Old 09-14-2019, 12:47 AM   #1
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Default Reaper performance decrease if buffer size increase


I've got old but still reliable RME 9632. When I set buffer size above 1024, Reaper performance decrease and also CPU load is bigger. It's funny, because only 1024 buffer size is "sweet spot" between CPU load and Reaper performance.

Anyone knows why bigger buffer size (> 1024) causes lower Reaper performance and bigger CPU load?
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Old 09-14-2019, 07:01 AM   #2
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There's either something in how the driver the device is using is written or a hardware cache limit in the device itself that makes 1024 samples the max size supported. Going over that makes the system work harder to manage the non-optimal larger buffer than it would to make the latency at a lower block size.

My MOTU 828mk3 interfaces have a max supported block size of 1024 samples. My Apogee Rosetta has a max of 1024 at 96k or 88.2k and a max of 512 at 48k or 44.1k. Setting larger will just use more CPU cycles and can even crash the driver.

I believe 1024 samples is a typical largest supported block size. This isn't a published spec though. Similar frustration as for plugins that don't publish their minimum required latency. Up to the user to find out by trial and error.
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Old 09-20-2019, 02:10 PM   #3
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I reported several months back that I had similar issues with my Motu828. Weirdly, the larger the buffer size past 256, the worse performance I had. I get better performance on a larger session (50+ tracks, 100+ plugins) at 128 than I do with 512...which wasn't so with an older system and Roland soundcard.
i7 8700k,4.9Ghz,Win10,Reaper 5,Motu 828es,MJE Hulk 990,GAP Pre73/EQ81
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