Streaming audio via USB port

[KenHorse]

I've been experiencing audio dropouts using a CM119 CODEC device with a guest running Debian 10. I am also running ProxMox 8.0.3

I am thinking this is occurring because the USB port being used is being "time shared" by the host?

 

[Moayad]

Hi,

Can you try to connect the USB to a different USB port and see if the audio dropouts persist? or connect the USB audio to a dedicated USB port.

FYI, if you're using SPICE on the Debian VM you can add an audio device as described in our official document [0]


[0] https://pve.proxmox.com/pve-docs/pve-admin-guide.html#qm_audio_device

 

[KenHorse]

Hi,

Can you try to connect the USB to a different USB port and see if the audio dropouts persist? or connect the USB audio to a dedicated USB port.

FYI, if you're using SPICE on the Debian VM you can add an audio device as described in our official document [0]


[0] https://pve.proxmox.com/pve-docs/pve-admin-guide.html#qm_audio_device

I've tried different physical USB ports, virtualizing the port to the VM by both device # and vendor ID and no change

 

[KenHorse]

Revisiting this.

I've tried setting up SPICE in the Debian VM that experiences the dropouts but the USB device doesn't seem to be active from within the VM. I admit I'm not experienced with SPICE so it's probably something I'm doing wrong.

Other than selecting SPICE when setting the Hardware in the VM, what else must I do?

 

[Moayad]

Can you please post the VM config in order to see if there is anything not correct `qm config <VMID>`?


https://pve.proxmox.com/wiki/SPICE

 

[KenHorse]

root@ParrettPVE:~# qm config 100
boot: order=scsi0;ide2;net0
cores: 2
cpu: x86-64-v2-AES,flags=+aes
ide2: local:iso/debian-11.5.0-amd64-netinst.iso,media=cdrom,size=382M
memory: 2048
meta: creation-qemu=8.0.2,ctime=1694651843
name: ParrettASL
net0: virtio=86:EF:26:A7:D2:A8,bridge=vmbr0,firewall=1
numa: 0
ostype: l26
scsi0: local-lvm:vm-100-disk-0,cache=directsync,iothread=1,size=32G,ssd=1
scsihw: virtio-scsi-single
smbios1: uuid=9e29a938-25a1-4227-a14e-4bef5b5fb430
sockets: 2
usb0: host=0d8c:013a
vmgenid: a020957c-85d3-43f9-ab33-67ab2d3ba31d

 

[KenHorse]

Any ideas?

 

[KenHorse]

Oh well

 

[KenHorse]

After listening more carefully (and running usbtop in order to monitor the stream), I find that "dropouts" isn't exactly accurate in that no packets are being lost but only delayed. So a word of the sound file may stop mid-syllable only to continue where it paused, anywhere from a hundred milliseconds to perhaps a few seconds. Again, no speech is lost, it is only delayed for a while.

Does this additional info point towards anything in particular?

 

[leesteken]

In my experience USB passthrough is not suitable for low-latency (audio) or high-bandwidth applications (storage, video). PCI(e) passthrough of an entire USB controller usually fixes this but that comes with a whole new set of caveats.

 

[KenHorse]

I will check my hardware support IOMMU (it should as it's an Intel i5 processor) and I don't need to share USB with any other VM (nor the host). I'll see if this is a workable solution. Thanks for the idea.

One question I'm not clear on in the docs. Do I need to enable IOMMU in the host or VM?