What CPU should I buy for VCV Rack?

Hi , I’ve been lurking for a few weeks,having discovered VCV Rack via a video by @Omri_Cohen,which YouTube kindly served up as a suggestion. One of they’re best ever.

I’ve been needing a new PC for a good while,and now want to get the very best Rack performance that I can.Just 2 or 3 years ago it would have been Intel all the way,but recent AMD offerings have been winning plaudits even in the audio/vst world.

As an aside,I can hardly believe how little influence music/pro audio has in the PC world. ScanProAudio seem to be about it,when it comes to testing for audio.

So,I was pretty much set to buy an AMD 12core 3900x or 16core 3950x,until I read a post,here : [New PC Time - High Core Count / Zen2 Ryzen / AVX], from late last year. The OP,in that thread,@attheleash,had this to say,at the end : " there’s a massive performance hit when Rack utilises cores belonging to multiple CCXs" and “3900X is a 12 core processor with 4 CCXs (3 cores per CCX) - so it looks like any single VCV patch can only use 3 cores effectively on this setup”.

This leaves me very “curious” as to how Scan could have the 3900x/3950x beating almost all of the Intel CPU’s in both of their DawBench tests.

I know several people posted on the linked thread about having success with [8 core] Intel i7-9700kf machines.

Does anyone have any experience with the 12+ core Intel HEDT processors ?

The 14-core i9- 10940X looks like a real contender,here,at the same price as the AMD 3950x. Scan show the 10940x and 10960x slaughtering the 8 core Intel 9900k,but I don’t know if that counts for anything at all with VCV Rack.

Any help,and advice,on which CPU to buy,for the best VCV Rack performance,would be greatly appreciated.

Thanks in advance.

You will get a lot of people here who like the AMD. I don’t know how many people actually tune their cores, etc… Modern Intels work very well, too. You won’t go wrong with any modern CPU and a midrange gfx card.

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Hi, OP on that thread here…

My findings on cross-CCX efficiency in Zen2 still stand - however, I’ve not found it to be a practical limitation. The power that can be utilised in a single CCX is sufficient for pretty much anything I need to do in VCV.

As an example, this is my old polysynth patch, which is still the most heavy patch I regularly use in VCV:

3x surge osc, 3x vult freak, and a ton of routing and tone shaping

it’s running comfortably in about 75% of a CCX, clocking at ~3.5GHz (full-tilt speed would be 4.2+GHz)

that’s at 44.1KHz, 64-sample buffer

and every module in the patch is running at 16-voice polyphony

i’m not running any optimisations, overclocking at all. other than using process lasso to control application CPU affinity (i.e. locking VCV to a single CCX)

i can have other stuff (DAW, plugins, synths) running on the other 75% of the CPU :smiley:

i don’t know how well current intel HEDT is doing in comparison - but I feel no need to switch or upgrade, not in the slightest

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Oh nice :slight_smile: I don’t have any experience with AMD, but I think it’s important to mention that GPU is also an important part for getting VCV to work better, and also a decent audio interface.

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Hey Omri, What is your laptop specs ?

This is my laptop - Intel Core i7-9700K, 8x 3.6HHz, 12MB L3 Cache, 32Gb RAM, NVIDIA RTX 2060

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I’ve got a Laptop for travelling some weeks ago,

with a Ryzen 5 4600H (6 cores and 12 threads) and a Nvidia GTX 1650 mobile and 8gb ram,

it’s doing a real good job handling VCV and I haven’t yet met any limits in the patches I build.

you have beast of a machine. I am sure it will last for many years ahead.

I sure do hope so…

@attheleash, Thanks so much for your answer.That does seem like a very powerful ccx. I must admit,though,that only being able to use 3 cores,out of 12,for the most important software would drive me nuts.

Even when the the new VCV plugin arrives,I can’t see it solving the problem.You’re running your DAW seperately - not sure how,exactly.

It seems to me from weeks of research that the only way to take advantage of 4 seperate ccx’s would be to run 3 or 4 instances of VCV Rack simultaneously,all sync’ed together - each on a seperate ccx. Sync’ing the seperate clocks might not be too difficult,but making all the audio/midi outputs work together seems like a much more difficult problem,I think.

[I had hoped to figure out how to do this,and contact you with the info,so that you could utilize more ccx’s fof VCV,if you wanted to].

Any advice on how to do this,from anyone,would be greatly appreciated.

Thanks again for all your help.

@Squinky.Labs,Thanks.That’s nice to know.

Also,I love your modules,and think they look great,too.Clean design,and I love the blue that you use on the knobs and dials.Lovely modules,altogether.

@Omri_Cohen,Thanks,I think I’ll get a decent gfx card around the $200 mark.Hopefully that should power the Modular Fungi visual artworks [Opsylloscope and others],along with the Rack UI.

I mentioned you since I always like to give credit where it’s due.Great tutorials,mostly featuring fantastic music.That’s what got me really excited about all of this in the first place.

Seems I’m a Magic Mushroom,now.And,here,I thought I’d kicked all that crazy stuff long,long ago.

Also,you seem to run some pretty big patches on your i7 Laptop without problems,so that seems like a good pointer.

Thanks for all of your tutorials,both the great info,and the inspiration.

@rsmus7,Thanks.That’s great news,and very encouraging.I’m happy that it’s working so well for you.

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I really appreciate it man, thank you! I enjoy what I do and it’s great for me to know that other people also enjoy my work. Cheers!

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Thanks, that’s very good to hear. Within the constraints of being a bad visual artist (and not having much extra time) I try to make the panels as functional and polished as I can. That blue knob is/was actually a stock VCV component - I just latched onto that blue and beat it into the ground!

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I agree, it does seem somewhat counter-intuitive to limit the cores available to VCV so drastically. And it was a little disappointing to find this out after I’d bought the new system. But like I said, it’s not really had any practical impact for my usage

Just to clarify the performance hit when going cross-CCX - when running the above patch on 2 CCXs instead of 1, the CPU hit on both CCXs actually goes up by about 15% despite having twice as many cores! i.e. 1 CCX = ~70% usage, 2 CCXs = ~85% usage on both

As far as I’ve been able to tell, this is all to do with inter-core data latency. This diagram should show you all you need to know:

…so while, within a CCX, data latency is extremely low, almost twice as good as the Intel example (Coffee Lake Refresh), between CCXs it flies up, almost three times worse. And it indicates, to me at least, that any multithreaded application with intensive real-time non-block-processing DSP (e.g. VCV) should be restricted to running inside a single CCX on Zen 2 processors.

Whether Intel offer anything that gives you an increase in overall capacity (perhaps at a lower overall efficiency) with their newest HEDT chips is something you’d probably want to look into if you’re going for a pure-VCV system. Personally, VCV is only 1 part of my setup and I’m happy keeping it locked to a quarter of the CPU. It can still handle literally hundreds of modules.

The competing architectures are different enough now that you really have to go into a lot of detail about the nature of the applications you want to run - how they process and move data around, what processor extensions they leverage, how much power they need for a given scenario, how they spread load - before you can make the best decision on what to invest your money in. VCV, in my experience, is a very peculiar scenario to work with - normal, block-processing VST plugins don’t suffer this cross-CCX performance drop nearly as badly, having tried the likes of Diva and other multithreaded VSTs…

edit: I meant to add - I don’t think there is a way to run multiple instances of VCV on a single machine - the program stops you from doing this

Whether that changes when VCV runs under a VST host, I’m not sure, and perhaps more specifically, if it’s possible to tie instances of VCV running under a VST host to specific CCXs, also remains to be seen. Or even whether such a thing is necessary, as they will be processing in blocks (presumably)

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@attheleash,That’s quite some post.Thanks for all the thought,and detail,even diagrams. I was away from the computer,so couldn’t answer till now.

There’s a lot to mull over here.For instance,although I’m quite familiar with the VST world,I don’t remember ever hearing of block-processing vs non-block-processing,till now.But it would explain a lot about your results with Ryzen vs Scan’s results.

I have Diva and Repro1+5,and many other high quality VSTs,including Kontakt,and some expensive,high quality libraries,which I intend to continue using,though I plan on selling a lot of the synth and effects VSTs that I’ve built up,now.

I have a few more things to say,but can’t right now.I need to check a few things.

Thanks again for the very detailed post/reply. I’ll post again,shortly.

One quick thing - if Kontakt / Libraries are an important part of your setup, it may swing the balance more in favour of going Intel, as there is still generally an edge there where memory bandwidth is concerned, and Kontakt is mostly about pushing around lots of sample data from system memory. VCV, I should think, is very cache-intensive, which is why core latency seems to be more important there.

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@attheleash.Thanks again.You’re a veritable goldmine of information. I don’t know how much Kontakt vs VCV/Synths I’d usually use,but I have some great libraries,like Heavyocity Novo [strings],Forzo [brass] and Gravity,and quite a few others.

I’m not sure how well “cinematic and orchestral” will work with modular,but I’d like to find out. I’d thought of running my VSTs in VCV,using the VST Host module,which is very reasonably priced. It seems to me that the “generative”/sequencing capabilities of VCV could work brilliantly with Kontakt,and also with good VST synth and effects that I already have.Mind you,this is just hopeful speculation at this point.

I was just checking out the Intel 10900k [10 core/Ringbuss],and I think that shows a lot of promise,even though the Intel tech isn’t as shiny and new as AMD’s.

One other thing : Does VCV Rack really have something built into it that only allows one instance per computer ? That would seem crazy to me.Sync’ing clocks shouldn’t be any great problem.Don’t know about outputs though. Maybe Expert Sleepers software,and virtual audio cables,or even a multi-input audio interface ?

Anyway,thanks again for all your very helpful advice. This is my first real post on this forum,and I didn’t expect this amount of help.Seems like a great community,to go with the great software.

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That looks really interesting… I built it and it runs OK on my Mac.