Clock sync problem?

[Takashi Iwai]

On Sun, 07 Jun 2020 15:39:59 +0200,
Laurence Tratt wrote:
> 
> Hello,
> 
> I've found an interesting issue with an SSL2+ audio interface -- it plays and
> records fine (and, for the money, the sound quality is excellent!), but
> recording slowly but surely drifts over time. For example, if I record a
> click track in Audacity (or Ardour), play it through the interface and record
> it, and then line up the start of the recorded click track with the original,
> the two tracks will be around 5ms out of alignment after 30s. Interestingly,
> this problem does not happen with OpenBSD, where the two tracks line up
> precisely.
> 
> My guess is that the problem is to do with implicit feedback in endpoints. I
> wondered if the problem was the same as with the MOTU M4, but enabling that
> quirk for the SSL2+ introduced some crackle, but didn't change the drift.
> 
> I'm attaching a) the alsa-info file b) output from OpenBSD's kernel with
> debugging in the USB audio driver turned on in case that gives some clues as
> to what the two OS's and drivers might be doing differently. If anyone has
> any suggestions for how this problem might be addressed, I would be very
> grateful!

The recent change in USB-audio might help for a case like yours. 
Try my sound git tree (for-linus branch) or Linus' tree.  The former
should be pullable onto 5.7 kernel cleanly.


thanks,

Takashi