Jack Campin:
"- the tempo of the music
- the number of musical events per second

And they don't correlate. Typically in classical music, slow movements have more notes per second than fast ones. And a good unaccompanied singer or solo instrumentalist doing a metrically very slow piece will add so much ornamentation and so many rapid variations of timbre and dynamic that the rate of musical activity can be far faster than a reel."

A very helpful clafification that Jack.
I've just memorised Lowlands, and sing it quite slow - as I feel is fitting..
Then reading on this thread (and elsewhere on Cat previously) about complaints concerning unaccompanied singers dirging away at songs, made me think "Oops!!"
I don't ornament constantly (or at a highly intricate level, as I'm not vocally athletic enough), but having just tested the song without ornamentation, I find it sounds pretty dull by comparison.
Another minor peice of illumination, that will be stored away for future reference.