Old 12-07-2019, 08:45 PM   #1
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Default RT SPIKES AND DROPOUTS - Please assist.

I'm getting major real time spikes and freezes on heavy projects. It's worst when opening or closing the midi editor, but also happens when stopping transport, and soloing or muting a track. If I select multiple midi parts and try to open them together it gets especially bad. I'll often get a major freeze for a few seconds, the RT CPU spikes, and a weird graphical glitch where the mixer on my second screen goes fuzzy and out of focus then refreshes (this weird graphical thing has been happening a lot since 6.0, it happens when autosaving too sometimes). The main issue is the RT spikes though.

Please see this gif (apologies that it looks a bit odd - trying to record two different res screens at the same time) - you can see I double click the midi parts, everything freezes, then when it unfreezes I get a big RT spike and dropouts in the audio, and it's just as bad when closing the midi editor, you can also see the fuzzy mixer refreshing that I mentioned (ignore the fx slots disappearing on the mixer, that's something to do with the gif recording).


I've tried rolling back, tried a portable install, tried disabling/enabling live processing on the midi editor, as well as the media buffering, makes no difference to the RT spikes, it doesn't happen on every project, but once it 'kicks in' it's a nightmare.

II know people will say it's a rogue plugin, but I've tried going through and disabling them in batches and there is no one plugin causing the issue, if I disable enough of them then the behaviour stops, but it's not one specific plugin - it happens when a project passes a certain threshold of FX use, and I think it's related to anticipative FX, and some of the issues raised here with APFX and complex routing - https://forum.cockos.com/showthread.php?t=225636

I expect someone will also note the high PDC amount on some of the tracks and say this is the main issue. I'm pretty sure it's not. I can make a test project with a bunch of reafirs and pro-q's in linear phase mode, get the PDC up to 20000, and none of these issues occur - I'd bet my hat that it's related to APFX, but if I turn off APFX then Reaper becomes woefully underpowered, so it's a tricky one. Hoping someone can help.
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Old 12-07-2019, 10:43 PM   #2
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I've been testing this more, and I should have mentioned there are quite a few nested folders in this project. I've noticed if there are plugins with latency on the folder tracks and I disable these, it makes the biggest performance difference in terms of these dropouts. I do think PDC may be more to blame than I initially thought. (doesn't matter if it's 32 samples or 500, because Reaper always adds a full 1024 samples for each latent plugin)

Removing tracks with high PDC chains helps the behaviour overall, but I'm also removing heavy FX by doing this, so it's tough to tell whether it's the PDC reduction that's helping, or just the lower strain on the CPU or APFX.

I also remembered other users posting about these issues regarding CPU issues with complex routing and latent plugins that need PDC... and I believe (can't find the thread now) that Justin actually confirmed there was room for improvement here and it would be looked into at some point.

I wonder, if we can get the full buffer per latent plugin issue addressed, then maybe this issue might become a lot more manageable?
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