Nucleus + rev b with Roon supplied 1TB SSD
Buffalo Technologies BS-GS2016 switch
Nucleus + connected to switch via Ethernet cable
Auralic Aries G2.1 connected to switch via Ethernet cable
Mola Mola Tambaqui DAC connected to Auralic Aries via USB cable
1500 tracks on internal SSD
My Tambaqui DAC will accept up to DSD256 files so Roon Device Setup is set to max sample rate = DSD256
However I have several DSD512 files, which I want down sampled tonDSD256.
In MUSE if I Enable native DSD processing;
A DSD512 file is down sampled to DSD256, but the file only plays for 20-30 seconds before playback stops with a message “An audio file is loading slowly…”
If however both the Enable native DSD processing function is turned off, DSD512 is down converted to PCM 352.8/32 and that file plays without any interruption.
Note that this more processing intensive solution requires Processing speed = 5.3X. Whereas a more straightforward down conversion to DSD256 requires a Processing speed = 0.9X until it stops working. Note that I think my DAC sounds better with DSD files versus PCM file.
So, why doesn’t down sampling to DSD256 work?
I bought a Nucleus + for the extra processing power. Turning on and off the Parallelize function does not make a difference.
You are trying to perform two separate sample rate operations at 22 MHz and 11 MHz, respectively. Processing speed shows that you do not have enough processing power. Everything has a limit.
AJ
What @WiWavelength says, but note that you seem to misinterpret the processing speed indication - lower numbers equal higher load and vice versa.
So theoretically, a processing speed indication of 1x would suffice to handle the given task, but practically you’d need at least 1.2x to keep the stream going.
Processing speed is an indicator of realtime performance/throughput. The lower the worse it is. Below 1 means less than realtime so you get dropouts. You really need a minimum of 1.2 to have headroom. Processing speed varies dependant on not just cpu but network conditions if not local storage and other factors. Native DSD processing is the most intensive process Roon does and there are limits even for the Nucleus +. In some cases you just need a desktop CPU to handle the big stuff.
If you only have a limited number of albums in DSD512 format, I would recommend to downsample them offline. There are software programs like dBPoweramp that can do this rather easily.
(dBPoweramp Reference has a trial period of 21 days, but I don’t know if all functionalities are fully available in trial mode - you can always give it a try.
Thanks for all of your helpful responses.
Now I understand the definition of Processing Speed.
Just one curious fact, I also own a Nucleus+ rev a which I bought when they were first introduced in 2018 and use in another system. It has no problem downsampling 512 to 256. I guess newer isn’t always better.
For me and my stereo higher resolution DSD files sound better even if the original source was a lower resolution. I think I’m going to have to search for a DAC that can process 512 files 
Are they both accessing the same files? Are they local to the Nucleus that’s failing to downconvert or over the network?
My older rev A Nucleus+ is in a different geographic location with similar streamer, DAC and switch.
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