If you are just using the Saffire 56 for transferring the S/PDIF and ADAT data streams to your computer, it does not need external sync - you lock the Saffire to either of the incoming digital inputs. However, this pre-supposes that the S/PDIF and ADAT data are themselves synchronised together, so it's a good plan to take the BNC wordclock out of the Mytek ADC and feed it into the external wordclock input of the Octopre. Use 75 Ohm BNC cable, T-piece and terminator. Note that instead of copper cable via an RCA connector, you could use an optical cable between the Mytek and the Saffire, with optical input 2 switched to S/PDIF. By doing this you would reduce the chance of ground current noise getting into the audio.

If you need to use some of the analog inputs of the Saffire 56 as well, you should consider routing the Mytek wordclock to both the Octopre and the Saffire so that it gets the best-quality clock. Use a second 75 Ohm BNC cable and T-piece to extend the daisy-chain. The chaining order is unimportant.

Your example is a good one in that it illustrates the difference between a clock supplied for data locking purposes (first case) and a clock supplied for conversion and locking (second case). A clock regenerated from an incoming ADAT or S/PDIF stream is perfectly sufficient to keep the digital data flow in lock, but you can usually do better if you need it for accurately timed (low-jitter) conversion sampling.

Boswell, post: 407912 wrote: Note that instead of copper cable via an RCA connector, you could use an optical cable between the Mytek and the Saffire, with optical input 2 switched to S/PDIF. By doing this you would reduce the chance of ground current noise getting into the audio

Thanks for your answer Boswell,

About using the second Toslink for the mytek... I will consider the idea. But, by doing so I would limit myself from going higher than 48khz, Right ? Both adat inputs are needed on the saffire from the octopre to run at 88.2khz.

How likely is it possible to have ground noise on a digital signal by using a spdif RCA connectors ? Forgive me for being so newb on digital transfers, but aren't digital a bunch of one and zeros being transfered that should not be affected by ground noises ??

Thanks again

Ok I read a bit found this :

NOTE: The OctoPre MkII Dynamic's word clock input is termintated (75Ω). Therefore the OctoPre MkII Dynamic should be the last device in a chain of word clock connected digital devices.

The last question I have is, can the Mytek clock output go to the input of the saffire and the output of the saffire to the octopre or do I need a T on the input of the saffire to continu the chain to the octopre.. ??

Yes, that's true about the 48KHz limit. Once you have got it set up and working, it might be worth doing a quick test (at 44.1/48KHz) with copper and then with optical S/PDIF connection to see if there is any difference in the baseline noise. The test is not completely straightforward, since you have to look at what the baseline is doing underneath a large signal rather than with no signal. A reasonably pure sinewave is what is usually employed in this type of test with a power spectral analysis display.

The point about the optical connection is not that noise could affect the digital signal transfer, but that it stops computer/interface ground noise getting from the computer into the analog front ends and hence affecting the signal before it is digitised. It's only a small point, and I think you will be very happy with the audio quality you get from a Focusrite ISA feeding a Mytek however it's connected at the back end.

Yes, you can daisy-chain the BNC from the Mytek to the Saffire and on to the Octopre. It's not input and output on the Saffire - use a BNC T-piece on the input connector.

I'll make the tests.. Many thanks !

A little follow up ; Using the ISA two with the Mytek instead of going in a line in of the liquid saffire 56 makes a lot of difference as expected. Actually the sound is much more different then I thought..

As for the world clock, I should have the T that I miss for completing the connection today..

The results : spdif rca sync is a pain.. always dropping.. (tried it just for fun)

I have yet to record a full band .. but it seem solid.. I'm rediscovering the ISA preamps.. This weekend I'll make more tests..
For those who don't believe in 1000$ 2 channel converter and world clock unit.. you'd be surprised !!! thumb

Thanks for the good suggestions !