Update 2.4.1 to 2.5.1, massive CPU hit, crackling.

@shofb , all previous installers are at listing directory /downloads/ (nope: see below) – a simple uninstall and reinstall should work. Baffling that the overhead is incurred even with no modules loaded. If I have time over the weekend I’m going to poke through the Github commits, compile some intermediate versions, and see if I can diagnose this, though I hope it’ll get fixed soon. If I find anything I’ll send observations over to support in furtherance of that objective.

Is anybody not having problems with 2.5.1? Also, I know 2.5.0 wasn’t around very long because of the ParamHandles bug, but is anybody willing to give 2.5.0 a try and assemble a few data points? If the problem exists in 2.5.1 but not 2.5.0, that’s a much smaller search space.

Hello Everybody, I installed 2.5.1 and so far don’t see any issues. My old patches work just as before the update - no CPU jumps, no audible crackles.

My computer is very old Lenovo ThinkPad X230: Intel(R) Core™ i7-3520M CPU, RAM 8.00 GB, build in Intel HD 4000 graphics (no GPU), Windows 10 Pro 22H2. external monitor 1920x1080. VCVRackFree 2.5.1, single tread, 10Hz framerate, WASAPI driver (48kHz/256ms).

Is it possible something to be related to the GPU handling ? Will be interesting to hear from another user with no dedicated GPU…

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I don’t see rack pro only rack free… will it update?

oh, good point, sorry–I just assumed both were in there.

If you log in to the website, look for the Rack Pro download link, and manually edit the version number, it should work (I was able to download 2.4.1 and 2.5.0 just now that way).

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I’m still waiting to update, I can’t handle a drop of performance on this PC until the end of June. finger crossed, then I will update.

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And what’s the CPU if you put a single audio module in the patch, and connect it to a working audio interface?

Since Rack user dir was moved you would first have to move it back again.

Could also just go to the Rack Development Blog where all versions are announced.


Much easier!

Thanks, good trick

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thx! I must admit that @LarsBjerregaard’s approach is better :slight_smile: – even though the posts say “pre-release” they’re the final versions and point to the same place

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I’ve noticed my i7 laptop struggling a bit more, and the fans coming on much sooner, usually immediately when I load VCV. One thing I realised is that upgrading seems to have set the frame rate back to the default 60Hz, dropping this down to 15 lowered CPU use by about 10% straight away, and also got the fans powered down…until I add a ton of modules at least! Another issue is I’m now getting this on any Reaper projects where I’ve used the Pro VST:


The update didn’t change the location of the VST plugin, so not sure why this is happening.

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Have you experimented with a dual architecture Rack installation, including renaming one of the Rack installs?

No not yet, apart from having 1.6 installed to run really old patches…

Ok, maybe I should have phrased it differently - the point is, if you want to run both 1.6 and 2.5.1 on the same machine, you need to decide which one of them you want to be able to use in the DAW, because you can’t use both. The one you want to use in the DAW must be installed last, and its directory and executable must not be renamed after installation, because that’s where the Rack DAW plugin will look for it.

Cheers Lars, I already had 2.4 VST so I’m not sure why it’s not recognising the update.

From looking at the changelog it seems that Andrew has fixed (or at least attempted to fix) the performance regression in the latest version 2.5.2.

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The relevant commit is interesting reading for anyone interested in C++ optimization. Hopefully we’ll see the new approach play out positively in the field!

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I only see about a 1.5% CPU diff between 2.4.1 and 2.5.2 with same patch, so yes, much better, but not yet same, if no 2.5.x features used…


Sounds good! 1.5% is probably in what I would call “measurement noise” and those numbers tend to bounce up and down a bit. Sounds roughly like “unchanged” to me and I think that’s the important bit. Of course, you could try and make a large and taxing patch, then measure on both versions, and see if you can make the difference consistently larger than that. If not I’d say job done.


for those of us (me) who is still on 2.4.1, should we still wait to upgrade? i cant afford any glitches right now!!


There are ways to keep two versions of Rack on your machine (previously posted on this forum, but I don’t have the reference for you), so you can keep your working setup and also experiment with the latest (now 2.5.2).