[vfio-users] Stuttering audio when passing through USB controller

[Bronek Kozicki]

On 03/02/2017 19:53, Tmplt wrote:
> I saw on an older thread here that passing a USB controller through and
> using a USB soundcard through it solved that users audio issues. I tried
> that myself by adding
>
>     <hostdev mode='subsystem' type='pci' managed='no'>
>       <source>
>         <address domain='0x0000' bus='0x00' slot='0x14' function='0x0'/>
>       </source>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x02'
> function='0x0'/>
>     </hostdev>
>
> to the .xml-file, but I can still hear frequent audio stutters akin to
> my quoted thread. Am I passing the controller incorrectly? The device
> I'm trying to play through is a FiiO e10k DAC which works without issue
> on the host and on bare-metal Windows 8.1.


More likely your Windows guest is suffering from large latency, since 
most USB DACs have small buffers and require (relatively) precise timing 
of audio stream sent from the USB port. You can check this by comparing 
http://www.thesycon.de/eng/latency_check.shtml and 
http://www.resplendence.com/latencymon when running on guest vs. bare 
metal .

If you are running nvidia card, then disabling PowerMizer might help , 
see this thread 
https://www.native-instruments.com/forum/threads/solved-dropouts-cracks-pops-on-windows-7-and-nvidia-gfx-card.126080/ 


You may also want to disable hypervisor CPU policy, as documented by 
Alex here 
http://vfio.blogspot.co.uk/2016/10/how-to-improve-performance-in-windows-7.html 
. This setting worked on my Windows 10 guest to significantly reduce its 
latency, its applicability is obviously not limited to Windows 7 only


B.