp so that it clipped at the same point as your mixer output, then anything you put in between should have unity gain to maintain your gain structure - however the thing you've inserted (GEQ, whatever) would also need to be set up so that it clipped at the same point. If all the units operate at the same sensitivity standard (i.e. 'pro' or 'consumer') and they all have decent headroom, it should be easy to set everything up together.
It's often neater to put things like external GEQ on a mixer fx send/return rather than in series with the main output as it's more flexible and it's one less thing to go wrong in your main signal chain - if something goes wrong it's easier to bypass an fx loop than start unplugging cables.
Hope this helps a bit
Mike

[LawrenceH]

Signal:noise ratio matters most when taking a very quiet input, like a mic or instrument out - I wouldn't worry about it at all for things at line level, it's more important that you don't clip them and it's usual to run things on inserts at unity gain - I definitely wouldn't go boosting the GEQ output, if it has been designed properly then it will have been designed to use in this manner.
If your desk has main inserts, I'd use them for the main GEQ/compressor etc, they can be very quickly unplugged in an emergency

[grandad]

Hi, thanks for the link, lots of useful info' there. We used a Yamaha EMX5014 to mix the whole band & I found it an excellent piece of kit, so much so, I bought the 5016 & discovered what multi-band compression could do to the vocals in the mix.

I did have to educate the other band members into handing over the control of their volumes to me on the mixer as they tended to tweak during the performance. I asked them to give me their loudest signals when setting up. After several performances I became familiar, more confident with metering & quicker at sound checks.

I also realised that although rated at 500W per channel, that's peak/max on the LED meter. With the master volume giving a 0, mostly green & occasional orange the o/p power would be 125W into 4 Ohm & the headroom of 6dB would double that to 250W & double it again to 500W. The point here is that to fill a medium size venue the actual amount of power going out is quite modest really. The 500W per channel is only headroom & not used but in reserve.

Without patience & co-operation from the other performers it can at times seem a thankless task but I enjoyed it when I got a good live mix for a show. The luxury of an off-stage sound engineer is something most of us do not have.

Some advice I received was that with practice your hearing can become more focussed on what you are listening for. The phrase, "a trained eye would have spotted that straight away", is often quoted. I'm sure that the phrase, "a trained ear would have spotted that immediatley", is equally true. Unfortunately I find EQ - ing particulary difficult with my hearing now being on the way out. Do look after your hearing.

You might like to try [url="http://astralsounds.com"]http://astralsounds.com[/url] for live sound tips.

Anyway, good luck & thanks once again for the link. Regards, C

Edited May 19, 2013 by grandad

[Walker]

Thank you all for your help and advice gents.