This letter (image below, PDF also attached) circulated around our forum a few years ago, and I think over on the NLM too. Where exactly did it come from — that is, what online source, if anyone knows — and where might it be found now? I've scoured the internet, but to no avail. I know it was up on one of the Watershed websites for a while.
Judging only from appearances, it is a set of norms devised by the choirmaster of St Peter's Basilica and applies only to choirs which sing there. It is not "universal" in application (albeit the norms are worth consideration for any parish choir).
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