[libvirt-users] Audio in Windows 10 VM is distorted. Using ALSA.

[Aleksei]

I don't have a solution, but please post yours if you find one. I've 
been trying to get a working sound out of my Windows 7 VM for a while 
now, every sound card available in libvirt produces just noise and 
crackling.

Maybe it would be great to have a virtio sound card. Things are 
apparently not going so well with emulating real hardware.


/--Regards, Aleksei/

------------------------------------------------------------------------

*From:* Manuel Ullmann
*Sent:* Tuesday, December 20, 2016 5:41AM
*To:* Libvirt-users
*Subject:* [libvirt-users] Audio in Windows 10 VM is distorted. Using ALSA.
> Hi,
>
> I can’t seem to find a solution for my last VM issue.
> I have distorted sound, when I play the Windows 10 device test
> sound. Only the Windows sound is affected. Mpd of the host is playing just fine
> meanwhile. I am using ich9 as emulated card, which is detected and
> installed correctly. The VM is using vfio-igd passthrough, so  vnc or
> spice are not used.
> I tried to match the Windows driver configuration, which only supports
> 16 bit output. I have a 24 bit USB headphone amplifier, which does not
> support it (S32_LE only). Trying direct playback on the PCH card jack
> did not help though.
>
> The headphone amplifier is connected via optical Toslink, so there is
> standard snd_hda_intel output used (snd_usb_audio is not involved).
> Passing the USB part through I get much clearer output, but still have
> popping sounds. Googling around, they seem to be quite common on Windows
> 10, although I had it working fine on two bare-metal machines.
>
> I have tried fixed settings matching the ones of the dmixed device
> too. Don’t know, what is polled with enabled poll option. I also tried
> sdl and pulseaudio, which did not help. For the latter not so surprising
> since it is an Alsa pipe. The former was worse.
>
> The goal of this setup is having the same playlist state on both
> systems and using the better audio framework for music playback (Windows uses
> too much software layers). Of course the popping sounds on audio device
> passthrough also would be annoying, but that might be a different issue.
>
> Best regards,
> Manuel
>
> used alsa device:
> pcm.dmixed {
> 	type asym
> 	playback.pcm {
> 		# See plugin:dmix at http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html
> 		type dmix
>
> 		# Don't block other users, e.g. the Timidity midi-player daemon
> 		# http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html
> 		ipc_key_add_uid false
>
> 		ipc_key 1025
> 		ipc_perm 0660
> 		ipc_gid audio
>
> 		# Don't put the rate here! Otherwise it resets the rate & channels set below, as shown by:  cat /proc/asound/card0/pcm0p/sub0/hw_params
> 		slave {
> 			# 2 for stereo, 6 for surround51, 8 for surround71
> 			channels 2
> 			pcm {
> 				format S16_LE
> 				#format S32_LE
>
> 				#rate 44100
> 				rate 48000
>
> 				# http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html
> 				# Maybe helps
> 				nonblock true
> 				type hw
> 				card "PCH"
> 				device 0
> 				subdevice 0
> 			}
>
> 			# mplayer2 chooses 1024
> 			# period_size 512 with buffer_size 16384 stops crackling in xmame
> 			# 320 breaks flash - https://bbs.archlinux.org/viewtopic.php?id=129458
> 			#period_size 512
> 			period_size 1024
>
> 			# 4096 might make sound crackle
> 			# mplayer2 chooses 8192. Half-Life 2 chooses 16384.
> 			# If too large, use CONFIG_SND_HDA_PREALLOC_SIZE=2048
> 			buffer_size 8192
> 		}
> 	}
> 	capture.pcm "schneeball"
> }
>
> libvirt xml snippets:
>
>      <sound model='ich9'>
>        <address type='pci' domain='0x0000' bus='0x00' slot='0x09' function='0x0'/>
>      </sound>
>      ...
>      <qemu:env name='QEMU_AUDIO_DRV' value='alsa'/>
>      <qemu:env name='QEMU_DAC_FIXED_SETTINGS' value='0'/>
>      <qemu:env name='QEMU_DAC_TRY_POLL' value='0'/>
>      <qemu:env name='QEMU_DAC_TIMER_PERIOD' value='0'/>
>      <qemu:env name='QEMU_DAC_BUFFER_SIZE' value='0'/>
>      <qemu:env name='QEMU_DAC_PERIOD_SIZE' value='0'/>
>      <qemu:env name='QEMU_DAC_DEV' value='dmixed'/>
>
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