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AGC or Compression?

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Mike Roy
AGC or Compression?
on Dec 20, 2009 at 3:49:10 am

In my school's auditorium we shoot most shows with our built-in 3 camera video system. For audio, we have four 1/4" cables feeding outputs from our house sound mixer. Our problem is that the house mix is always focused on what the name implies, the sound for the house. This causes issues with the balance of the inputs when we feed our video system.

In an ideal situation, we would take a direct output from each channel on the house mixer and run a seperate video mix upstairs, but with our budget and staffing limitations, this alternative isn't possible.

As much as I would like to convince myself, the students running this system won't always have audio on their minds, (one person runs 3 robotic cameras as well as the switcher and audio levels) meaning at times the audio will be too low, and other times it will distort. Also the performers on stage don't always have the best mic handling/vocal technique, causing sudden dips and peaks. From my experience these dips and peaks are almost impossible to correct fast enough by just riding the fader on the mixer

I have been looking at the different options out there, and to me at least, compressors look like the best solution. All I'm really looking for is an "auto gain control," but all I have seen in rackmount units are compressors that only lower the loud parts, instead of doing that AND raising the quiet parts. Is this what a "compander" would do?

My biggest concern is maintaining the integrity of the sound. I don't want to over-compress the choir, but that doesn't even matter if we can't hear them, or if the sound is distorted.

With our mics and wiring being so out dated, we tend to end up with a "muddy" or "weak" sound. The school band sounds bland, the drums have no punch, and the dynamics are just all over the place. There is no changing our house sound system with our current budget, so I'm looking at other ways to improve clarity, without breaking the bank.

My thought was to take two of the outputs from the house mixer, and run a stereo feed to our small mackie mixer upstairs. From here I will run the feed to a stereo compressor-enhancer-noise reduction combo unit (if one exists). I need something that will level the mix, reduce room noise, and enhance the clarity of the overall sound.

I should mention that I need this for as cheap as possible, and still produce a pretty natural sound... A lot to ask for a unit that would do so much.

Thanks in advance for any suggestions, I really do appreciate all the time and knowledge people put in their comments.
-Mike Roy

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Ty Ford
Re: AGC or Compression?
on Dec 20, 2009 at 4:03:00 pm

Hello Mike and welcome to the Cow Audio Forum.

When I was in radio, I was in charge of the audio chain to the transmitter and all produced sound. We had $5K Optimod processors to achieve our on-air sound. The major market air staff thought (erroneously) that all that high tech stuff meant they didn't have to watch their levels. I had to disabuse them of that notion. I told them that they were now driving the equivalent of a Maserati and they needed to be very mindful of the levels to keep the station sounding great.

There are several circuits that do a surprising amount of level control, but none to the extreme you wish to achieve. The Aphex Compellor is one.

You would not be the first person, by any means, to hope that there are plug and play solutions for good audio. Good audio comes from good choices in gear, good wiring, good operational practices, and the ability to make sense out of what you're hearing so that you can correct problems on the fly.

My "best bet" advice is to use the educational platform you have to instruct the students of the importance of proper levels and fix the problems where they begin instead of trying to rely on circuits to correct their inabilities.

About your drum sound. So many things can suck the life out of drums that space and time do not permit me to address the problem.


Ty Ford

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

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Mark Barroso
Re: AGC or Compression?
on Dec 21, 2009 at 10:09:32 pm

I second that. Sometimes there's no way around hiring a professional, or teaching a volunteer who wants to be one. This is a classic case. Is it the curse of auto-focus, auto-iris, point and shoot modern mentality that everything will be great if I buy the right gear or software? There's a reason why a lot of audio sounds amateurish - it's because it's recorded by amateurs! And the solution doesn't exist on the internet.

It's not a snob thing, it's knowledge and experience. If there was something out there that did what you wanted, Mike, there would be no bad sound and no sound guys, for that matter. The money you want to spend in post will be twice what you pay for a sound person and the quality half as good.

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Mike Roy
Re: AGC or Compression?
on Dec 22, 2009 at 12:11:12 am

I think my original post was a bit misleading as to what my goals are. I agree with you both 100% when you say there is no substitute for a well trained operator. It has never been my intention to create an "automatic" system that will always be perfect. All I'm looking for is something to assist the operator in ensuring proper levels, as well as clean up the signal a bit. I'm not looking for the magic processor to solve all for our problems, I just need that extra assurance that we are doing everything possible to send a consistent audio signal to our recorders.

As for the compeller, I read the specs and it sounds like it could be a pretty good match for our system. Does that unit work well for live audio (for video) recording, or is it more focused on radio and broadcast use?

I appreciate the suggestions, I promise I'm not "that guy" who is always looking for an easy and automatic solution. We are doing everything we can to clean up our wiring, balance our levels between different mixers, and most of all teach the proper way to run the mix during the show.

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Jordan Wolf
Re: AGC or Compression?
on Dec 22, 2009 at 6:52:50 am

"All I'm looking for is something to assist the operator in ensuring proper levels, as well as clean up the signal a bit."

Well, you need to make sure the levels you are getting are within the tolerances of your gear's inputs. Are there any free post-fader Aux Sends on the FOH console? If so, I would use one (two, if possible) and get levels set during sound check. I would insert a compressor (like the Compeller or a TC Electronic C400XL) into the Aux Send(s) and set a ratio of 4:1 with a fast attack and fairly fast release time. If there's a "knee" control, set in in the middle (not hard, not soft). Set the threshold so that there's around 6dB-8dB of compression at the most. I highly recommend a multiband compressor of sorts, as that can really clamp down while not destroying the mix.

Just my thoughts.


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