Hi all — I’ve been digging into a repeatable issue where my webcam’s built-in microphone drops out completely in a Windows 11 VM.
Everything works perfectly until I join a live Teams meeting — at that moment, the mic instantly disconnects and Teams reports “microphone not connected.”
The webcam itself (video) stays active.
This is 100% reproducible.

Note: I have used ChatGPT to help me summarise the steps I have gone through, but this has taken many days of messing about with LatencyMon, MSI_Util_v3, XML editing and even buying a USB 2.0 backplate to hang off the USB 2.0 spare header. Needless to say , booting baremetal with W11, the Webcam and Mic work flawlessly.

System

• Unraid: 7.1.4

• Motherboard: ASRock Z790 Steel Legend WiFi (single xHCI controller)

• CPU: i7-14700K

• GPU passthrough: NVIDIA GTX 1080 Ti (MSI mode)

• VM: Windows 11, VirtIO SCSI + Balloon (MSI-X)

• USB Controller: Intel Raptor Lake XHCI (8086:7a60)

• Audio / USB Devices:

  • Kodak Access Webcam (video + mic, UVC composite)

  • XMOS USB Audio 2.0 DAC

  • Ugreen USB Audio dongle (added later for testing)

Behaviour

• Teams “Test Call” → ✅ works fine (both mic + video)

• Join external meeting → 🎤 mic immediately disappears (“unavailable”)

• Mic re-appears only after VM reboot.

• LatencyMon shows DPC latency spike in ntoskrnl.exe right when the dropout occurs.

• WhatsApp Desktop shows the same pattern.

Steps Taken

1. Enabled MSI interrupts for GPU and all VirtIO drivers.

   

2. Ensured power management was off for usb devices

3. Tried both exclusive and non-exclusive modes for the mic in the windows sound settings

4. Increased VM memory from 16 → 32 GB; disabled Windows memory compression.

5. Confirmed VirtIO SCSI + Balloon using MSI-X.

6. Removed static USB <address> assignments in XML to allow dynamic enumeration:

   <hostdev type='usb' managed='yes'>
     <source><vendor id='0x0c45'/><product id='0x6366'/></source>
   </hostdev>
   

7. Investigated USB topology with lsusb -t:

   • Initially webcam + DAC were on the same ASMedia 2074 hub → one transaction translator.

   • Added a USB 2.0 backplate connected to motherboard header USB_1_2.
     After reboot, webcam and DAC now appear on separate branches of the Intel xHCI root hub.

   • LatencyMon greatly improved, system smooth, but dropout still happens on Teams join.

Current Setup

• Webcam and XMOS DAC now isolated under different branches (lsusb confirms separate 480M/12M paths).

• Using XMOS DAC for output and webcam mic for input.

• Planning to test with Ugreen USB Audio dongle + wireless mic to separate audio path fully - but would prefer to keep the single Kodak webcam with Mic.

Are there known issues or tuning parameters for UVC composite audio endpoints (isochronous USB Audio + Video) under vfio passthrough on Intel xHCI controllers?
The webcam mic works for local audio tests but always fails on real Teams meetings.
Any QEMU 8.x or kernel 6.x parameters (e.g. qemu:commandline tweaks, usb-native options, etc.) recommended to improve isochronous timing stability in such cases?

Reference

• lspci | grep usb → Intel 8086:7a60 (xhci_hcd)

• lsusb → Kodak video 0x0c45:0x6366 + audio 0x8087:0x1041

  • Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

    Bus 001 Device 002: ID 0781:5567 SanDisk Corp. Cruzer Blade

    Bus 001 Device 003: ID 174c:2074 ASMedia Technology Inc. ASM1074 High-Speed hub

    Bus 001 Device 004: ID 174c:2074 ASMedia Technology Inc. ASM1074 High-Speed hub

    Bus 001 Device 005: ID 1a86:8091 QinHeng Electronics USB HUB

    Bus 001 Device 006: ID 1b1c:1ba4 Corsair CORSAIR K55 RGB PRO Gaming Keyboard

    Bus 001 Device 007: ID 26ce:01a2 ASRock LED Controller

    Bus 001 Device 008: ID 0c45:6366 Microdia Webcam Vitade AF

    Bus 001 Device 009: ID 20b1:30c8 XMOS Ltd USB Audio 2.0

    Bus 001 Device 010: ID 8087:0032 Intel Corp. AX210 Bluetooth

    Bus 001 Device 011: ID 8087:1041 Intel Corp. KODAK Access Webcam

    Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub

    Bus 002 Device 002: ID 174c:3074 ASMedia Technology Inc. ASM1074 SuperSpeed hub

    Bus 002 Device 003: ID 174c:3074 ASMedia Technology Inc. ASM1074 SuperSpeed hub

    Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

    Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub

• lsusb -t

Note. There appeared a similar issue a while ago.

https://forums.unraid.net/topic/123447-intermittent-usb-mic-cut-out-pcie-usb-controller-passthrough/

But no apparent resolution, however, it does appear I have the same core symptom pattern:

• USB audio (often part of a composite UVC device) works fine for casual use or short tests,

• but under real-time streaming load (Teams, Zoom, Discord, etc.) the isochronous audio endpoint flakes out,

• and it happens even on dedicated PCIe USB cards when passed through to a VM.

That reinforces a theory that this isn’t bandwidth or hub-power related — it’s a timing and host-controller emulation problem in how VFIO hands isochronous transfers off to the guest.
It’s probably tied to:

• how QEMU’s xHCI emulation (and vfio mapping) handles “microframe” timing,

• or how Windows’s UVC driver reacts when a few milliseconds of sync data are lost.

The fact that mine behaves perfectly until a Teams meeting join event (which kicks off full-duplex A/V) and then immediately drops the mic fits that exactly.

Thanks in advance — I’ve tried to rule out everything from topology to interrupt latency, but this still feels like a composite-device timing issue specific to passthrough.

nas-diagnostics-20251021-2339.zip

Edited October 21, 2025Oct 21 by Bob_C
LSUSB format added msi screenshot

I had this issue and what I did is to using the udev blacklist rule: here

1 hour ago, PUNGGOKERS said:

I had this issue and what I did is to using the udev blacklist rule: here

Thanks for that. I will give it a go. If it works, I'll find some superglue to put my hair back in place!

Did this solve your issue?

It improved the situation but not entirely. Coincidentally I booted to my baremetal W11 on NVMe and although I had no previous issues using the Kodak Webcam, in this instance I opened Teams and the Mic disappeared for a moment (Mic disconnected message) and then reappeared a few moments later on its own. Beginning to suspect it may be a webcam quirk and although a baremetal W11 might be able to cope with it, even with udev rules, it looks like perhaps QEMU struggles with it in passthrough.

For now I have resorted to using a Ugreen USB audio adapter and connecting a wireless mic on the 3.5mm jack. That appears to work well on the same backplate connection.

So it does look more like a hardware issue with the vid and audio devices being in the same unit and not quite keeping it together.