Hi, I have searched the forum up and down and there have been quite a few threads about this (or something similar) over the years but I haven't been able to find a solution that works for me. And I've tried all I could find...
I'm running Reaper x64 5.961 on Win10 Pro, i7 7700K, ASUS Z170-A, 16 GB RAM, Fireface UFX+, Nvidia 1050TI GPU, all the latest drivers, only SSDs for OS and audio. This system is heavily optimized for audio and apart from this issue is perfectly capable of running the most demanding mixing sessions at low latency with tons of plugins and lots of outboard gear (using ReaInsert). I'm running everything at 88.2kHz, no re-sampling.
This only happens with record-armed instrument tracks - for me so far with Kontakt 5.81 and Superior Drummer 2 and 3. Average CPU usage in these cases can be very low or very high - doesn't matter, the crackling is always the same. RT CPU is low when record-arm is off and much higher (up to 60%) when it's on. Plugins are 64-bit only, no bridging at all.
As soon as I disable "Record-arm", the crackling goes away. It also stops crackling, when I select another track and "Automatic record-arm when track selected" is enabled on the previously selected track. Obviously, in these cases I'm not able to preview sounds using the MIDI keyboard. That's why it's not an option to turn it off completely.
Here's what I've tried so far:
- Disabled Speedstep (EIST and others) both in BIOS and in Windows power options - no change
- Enabled/disabled anticipative FX both globally and on a per track basis - no change
- Enabled "Allow live FX multiprocessing" - crackling gets much worse, regardless of the number of cores
- Increased latency up to 2048 samples (I'm usually running at 256) - less crackling but still noticeable
- tried the UFX+ both with USB3 and Thunderbolt (usually TB) - no change
- tried a small test project that crackles on the aforementioned PC (only NI Kontakt and 2 instances of Massive used) on my Lenovo laptop using the same UFX+ over USB3 - crackles are exactly the same
- the very same test project does not crackle at all when I'm using a crummy Focusrite 6i6 as audio interface.
- with that in mind I've tried to lower the number of inputs and outputs from usually 54 channels each to just a stereo pair - no change
- tried the same test project at 44.1 - no change
- enabled "MMCSS for ASIO" in the USB settings of the Fireface (this option doesn't exist in the TB version) - no change
- installed "portable" Reaper into new folder and tried again with default settings - no change
- uninstalled the latest graphics driver and tried one from a year ago - no change
The test project shows an average CPU usage of 2~3%, RT CPU is about 1.5% with input monitoring off and about 25% when enabled.
It seems the only common denominators are Reaper's "record-arm" and the UFX+. As drivers from RME are usually top-notch, I suspect there's something inside of Reaper that's not playing nicely with the Fireface. Are there any settings in the Preferences (or wherever) that I can try to solve this?