Bud - on my late 2015 iMac 21.5 (2.8ghz i5, 8gb ram, 750gb hdd, Iris Pro 6200) RT generation takes exactly the same time on Big Sur as it does on Mojave (I don't have Catalina to test right now). Test song was the _BLUETAM demo song which has 5 RT's and is 12 bars and 5 choruses. RT generation took 14.394 seconds on Big Sur and 14.892 seconds on Mojave, which is only a 3% difference.

Some users like you have reported that RT generation is faster in Big Sur, and we have tested some faster RT generation on the M1 chip. It'll vary a bit depending on hardware though, as in my case Mojave and Big Sur were basically the same.


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