Re: qemu modifies host audio sample rate with coreaudio backend to 44.1khz on startup

[Christian Schoenebeck]

On Friday, March 24, 2023 8:38:25 PM CET Frank Carmickle wrote:
> Greetings all,
> 
> Thank you Thomas for bringing this to the attention of folks who are in the 
> know.
> 
> Thank you, Christian for explaining.
> 
> What I am finding is that qemu sets the host to 44.1k even though alsa dmix 
> in the guest is set to 48k. What I wanted was to set the host to 96k and the 
> guest to 96k. When I do that, by using audio midi setup for the host, and 
> changing alsa dmix rate to 96k, after starting the guest, audio midi setup 
> shows that the host is set to 44.1k.
> 
> When using the parameter Thomas mentioned, the host sample rate is changed to 
> the designated.
> 
> Seems like alsa has a problem. I'll use Thomas's suggestion as a workaround, 
> for now.

DMIX in ALSA is like mixengine in QEMU: a layer that automatically converts
audio format on the fly between incompatible sides (sample rate, channels,
etc.). That's used if the audio hardware does not support the desired audio
format natively.

You did not mention which audio frontend (the virtual audio hardware emulated
by QEMU for guest) you are using. I just made a quick test with the AC97
frontend and `aplay` a wav file on guest, and it used 48 kHz like the wav file
content, not 44.1 kHz.

@Thomas: I just realized that QEMU's audio frontend selection parameters are
not documented at all?