what sample rate are you using for your projects?

sorry but VST or computer problem isn't gear... nevermind much but it looks like you are using slightly more plugins than your soundcard and computer can handle.

Thanks and sorry for being in the wrong place... thought that audio interface was a gear
To Ruud: 24bits 48000Hz. my audio interface is Mbox 2

@Fanzio I think you should check the performance of your.computer. It might be overloaded... 48 K Sample rate should not produce an issue... probably it is time to upgrade your processor...

and yes... I think... if we talk about audio interfaces or computer... we are talking also about gear....

The problem with the crackles is most of the time CPU related. It is an ASIO overload. That means your CPU can’t handle the operation fast enough. You can work against that by setting a higher buffer size (or in some Interfaces amount of samples) in your ASIO driver. That results in less crackles but higher latency. It is recommended to track at lower buffer size and mix at a higher buffer size. Or just buy a beast of a cpu :D
And for the Audio Interface on performance topic... A better DSP or built in GC could give you a slight benefit but the audio interface is more important for the good quality of the signal. Good preamps, low noise floor, good set of I/Os and analog to digital converter etc. but the cpu and ram is the most important thing when it comes to performance in music production.
Hope that was helpful. Cheers!

thanks a lot Ruud and Phil! The problem of my ASIO is that it is old (2011) because the Audio Interface is old (2007) and i am stuck to a buffer size of 256.
I tried with Asio4all, and it got Reaper crash in some cases...
As my computer is new from 2020, i thought it could be on the Audio Interface side (VSL told me to update my Audio Interface drivers, but there is no update since 2011...).
Thanks anyway, will continue to investigate and update if i find a solution.
Cheers

If there is no recent driver for your Interface from the manufacture would recommend getting a new Interface. Even if the Interface and the ASIO Driver might not be that important when it comes to speed (which you need to avoid ASIO overloads), they are definitely very important when it comes to stability and quality. A recent ASIO driver is crucial for working without headaches. Cheers

Thanks ! will do !

Just had my Audio Interface changed and the problems which occured with a lot of instruments/reverb vanished, BUT, I now get sound cuts every 10-15 seconds.
So I guess there is a general problem with my PC as well.
Do you know a list of things to check/do to optimize a pc for sound production ?

If anyone is interested, i solved my problems by twicking the PC using this list from Steinberg. Can not remember exactly from which step it was solved, i think around USB twicking.
https://helpcenter.steinberg.de/hc/fr/articles/360008589880-Windows-10-How-to-set-up-and-optimize-a-Digital-Audio-Workstation-DAW-