[noncovalence]

In the context of the difference between D# and Eb, 19-TET is very interesting to play around with. It adds an extra black key between every pair of white keys, and most songs intended for 12-TET still work fine, as long as you play sharps and flats as written. If you play a D# instead of an Eb, you suddenly get a very different sounding interval.

[bonzini]

Also as long as sharps and flats are written in a very pedantic manner. For example a diminished C chord only sounds "right" if it's notated as C-E♭-G♭-B♭♭ rather than C-E♭-G♭-A.

On top of this, harmony may or may not work the same in 19-TET and 12-TET. With the same example of diminished chords, the diminished chord does not divide the octave in four equal parts in 19-TET. Adim and Cdim are enharmonic in 12-TET, but Adim in 19-TET is A-C-E♭-G♭♭; that is, only C and E♭ are the same.

[sobjornstad]

Wait, how do you play B♭♭ differently than A on the 19-TET keyboard? There isn't a separate key for that is there?

[bonzini]

In 19-TET, B♭♭ is an A#, which is two "steps" below B.

BTW I was wrong in that Adim is A-C-E♭-G♭. Still not enharmonic to Cdim, and probably diminished chords sound weird in general because G♭-A is four 19-TET steps, which is a 19-TET step smaller than a minor third. It probably sounds halfway between a semidiminished chord and a regular diminished chord.