How does clock sync work with simultaneous S/PDIF in and out?

[fredrick]

I'm considering purchasing the UltraLite-mk5. Its manual states the following with regard to the correct setting for S/PDIF clock syncing:

Clock Source setting = S/PDIF (when transferring from the other device to the UltraLite-mk5)
Clock Source setting = Internal (when transferring from the UltraLite-mk5 to the other device)

OK, but what about when both S/PDIF inputs and S/PDIF outputs are being used simultaneously? If I use Clock Source = S/PDIF, will the S/PDIF output inherit the input sources clock? If so, will I lose the S/PDIF output if the S/PDIF input source is shut down?

Also, there are potentially two S/PDIF inputs on the device (coax and TOSLINK), so with Clock Source = S/PDIF, what determines which of these two inputs is used as the clock source?

I'm very confused as to how S/PDIF clock sync is handled when more than one S/PDIF device is attached to the UltraLite-mk5. For the record, none of my S/PDIF devices have dedicated word clock connectors.

[HCMarkus]

Optical or Coax, SPDIF will support transmission of clock in both directions. As such, if an external device has both SPDIF In and Out ports and both are connected to your interface, that external device can work as either a Clock Master or Slave. If connecting ONLY the external device's SPIDIF In or Out to your interface, then the choices are limited as per the text quoted from the Ultralite Mk5 manual: an external device that is connected only by its SPDIF In port must necessarily be a Clock Slave. If connected only by its SPDIF Out port, the device must be a Clock Master.

As you know, only one device, your interface or an external device, can be the Clock Master. This is not an issue as long as there is no more than one device connected by only its Digital Output.

I have a fairly typical system with three devices connected digitally: My MOTU Interface, a PreSonus external expander that provides eight channels of analog I/O via optical I/O, and a Lexicon reverb with Coax SPDIF I/O. The external devices are digitally connected both to and from the interface. As such, any single device could serve as the Clock Master. The Master device must run from it's internal Clock. The other two devices must be set to Receive External Clock to Slave to the Master Clock.

In my case, my interface runs from its Internal Clock. There is a setting in the interface that allows this. (The Ultralite has a similar setting option, and the clock source is displayed on its front panel.) My PreSonus receives the interface's clock via a Word Clock BNC connection, but it could receive that same Clock from its Optical In Port. The Lexicon receives clock from its SPDIF In Port. Both the PreSonus and Lexicon are set to receive external clock.

OK, but what about when both S/PDIF inputs and S/PDIF outputs are being used simultaneously? If I use Clock Source = S/PDIF, will the S/PDIF output inherit the input sources clock? If so, will I lose the S/PDIF output if the S/PDIF input source is shut down??

You can certainly connect two external devices simultaneously using both the Optical and Coax ports and designate either Optical In or Coax In as Clock Master. Clock signal fed to the Ultralite via either of its Digital In ports (Optical or Coax) will be passed through to the other format Digital Out Port. For clarity: Clock received at Coax In on the Ultralite will be expressed at the Optical Out port when the Ultralite is set to receive clock from its Coax In and vice-versa. Of course, whatever device is the Clock Master must be powered on and connected for the system to function.

The phrasing of your question has me wondering whether you hope to connect two different external devices to the Coax SPDIF Ports simultaneously; one device to the Coax In and a second to the Coax Out. I am uncertain whether the the Coax SPDIF Out port will mirror the clock received on its corresponding Coax SPDIF In port. My guess is it would not, but if this is your desire, a call to MOTU should get you an answer, (or perhaps someone else will come in with the info.)

[mikehalloran]

This is one of those times when searching the pdf manual is helpful. Pull it up in a browser, Control f or Command f, use clock as your search term (44 mentions) and scroll through all the pages where it appears using the arrow keys. One or more pages should tell you what you need to know — or help narrow down the question.

https://cdn-data.motu.com/manuals/usb-c ... _Guide.pdf

[fredrick]

The phrasing of your question has me wondering whether you hope to connect two different external devices to the Coax SPDIF Ports simultaneously; one device to the Coax In and a second to the Coax Out.

Thanks for your detailed response. What I'm hoping to do is the following:



The Source's S/PDIF Out will connect to Ultralite's* S/PDIF In, then the Ultralite's S/PDIF Out connects to a Bluetooth transmitter's S/PDIF In. From what you said in your second-to-last paragraph, it sounds like this will be fine. As long as the Ultralite is configured to use S/PDIF as its clock source (instead of internal), it will inherit the Source device's clock and pass that out to the transmitter also, resulting in all three devices being synchronized. The Ultralite and transmitter will be slaves to the source. To be clear, the source and transmitter are consumer oriented devices with single S/PDIF connectors and no configurable clock source.

*looks like it's going to be an Ultralite-AVB now, as I have discovered that the Mk5 does not feature the full routing matrix.

My second question about the two inputs was more of a hypothetical case, but that's all academic now that I'll have to go with the Ultralite-AVB which only has one S/PDIF In and one S/PDIF Out.