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Old 06-26-2019, 12:33 PM   #8
JamesPeters
Human being with feelings
 
Join Date: Aug 2011
Location: Near a big lake
Posts: 3,943
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So I recently realized what I'd done with RTIRQ wasn't doing anything. I had to run (sudo) "rtirq start". Then I checked using rtirq status and I could see the RTprio become what I specified.

Anyway after I set the audio device to 95, I was able to lower my latency to the lowest I've ever done it, just over 4ms round-trip (and confirmed, not just the reported latency) at 44.1 KHz. 6 blocks of 32 samples is the setting I can now use, and it's stable up to 100% CPU. Lol.

Another thing I realized though: setting the RT priority that high for the audio device isn't necessarily all good. When the CPU is being stressed hard, to prevent xruns it means Reaper starts acting less responsive (moving faders, for instance). That's ok, but there's a "middle ground" where you're just using the CPU "a fair bit" and maybe you want the controls to be more responsive. Setting audio device RT priority at 70 for instance seems like a nice compromise of being able to get the lowest possible latency and also good responsiveness even when the CPU is being slammed with lots of plugins (at the expense of the odd xrun). Then when I set my buffer to 4 blocks of 128, it's solid up to 100% CPU and responsive.

Note: I'm using ALSA in Reaper. In the audio device settings dialog, there's a setting to change the RT priority.

Also I played around changing Reaper's (ALSA) RT priority. It seems keeping it lower than the audio card's RT priority means fewer xruns when you're pushing things to extremes (super low latency and highest CPU use), but Reaper feels less responsive at the same time. If you increase Reaper's (ALSA) RT priority it will be more responsive but then it can have more xruns. I tried setting the audio device's RT priority to 95 and Reaper (ALSA) RT priority to 80 (then 70, etc.) but it seems the best balance was to keep Reaper (ALSA) RT priority around 40 as recommended in the settings dialog (then put the audio device's RT priority around 70).

Last edited by JamesPeters; 06-28-2019 at 08:38 AM. Reason: Clarification that I'm using ALSA in Reaper
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