Musical Cryptogram

I'll write you some notes - each one is a letter -
To tell you that there's simply nothing that's better
Than playing the organ — but don't play 'til you drop;
It's very important that you know when to stop.

This piece was written specifically for the Hutchings-Votey Organ in Sayles Hall. Please do not try playing it on any other organ, as you may not obtain the correct result.

Link to this puzzle's contents.