But at a folk-club, Marje, when folks who know the tune and words all join in, they are (usually - I once got some sophisticated accompaniment to The Drunken Sailar, eg.) singing the tune/top-line-melody (if chords/base notes have been added to the score) in their natural voice, and it can, of course, sound great, John - but it wouldn't if they were singing in a different key, with it's different top-line notes..?..so if I intoduced a chorus on my recorder, then transposed it to another key, we would then ALL have sung it in two different keys..?..or if a natural-tenor and -base (which is not an octave apart) both go doe-ray-me...they are NOT singing in different keys..?!..they are both singing in C, yes?!!
I was thinking of fair-competition with these BBC Young Musician Awards (you accept that pianists, themselves, can be off-form) but, of course, classical music is very much about harmonies...perhaps they should all use a pre-recorded accompaniment, CR..?