I just returned from an extended trip where I got to hear a very good performance of the entire multi-movement Christmas work that was the source of my contributions to the 2012 and 2013 Christmas Albums. My most recent post to the listening room also came from this work. This experience really energized me to finish and master a GPO version of the orchestra so that choirs who want to perform the piece can do so without a live orchestra. This is my first time to do this kind of project and I would appreciate all the advice I can get.
Cass and Randy mentioned keeping the recorded ambiance low because the performance hall will add its own ambiance. I think no more ambiance, or possibly a little less, than a stage would add would be OK.
There are other considerations that seem important. First, only a 2 channel stereo sound system will be practical and the choir will need to be able to hear the orchestra. If two speakers are used they will likely be set even or a little behind the choir and possibly angled towards the center. If this is done some extra stage ambiance will be added and the stereo image will be affected. I'm considering panning the harp to the middle of the orchestra because in two movements it contains important parts that will guide the choir through some tempo changes and releases. Both sides of the choir need to be able to hear these harp cues.
I'm also concerned about the dynamic range of the recording. The choir in the performance I heard was almost 150 voices strong and was very well prepared for the concert. Their ff sections were very powerful and their pp sections surprising delicate for the choir size. I doubt that an average sized choir could come close to their volume. It seems I could easily end up with a recorded orchestra that is too loud in spots and not strong enough in others.
Finally, I;m considering adding some instruments that are not used in the live orchestra. It is problematic if a live musician only plays twice in a seven movement work and simply sits for the rest of the piece. However, a GPO instrument can count all the rests a composer wants and enter perfectly every time the instrument is needed. So it seems to me I should take advantage of what the software instruments have to offer.
If you have comments about these items and/or know of other concerns I should have, I would greatly appreciate the help.