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This is the last version for now, I think. I slow the piece down by a small amount every 40 seconds until it is running around 11% slower at the end. Each of the 12 tempo reductions are done by the ratio of 2^(1/72), which is the 72nd root of two (1.0096735332). The beats per minute are divided by that number 12 times. Coincidentally, that’s the same as the ratio of one note to the next in 72-EDO, the tuning the piece is realized in. I can’t figure out how that happened, but there it is.
Csound takes care of tempo with the t tempo statement.
t0 1200 800 1200 896 1188 1592 1188 1688 1176 2376 1176 2472 1164 3152 1164 3248 1152 3920 1152 4016 1140 4680 1140 4776 1129 5432 1129 5528
1118 6177 1118 6273 1107 6915 1107 7011 1096 7645 1096 7741 1085 8368 1085 8464 1074 9084 1074 9180 1063 9792 1063 9888 1052 10493 1052 10589
The t0 makes it a tempo statement. The next number is the beats per minute, in this case 1200. A quarter note is about 8 beats when there are 1200 beats a minute. The next number after beats per minute is the number of beats where the next tempo marker is found, in this case 1200. So it stays at 1200 beats a minute for 800 beats, about 100 eighth notes. The next number 896 is the beat marker, and 1188 is the beats per minute. 1200 / 1.0096735332 is 1188, approximately. Over the next 96 beats or 12 eighth notes, it slows down from 1200 to 1188 beats per minute. Then at beat 1592 it starts to slow down to 1176 beats per minute, arriving at that speed at beat 1688. The overall effect is a gradual slowing down, sometimes noticably, sometimes imperceptively, until it stops.
