[LAU] Dual Delta Setup
fons at linuxaudio.org
Thu Jan 3 00:05:55 UTC 2013
On Wed, Jan 02, 2013 at 03:35:17PM -0800, Len Ovens wrote:
> After some thought, I am thinking this may be the issue, at least with
> delta series IFs. They use phase locked loops for both word clock and
> S/pdif. From some of the comments I have heard/read these are medium
> quality devices and "in sync" may mean some wandering on the slave device
> (voltage regulation is poor and heats the card for example). This could
> mean that the interrupt timing on the slave could move from preceding the
> master to lagging at the phase lock hunt rate.
Rather improbable. If the PLL on the SPDIF wouldn't work OK, you
wouldn't be able to input SPDIF in the first place. It takes more
than sample accuracy to clock and read the bits correctly.
Imagine that the counter and logic that define a period already start
running on the card when ALSA sets the HW parameters (i.e. before the
start command). And then, instead of resetting that logic and starting
a period exactly when the start command is given, the card simply enables
the interrupt to the PC. There will be a random delay between the start
command and the actual start of the first period.
For a single card things would just work. But it would be impossible
to sync two of them properly.
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
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