Hello, Sian. You asked what tune we are using. It's this tune:

calon lan with pretty pictures

There's a MIDI of this tune on the Kunst der Fuge site with a lovely arrangement by Barry Taylor.

Thanks to all who have helped with Calon Lan.
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About the pronunciation of Coed. If you say co-ed, then you say it faster and faster, you get 'coid.' So the two different pronuciations are not that different.