Re: [ecasound] capture from two delta 1010LTs at once

On Thu, 17 Nov 2005, Bery Rinaldo wrote:

> ecasound -t:10 \
> -a:1,2,3,4,5,6,7,8 -f:16,8,44100 -i:alsa,analog8_1 \
> -a:A,B,C,D,E,F,G,H -f:16,8,44100 -i:alsa,analog8_2 \
[...]
> As for the syncing of the two cards, it seems that S/PDIF is the way to go
> for the Delta 1010LT. I used the envy24control GUI to select S/PDIF In for
> the Master Clock for card 2 and set the "Locked" Rate State and connected the
> S/PDIF output from card 1 to the S/PDIF input on card 2. I ran the above
> capture command with the same analog signal (via a Y-cable) going to one
> input on each card. I then compared the signals in Audacity -- they were
> _very_ close -- I believe that the differences may be due to ADC differences
> between channels. I tried the same thing with two channels on the same card

The clock-sync is important to avoid clock-drift. This will avoid buffer
overruns that would otherwise happen sooner or later if the clocks were
not synced.

But it's important to note that clock-sync won't guarantee that the
devices are started at the same precise instant. As ecasound has to start
the devices separately, the device started first will be a few samples
ahead. ALSA provides mechanisms for triggering multiple devices at once,
but you need to use the ALSA "multi" (and possibly others, I don't have
experience with these) plugins to combine the devices, so that ecasound
will only see one device which it will trigger.

For many uses the small errors in trigger time will not be a problem
(clock-sync against drift is _much_ more important), but it's good to be
aware of the issue.

--
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