Re: [virtio-comment] virtio sound: add missing definitions for 12 and 24kHz sampling rates

[Manos Pitsidianakis <manos.pitsidianakis@linaro.org>]

Hello Andreas,

The spec says it is purposely modeled to be compatible with the HDA 
spec. HDA is optimized for specific multiples or submultiples of 44.1 
kHz and 48 kHz. Specifically, look at "5.4 Handling Stream Independent 
Sample Rates" and "Table 56. Defined Sample Rates". My (unexperienced) 
understanding of the following statement is that using such rates with 
controller hardware that is made for HDA will result in timing issues:

> This implies that the controller and link must also provide for an 
> exact sample-rendering rate at the codec, in order to avoid any long 
> term drift between sample delivery and rendering and the subsequent 
> over(under)-run of codec buffers.

https://www.intel.com/content/dam/www/public/us/en/documents/product-specifications/high-definition-audio-specification.pdf

If that is the case, I think the best approach would be to specify a 
non-HDA mode of operation to support more sound hardware. The most 
straight-forward solution though is for you to resample the audio before 
and after it goes through virtio-sound.


Regards,

-- Manos Pitsidianakis
Emulation and Virtualization Engineer at Linaro Ltd