I wrote a canon, to the changes of ‘All The Things You Are’ – I thought it might be a fun challenge, because its chord progression shifts to so many different tonal centres.
This is a strict imitative canon, at one bar’s remove, which means whatever I write for one bar has to fit over the chord of the next bar as well. This is not too hard for, say, Am7 – D7 – Gmaj7, but it’s a bit trickier for Dbmaj7 – G7 – Cmaj7.
Oh, and every bar has to harmonise prettily with the bar before it. I could have done much jazzier harmonies, but I set myself the challenge of lots of pretty thirds and sixths.