Random crackles at low CPU usage (doesn't happen in Ableton)

[Jonek2208]

Hello,
I have a problem with Reaper while using it for live playing. I can play at quite high CPU usage without any crakles, but when I play quite normally then at totally random moment I can hear a short crackle, which is very annoying. When I tried similar setup in Ableton Live Lite I couldn't notice any crakles. Normally I would just use the Live Lite, but unfortunately my Akai Midimix button lights cannot be mapped using simple mapping, so I would have to write Custom Surface Controller, which won't be as flexible as ReaLearn. Another reason for using Reaper is the possibility of disabling the UI in VST which makes possible mapping strange parameters.

My laptop is Thinkpad P50 on Windows 10, CPU i7 6700hq, 24 GB ram, GPU NVIDIA quadro M1000M 2GB vram. Audio interface which I use is Behringer UMC404HD.
My rig contains of three layers: piano, epiano and pads. For pianos I use Pianoteq and for pads I tried both LABS and Xpand!2. Pianoteq as it uses modelling can be quite CPU consuming if you play a lot of low notes with sustain pedal pressed. I noticed (that's probably obvious for you) that Reaper CPU usage meter works in a completely different way. If Ableton doesn't hit 100% the system meter shows much less usage, while Reaper shows value which is very close to real Realer's CPU usage. I heard that Ableton uses only one core per track, so that's the reason why I can make CPU overflow in Ableton while in Reaper it is impossible, because it allows to use multicore rendering for VSTs.

I made all of the adjustments which mschnell described in his post. I disabled all unnecessary startup apps, CPU trothling, USB devices disabling, and still I can notice this issue. It looks like it's not a performance issue, maybe Ableton works better audio drivers or it has some kind of redundancy, so there are no sound issues as long as CPU meter is below 100%?
Big thank you in advance for anyone who will be able to help me.

Edit:
Well, all the tweaks didn't seem to help, so I finally gave up - I switched to Linux

[pepe44]

Did you get better result using Linux on the same machine ?

[mschnell]

AFAIK, this Audio interface is rumored for not being great for live playing due to bad latency (supposedly due to the drivers) .
-Michael