Why does key-change from C to C♯ sound so exotic than C to D♭?

Question

I downloaded and retuned Night Walk from Rhythm Tengoku from 12edo to 19edo, along with some tweaks (correction of key signatures, and correction of range of the glockenspiel)

The original piece goes from C Major to D♭ Major, then to D Major, and then to E♭ Major.

When I retuned those to 19edo, it didn't sound too different. The chords sounded like slightly different quality, but not too much.

Since C♯ and D♭ are different notes in 19edo, I tried interpolating between C Major part and D♭ Major part with C♯ Major. And that's where it sounded so exotic. I won't say it's horrible though.

What's the reason? You can listen to the modified version here. (WARNING: tuning doesn't work in mobile version of Musescore.)

Answer 1

I will venture a mix of reasons, which I won't claim to be scientifically justified but I think substantially account for this experience. The two-step 19edo semitone (~126cents) is closer to the familiar 12edo semitone (100cents) than the one-step 19edo semitone(~63cents), although both are quite far off. However the two-step semitone is considerably closer to the "just diatonic semitone"(16:15=~112cents), which there may be justification for thinking this is the 'appropriate' semitone when we are doing a parallel key shift, though your mileage may vary. There also exists the "chromatic just semitone"(25:24=~71cents) which is in fact closer to the one-step 19edo semitone. However I think a considerably part of accounting for this experience is simply that a wider shift simply feels more acceptable to our ears than a narrower one. In the narrow shift the tones are too dissonant with the established preceding tonality, to a greater extent than with the wider shift. This is where I don't have a scientific justification, perhaps someone else can fill one in (or refute)