Thanks for answering!
I see your point and will follow your 2 mik set advice.
In fact I´ve been doing about that way before but I´m seeking a way to broaden the stereo picture.
I´ve tried to do that in Vegas but haven´t succeded.
I would be glad to have some hints on broadening stereo in Vegas.
/Aje

I have done perhaps a dozen surround-sound documentaries over the past 8 years. Most of them have been of the Oregon Children's Choir & Youth Chorale as they performed in France, Austria, Italy and the Czech Republic on their summer tours.

Audio capture was usually with two Sony MS-908C stereo microphones, which are surprisingly decent mics once the response curve is flattened. Both mics were mounted on the camera (a Sony FX1) with the forward one recording to tape and the second mic facing aft and up at a 20 degree angle. The output of this second mic was captured to Minidisc.

Other than reminding myself to make sure the Minidisc recorder was rolling whenever I shot video, the setup was trouble-free. Since the Minidisc was not synchronous with the camera, I got into the habit of unobtrusively hitting the mic mount with my wedding ring on my finger at the end of every take, putting a sync click on both sets of audio, though these days I could probably get away with using something like DualEyes.

After the video aspect of the project was finished I would turn to the audio. 5.1 is unnecessary and a bit silly as a center channel is not needed for non-theatrical delivery (the center channel was created by Dolby to insure that dialog came from the center of the movie theater screen, no matter where you sat in the theater). The ".1" aspect was meant to be for special sub-sonic effects such as explosions and T-Rex foot stomps. So I built my audio around DolbyDigital 2/2--two front channels and two surrounds.

Once the rear audio was synced and cut to match the front audio segments, I put it on the timeline and mapped it out to the rear speakers, remembering to swap left and right rear channels (because the mic was facing rearward). Then one carefully balances the rear levels to match the front for ambient sound.

You know the effect one gets in going from a single channel to stereo? You get a very similar effect going from stereo to 2/2. Seriously. When the choir sings in Chartres cathedral, you hear them but you also hear the remarkable acoustics of that place. Walking with the choir Steadicam-style across the Old Town Square in Prague, you hear people in front of you--and behind you. It's a bit unnerving at first, but shortly becomes very natural. If you then cut out the rear channels on purpose, you realize how artificial 2-channel stereo really is.

Anyway, that's the way I see it. Surround-sound is a PITA and adds significantly more complexity to already-complex video projects, but the results are very cool if done right.

I'd suggest that surround-sound also is quite effective even in a hall without the reverberation of a Chartres Cathedral. A surprising amount of audio comes back to the camera from the rear of the hall, and the timbre of the sound and the time delay subtly tell the listener a lot about the environment. Plus the occasional cough from someone behind you and, of course, the applause at the end. But experiment for yourself and see if it's worth the added effort.

You also asked about how to set up Vegas to actually do the edit. It's very simple. As you already know, you tell Vegas you are doing a 5.1 project, and Vegas will put a panner-style box in the audio panel. You can map the surround audio by just putting the audio on that track and moving the little red diamond to the bottom, midway between the little speaker icons. Needless to say, you need to be editing on a PC equipped with a surround-sound card and speakers. The front audio gets moved to the top of the box, in similar fashion.

Oh, and on my particular version of Vegas and drivers, I found that I was not able to access those rear audio channels unless I chose "Direct Sound" on the Options/Preferences/AudioDevice page.

When you are ready to author to DVD, your setup is probably different from mine. I use an external authoring program (DVDlabPro), and that program insists on elementary streams of m2v video and ac3 audio. It is in the encoding of the ac3 audio that you tell Vegas to build a DolbyDigital 2/2 ac3 file. I use a bitrate of 384Kb/s.

" I use an external authoring program (DVDlabPro), and that program insists on elementary streams of m2v video and ac3 audio."

DVDA likes separate streams too.

So far as whether to use stereo or quadraphonic for a choir, I guess it depends on your likes and dislikes. Personally I would like to feel that I was the only one in the audience, and be able to hide audience noise as much as possible.

I fully agree that surround sound is appropriate for a walk in a historic square with hustle and bustle all around matching the activity you see in the video. But I hate the sound of cars going by behind me when they are not in the picture.