Instead of having a single MP3 file with all chords, have four
different MP3 files, one per chord, so people can compare them in
whatever order they want, and however they want.

Add also a diminished chord.

Add a hi-hat for reference, so it's easier to identify the upbeats,
and add a slowed-down version of both, so it's even easier to tell
which notes fall together with the hi-hat pulse.