Clock sync problem?

[Takashi Iwai]

On Mon, 08 Jun 2020 10:32:24 +0200,
Thomas Ebeling wrote:
> 
> 
> On 08.06.20 09:19, Takashi Iwai wrote:
> > 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.
> >>
> > 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.
> 
> Since I recently had clock drift issues with Audient devices, I'm
> intrigued by this. @Takashi Can you quickly elaborate, what you think,
> Laurance's issue might be and what has changed in that tree that might
> help him fix it? Is there some general issue with the current (stable)
> sound/usb implementation?

The frame size calculation in USB-audio driver wasn't accurate enough
because of the computation in Q16.16 format.  It works OK for async
mode, but for others, it can accumulate rounding errors.  The recent
change corrected it for a more precise way.


Takashi