Thanks. The piano roll helped me to look at things from first principles - to see how, say, progressing chords towards a change of key you can pivot into the 'allowed' semitones of the new key. Learning about music, the jargon is quite dense, epsecially with the naming of chords and intervals. Thinking of a fifth as seven semitones (and a 2/3 frequency ratio) and so on made it more digestible for me. But perhaps it is a dead end, I might have to take your word for that. Maybe its something like how in chemistry, learning the Bohr modelof electron shells helps you grasp the structure of the periodic table, but then to really get further you have to forget all that and start again with the valence electron model.