Very nice, Mike. Are the Biro parts the ones that seem to have
instantaneous attack? What Biro sounds did you use?
The Biro sounds come in about 1:39 as choir #5 and has seven parts, the first of which sounds like this:
http://www.mikedickson.org.uk/private/Spem%20In%20Alium%20%28Birotron%20Section%29.mp3
Which is Birotron with (tuned down) lead soprano. The Biro parts are all digitised samples as I don't have a Birotron to hand (or maybe I left it someplace...checking pockets....nnnnnnnnnnoo.....can't seem to find it on me...) They sound great, though.
Part of the reason why Spem In Alium is not performed more is because you need to round up eight sopranos who are not only competent singers but who can lead the piece. That itself is a major undertaking.
Mike