Advice on recording a concert
 

I am shooting a small concert in a church hall and want some advice on how best to capture the sound.
I own a Canon XL2, which (as I understand) can provide me with two channels of 16 bit sound through the two XLR external mic mounts (somebody correct me if I am wrong).
My plan is to take the first sound feed from an ambient mic, which I am going to try have suspended above the center stage area. The second sound feed will come from the mixing board (after the mixing has been performed).
Unless somebody comes up with a better plan, this is what I will be doing.
I also plan on setting sound level adjustment to auto adjust because I really want to focus on my shooting and not get distracted. I have shot lots of news footage in the past, but never a concert, so I really don't know what I am doing. I just know that I want to get a good quality sound for a promotional DVD that I will be making. I will be doing my post production in Premiere Pro 1.5.
Also, any suggestions on good affordalbe mics would be a great help.
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Having the audio levels set to "auto" rarely if ever wiill give you a decent sound track, doubly true with music. Can you get someone to assist you with working sound as you shoot?

Or if you have no choice but to work alone, can you attend a dress rehearsal and determine the proper levels ahead of time?
Also as I understand it, the XL2's XLR connectors can't accept a line-level signal. So you need to attenuate the feed coming from the board. How far away is the sound board? Will you be running any of your equipment on AC power?

Steve and Jay,

As far as using the auto levels, I gues I can do it manually. The XL2 provides a sound bar for each channel, and the adjustment is pretty easy to do on the spot. I just didn't want to worry about it if I didn't have to.

As for live level signal capabilities and having to attentuate, I really don't know what you mean. Could you elaborate.

The soundboard shouldn't be more than 50 feet away, and I have a four hour battery, but I was considering using AC power. Why does it matter?

Thank you all very much for your help.

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Using auto mode for audio can give good results. In my experience, musical content is actually easier to do a decent job with than dialog, because noise is less of a factor, and the listener has less fixed expectations of what sounds "right." The main penalty is a reduction in dynamic range (difference between loud and soft). This matters more for classical music than for other types. But even then, I'm inclined to agree with you that messing up other aspects of the production because you're fussing with sound levels is a worse penalty. As you get more experienced you can do more things at once. Like with riding a bicycle, at first it's all you can do just to not fall down.

Jay spoke of attenuating line level (not "live level") audio from the board because the standard line level signal at which mixers and amplifiers "talk" to each other is at a much higher voltage than mic level, so the inputs to the camera will overload and distort the sound. An in-line attenuator reduces the voltage level. Look up "AT8202" in B&H's encyclopedic catalog at bhphotovideo.com for an example. You'll need 30-40 dB of attenuation. I normally use two AT8202's when I take a line into my cam, one at the board set at -10dB, and the other at the camera where I can switch it between -10, -20 and -30.

There's also "pumping" to contend with when using ALC and I find it very distracting. During quiet passages the gain is increased which means not only is the music louder than it should be, noise is also increased. During silence it goes all the way up trying to catch something that isn't there and the noise becomes very apparent. When a sudden attack occurs in the music it often follows silence or a soft passage which means that the gain is wide open when it occurs. It takes time to clamp it down so we have the risk of overload on the first note(s) and then a decrease in volume that's not actually a part of the performence as the level control kicks in and backs off the level. IMHO, about the only thing worse than using ALC is not to be able to get any sound at all. It's better then nothing.

Steve, theoretically that's true, and it probably happens to a noticeable degree in some cams, but it just hasn't been a problem with my GL2, Pany GS200, or Sony TRV22's. I think that the problem is not unknown to design engineers who sometimes sit around a table and discuss what they should aim for in a product. I think today's AGC is better than it was five years ago. I do run my main cam in manual mode and that's where I record my main audio tracks. But I've used the others in two and three camera shoots and listened to the tracks they recorded in auto.

I admit to not having any direct experience with those cameras so it may now be substantially better than my recollections.

And I do agree that if you have the choice, manual is better.

And now for something completely different...
Well, not totally different because it was mentioned and is an important point for any recording in a fixed location when taking a feed from the house sound system.
If two pieces of gear are running on 3-prong AC power and are separated by a physical distance, then it's likely that they'll be plugged into two different AC circuits that can have a difference in their ground potential. This difference can show up as noise in your recording, and it's noise that using balanced circuits with good XLR cables can't defeat like some other sources of unwanted noise that can be simply blocked out.
To eliminate a ground loop hum, you have several safe options. You can run all your gear, including any video monitors, on battery power. You can use only AC equipment that's designed to be run on 2-prong polarized AC power. You can run a heavy AC power cable from the same AC outlet as the soundboard is using. You can use an isolation transformer like an Ebtech Hum Eliminator. Or you can use a passive direct box with a ground lift switch. This box can also have attenuation built-in, so you kill two birds with one stone in this case.
You shouldn't defeat the safety ground on your AC connection when using equipment that requires a grounded connection, it's an unnecessary safety risk.