Update 2.4.1 to 2.5.1, massive CPU hit, crackling.

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

1 Like

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

1 Like

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.

1 Like

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.

1 Like

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!

1 Like

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!!

1 Like

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).

I can’t afford a drop of performance now, I am waiting for good news on this community. :broccoli:

The CPU consumption has changed positively. I also had big problems with V2.51. After update V2.52, I have the impression that it behaves like V2.41. Good luck.


While using 2.5.2 for the first time yesterday, I noticed that the only place I experienced crackling where I had not previously, was while browsing the library.

1 Like

For me 2.5.2 has been on par with 2.4.1, so… happy times. (Thanks devs! :slight_smile: )

1 Like