(see also Matrix Video)
This is originally a capella choir music. Bruckner had learned about just intonation and had heard a demonstration of it on a special keyboard. Some contemplate that those experiences influenced how he wrote Vexilla Regis [Du 2021].
When I set out to render the piece in just intonation, I was therefore surprised (to say the least) when I encountered a diminished second D♯ - E♭ in the alto part (measures 26, 27). Bruckner couldn't have been that ignorant, could he? Or else it must have been a change by an editor in an attempt to simplify the accidentals.
I was no less surprised when I found out that the diminished second sounds very good here (in my humble opinion), with a modest reverb time to avoid the reverb of D♯ beating with the subsequent E♭. You can witness the diminished second at 56 seconds into the piece and again at 2 minutes 16 seconds.
There is (another) reason why this piece may have been written for just intonation. The piece contains many open octaves and open perfect fifths. In 12 tone equal temperament the sudden (near) absence of beating in such chords contrasts with the fast beating of the thirds in the abundant triads. That contrast may be distracting.
Thirdly, the piece can be rendered without a single syntonic comma.
Did Bruckner know all this?
Vexilla Regis is seven verses on exactly the same notes each time around. However beautiful that may sound when sung by a choir, those repeats are going to be quite boring on an organ. I did only two verses, but used very different stops in each verse. The first verse is with principal/diapason stops as found on most organs, the second with a Vox Humana and a stopped flute. This way you may check whether your appreciation of just intonation depends on the sound.
You may notice (de)crescendos as given in the score I used. I rendered them with a dynamic range which is probably beyond the possibilities of a swell box in a real organ.
Does all the above make sense? Please check:
(12 tone equal temperament)