It's Christmas again, and that means the "Messiah: Organist on Crack" soundfile is making the rounds again. Everyone's heard the thing. If you haven't, go knock yourself out.
Accordingly, I end up spending most of my Christmas season talking to people at social gatherings who ask me if I've heard it (I have), whether I think it's the FUNNIEST thing EVER (maybe the first time), whether I know the organist on the recording (ummmm. . . no?), and HOW something like this could POSSIBLY happen. I try to explain that many organs are equipped with transposers which, if activated accidentally, could lead to precisely that phenomenon, but by the time I finish my explanation I'm usually standing in an empty room, talking to the Christmas decorations. So from now on, anyone who asks is getting pointed here.
The interesting thing, though, is that I had always assumed a slightly different explanation. The "Hallelujah" chorus is immediately preceded by the tenor aria "Thou shalt break them", which goes up to a top A. It's quite possible that the organist had deliberately set the transposer down a semitone to accommodate a less experienced singer who didn't have the range to sing the aria, and then forgot to change the transposition for the chorus.
The problem with my explanation, I now realize, is that it would involve the organist playing in the wrong key for about FOUR MINUTES before finally twigging to the fact that he had forgotten to transpose the organ. Isn't that the sort of thing you'd mark in your score?