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Live audio amp levels

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Mark Frazier
Live audio amp levels
on Dec 13, 2011 at 8:48:42 pm

I need some advice/opinions from more seasoned audio professionals. Since my background is in video production, but run live sound frequently, I'm getting conflicting opinions on output settings of the amps.

When setting up a mixer and amps for live audio, I've been told (mainly by the installers) that the amps should be set first - usually at 80%-100%, depending on the installer - and then adjust the board output for proper volume. This has always created levels that do not read, or barely read at all, on the output meters of the board.

This causes two issues for me: Since I'm not actually in the room where the band and speakers are (I can only hear through a window between the rooms), I can't get an accurate "level" when things are happening. No usable meters on the board = take your best guess.

Also, when monitoring with my headphones, switching from the main mix output (which has to be pulled down to keep from blowing the audience out the door) to checking a channel in Pre-Fade Listen blasts my eardrums, since the raw input level of the mics & instruments are so much higher than the mix (this board does not have a separate volume control for the PFL level.)

My approach has always been to set and balance the board inputs and outputs so the meters actually mean something, then adjust the amps for proper room volume, which usually ends up at 40%-60% amp output. Is one of these better - or more "proper" - than the other?

Thanks for any and all responses.

Mark


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Eric Toline
Re: Live audio amp levels
on Dec 13, 2011 at 10:10:38 pm

Your approach of setting the board for meaningful levels and then raising the amp level for room volume is how I have done it. Same as setting up your mixer and adjusting the headphone level for your comfort.

Eric


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Jordan Wolf
Re: Live audio amp levels
on Dec 13, 2011 at 10:33:04 pm

Mark,

I do not wish to step on any toes, but there is another forum that I feel is better-suited for this topic. You'll want to register and use your real name as your alias. PSW has been invaluable to me as a SR engineer.

Wolf
<><


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Ty Ford
Re: Live audio amp levels
on Dec 13, 2011 at 10:58:09 pm

Wolfie,

This ain't brain surgery. Unless he's running major systems where every watt counts while doing live sound, his way works just fine. And in that configuration, the amount of power and the power handling capability of the speakers all has to be micromanaged so you don't blow up the speakers. That you do have to be aware of.

Mark, you didn't give me the impression that big PA was what you were doing.

Regards,

Ty Ford

Cow Audio Forum Leader
Want better production audio?: Ty Ford's Audio Bootcamp Field Guide


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Ty Ford
Re: Live audio amp levels
on Dec 13, 2011 at 10:53:16 pm

Hello Mark and welcome to the Cow Audio Forum.

Go with your instincts. Get a good level coming out of the console/mixer given its metering and adjust gain on the monitors as needed, then leave the monitors alone.

My Hafler P4000 Power Amp is set to between three and four (out of ten) .

Regards,

Ty Ford

Cow Audio Forum Leader
Want better production audio?: Ty Ford's Audio Bootcamp Field Guide


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Mark Frazier
Re: Live audio amp levels
on Dec 13, 2011 at 11:34:45 pm

Gentlemen, thanks for confirming what I felt was right all along. For some reason, I've had people consider me "unusual" because I like to read meters, listen with headphones, etc. Must be some anal-retentive quality-control hangup of mine.....

Thanks again!
Mark


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Richard Crowley
Re: Live audio amp levels
on Dec 14, 2011 at 7:04:57 am

That "preset" recommendation is severely misguided. Your preference for staging levels for optimum performance at each link in the chain is the proper way to handle it.

You don't want ANY stage to be operating "down in the mud" at less than optimal signal-to-noise ratio. OR clipping against the top at the other end and severely distorting, either. The metering system on a mixer is there to help set optimum channel gains, mix levels, subs, and master output levels, etc.

How much front-panel gain any particular power amp needs to produce the desired SPL in a room is NEVER a "preset" kind of adjustment. Ever. I recommend taking no further advice from that clueless source.


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Peter Groom
Re: Live audio amp levels
on Dec 14, 2011 at 10:29:23 am

If youre just doing pa mix then i dont suppose it matters, bur then when a tv crew walk in ans ask for a desk feed, it will be so low as to be useless, and there not much can be done about it without destroying the pa level setup.
Id suggest having each input on the desk at sensibly readable levels on the desk meters, then turning up the amps to the right level for your ears.
Peter

Post Production Dubbing Mixer


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Mark Frazier
Re: Live audio amp levels
on Dec 14, 2011 at 4:11:00 pm

Peter, usually these setups are just PA mixes, and if that's the case it may not matter much (to other people.) But I have been that TV crew that needed a feed - or just trying to record the mix for later playback - and it ended up being almost useless. I guess that's why I think the way I do.

Now if we could only get these salesmen/installers to understand this. Maybe a subtle link to this forum.......


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Eric Toline
Re: Live audio amp levels
on Dec 14, 2011 at 5:01:13 pm

If you get a feed from an aux buss out, the level can be controlled independent of the main mix out.

Eric


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Peter Groom
Re: Live audio amp levels
on Dec 15, 2011 at 10:40:33 am

Agreed Eric, if theres a spare aux. Dont show up at one of my gigs 10 mins before curtain expecting a spare aux tho. My desk always runs out of busses before my need does. No spares for a tv crew who show up minutes before.
Peter

Post Production Dubbing Mixer


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Bouke Vahl
Re: Live audio amp levels
on Dec 15, 2011 at 2:42:25 pm

well, i often do broadcasts of live events, and most of the time i get a feed from the PA.

I always bring my own mixer just to amplify that signal, as it is always way too low, even when i get a feed from a seperate bus dedicated for me.

No idea why, but indeed it seems SOP to set the amps up high and use the main out of the mixer for volume control. I don't get it at all, since that involves the risk of someone making a mistake and get the entire audience deaf, let alone i believe equipment performs best when levels are at a reasonable high level, way before the equipments overloads / clips.

Bouke

http://www.videotoolshed.com/
smart tools for video pros


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Kingsley Foreman
Re: Live audio amp levels
on Dec 16, 2011 at 8:50:23 am

We always ran amps at 100%, and made sure the sound wasn't peaking at ether the crossover (Active System) or put a compressor in front of everything if we didn't trust the mixer.

And just checked the amps for peaking while the gig was going


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