Another question for my amateur Shostakovich Symphony 11 arrangement for solo piano. The part I am asking about is 29:36 to 29:56 in this video, or rehearsal marks 80 to 82 in the original score. I'm ignoring the strings/woodwinds since pianists only have two hands, and I'll have the right hand play the higher brass chords while the left performs the trombone/tuba glissandi. Here's the extract in the original:
The low brass glissandi are a fun effect; it is continuous over a half-tone interval so microtonal if you want to play it exactly as written (doable for trombones, not so much the tubas, very much impossible for pianos). I've made chromatic grace note effects out of it:
Now I am pretty satisfied but there's one effect heard in the recording, and in my mental version, that I'm not sure how to convey; the horn/trumpet chords are slightly disaligned with the trombone/tuba glissandi. Ignoring the glissandi parts and listening carefully to the beats on the natural notes E, F, F#, G, G#, A, Bb; in my experience they are at first slightly behind the horn/trumpet chords, and when the melody modulates they get slightly ahead of those chords. It's played asynchronously, arguably "messily", and I think that's both fitting in this section of the score and sounding very well.
Listening to different recordings you can see several approaches to this passage: synced - slightly out of sync - out of sync - very out of sync. So asynchronity is not totally unique to one recording. In any case, I think my arrangement should suggest it as an option, which I would put between parentheses to clarify that it is my instruction, not Shostakovich's.
How do I tell or suggest to the pianist to mimic that effect, to play it messily, asynchronously, like they are playing in the midst of the Russian Revolution (or the communist regime, depending on whom you ask), and everything is death and awful and the metronome doesn't matter because terror is everywhere.
Somehow I feel rubato doesn't cut it - it also doesn't usually mean asynchronity between the hands. Is there a fitting Italian term available, or should I just put all that context in an English footnote?