Check this out: https://www.youtube.com/watch?v=wqrJmxy4q3A
About his technique: https://en.wikipedia.org/wiki/Micropolyphony
I don't play or sing any music, so sometimes I'm in awe of a piece but I can't figure out how it works.
At first I thought I was hearing something that required instruments with access to arbitrary pitches within their range, such as voice, violin, or trombone, but then I saw the flutes and that guess had to be rejected.
This 'Requiem' is amazing.
Edit to add: a technical problem on my end had me finally hearing the audio at about 5:00, not realizing how the piece had played out prior to that. In case anyone is puzzled.