Re: Multi Delta 1010 sync

[Doug McLain <doug@nostar.net>]

The only similarity between the 1010 and the 1010lt is the ice1712 chip 
itself.  The 1010LT doesnt use the 74HC4046, nor does it use the 
8404/8413 combo for spdif.  Until tonight, thats about as far as I would 
have been able to go with this conversation, but I finally hit paydirt 
with the spdif problems on the 1010lt. I posted a patch to bug 1806 
thats fixes spdif functionality, so that we 1010lt users can finally run 
2 cards together.  Now we can get some real world reports on 1010lt's 
running in tandem.  If the 96Khz issue exists for the 1010lt as well, it 
wont be a concern for me at all, since I consider anything over 48Khz a 
waste of space.  I did some testing tonight, and things are looking great!

John Rigg wrote:
> After some reverse engineering I've found out why I was having trouble
> syncing my two Delta 1010s at high sample rates using the word clock inputs.
> 
> The Delta 1010 uses a 74HC4046 phase-locked loop (PLL) to lock onto the word
> clock input signal. This is used in a feedback loop with a /256 counter to
> produce a frequency that's multiplied by 256x at the output of the PLL
> oscillator. With a 48kHz input this gives a PLL frequency of 12.288MHz.
> 
> According to the 74HC4046 data sheet, the maximum frequency it can
> work at is 13MHz. In other words, even a 48kHz clock is close to the
> specified limit, so forget about higher frequencies. (I didn't discover
> this until after I'd built a 96kHz word clock :-(. )
> 
> The S/PDIF receiver OTOH uses its own internal PLL which works with 96kHz
> sample rate. However,I couldn't sync reliably using the S/PDIF in/outs with
> one card as master and the other as slave. At 96kHz jackd would die at random
> times with a floating point exception, so often it was unusable.
> At 48kHz this would still happen, but not often (every couple of hours).
> I'm guessing that this is due to a phase difference between master and
> slave clocks.
> 
> My conclusion is that the only way to sync these cards reliably
> at all frequencies is to clock them both from an external S/PDIF device,
> and to make sure both cards are receiving the clock signal directly from the
> master device (ie. not going through the S/PDIF circuitry of the first card on
> the way to the second card).
> 
> John


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