using two different Digilink interfaces on one HDX card -- what am I doing wrong?

[zachxweeks]

TL;DR: trying to run two different pieces of Digilink hardware (Burl Mothership and Digi 192) on the same HDX card and running into issues at sample rates above 48 kHz. I


Running an HDX PCIe card on Mac OS (Pro Tools 2023.12) with a Burl Mothership over one of the two available Digilink ports. The Burl is configured for 24 ins and 32 outs and we have been running this rig for many many years with no issues.



The Burl connects to the HDX using a "BMB1 Digilink" card for 64 channels of I/O, but we are only using 32 hence one Digilink cable. It has two Digilink ports, two BNCs for clock out, and one BNC for clock in.





The Burl BMB1 is set to receive sample rate / clock from the DAW. The Burl is configured as the "master" unit in Pro Tools hardware setup.





I am trying to add an older silver/blue Digi 192 for some additional I/O. I have one (manufactured in 2010) outfitted with the digital I/O and then analog in and analog out cards. That is connected to the second Digilink port on the HDX.



Breakdown here:

• I have TWO BNC cables coming out of the Burl and going into the Digi 192's "loop sync" jacks.
  • I did not test to see how the Digi 192 worked with BNCs connected to the "external word clock" versus the "loop sync" jacks.
    
    
  • I also am not sure if connecting anything to/from these "loop sync" jacks is even necessary considering the Burl is receiving clock from the DAW, or if I have this configured correctly.
    
    
• At 44.1 kHz and 48 kHz, I am able to get both the Burl and the Digi 192 working together just fine on all channels. Plug and play, no setup in Pro Tools HW window or anything.
  • "Loop sync" indicator on the 192 is on. Loopback on the 192 is perfect and the noise floor is actually lower than the Burl
  • Running a click track recording loopback on both units simulataneously (24 I/O of the Burl plus the 8 I/O of the Digi 192) is great with no sample offset between the units (the Burl is 4 samples late, but this always happens regardless of the Digi 192 being connected or not)

However, at any sample rate above 48 kHz, things get wonky. This is with PT automatically switching sample rates rather than manually setting the sample rate on the Burl or elsewhere.

• The sample rate indicator on each unit shows the correct sample rate (e.g. 88.2 kHz or 96 kHz), but the 192's "Loop Sync" indicator flashes/blinks rather than a solid light.
• At 96 kHz, both interfaces work without any clocking noise BUT the latency is all screwed up. With PT buffer set to 128 samples, the Burl becomes 44 samples late and the Digi 192 appears to be 13 samples EARLY which I really don't understand at all.
• When recording loopback on the Digi 192 at 96 kHz, audio is distorted.
• Everything goes back to normal / works fine after switching back to a 44.1 kHz or 48 kHz session in PT (without any rebooting of computer or hardware)

I hooked up the 192 with the "loop sync" jacks because that is what someone told me to do. I did some research on the duc here, Gearspace, and elsewhere but can't find anyone running into the same issues I am. I was told that I don't need an Avid/Digi Sync unit because of the configuration, but I really don't know!

Thank you!

[Darryl Ramm]

Sounds like it is working as expected for clocking at least, since loop sync is base sample rate clock.

"what somebody told me to do" I am shocked that somebody does not know what they are talking about.

If things have different names, maybe don't connect 'em and connect the things with the same name.

Lots of ways to do this, but just use the 192 as the clock source and run it's WC out to the WC in on the Burl.

And yes a "better" DigiLink adapter would have Loop Sync.

As for latency, I have no idea if the Burl correctly emulates latency of the HD I/O or whatever it is emulating. Not all DigiLink boxes do, should be made clear in the doc, or ask Burl. If not you need to manually adjust for this in Pro Tools, all it does is assume a fixed input and output latency for the device based on what Avid device it thinks it is. Negative offsets are simply Pro Tools assuming and correcting for more latency than there is. Not sure why the 192 would be off, but fix other problems and test again, if still screwy maybe test the 192 alone. If still stuck describe exactly what you are doing (eg is this used for track inputs or H/W inserts etc. are you measuring analog or digital ports on the 192 etc.) and how exactly you are measuring latency.

Absolutely no need for a Sync HD or X box, that is completely irrelevant. You are not trying to frame lock video etc.

[zachxweeks]

Thanks @Darryl, all good tips. I should have also stated that I spent about 30 minutes experimenting with this total...


The 192 was rigged up as the second-in-line in terms of Digilink port, but I'll give it a shot running that as the clock source / master in HW setup and see what happens. Will report back eventually.

[zachxweeks]

just a heads up and hopefully helpful tip for anyone interested, got this working perfectly at all sample rate with no issues.



steps:

• running a short length, high quality RG-59 BNC cable with proper 75 ohm connectors from the "word clock out" of the Burl M80 into the "word clock in" of the Digi 192, with the Burl M80 set as the master clock in Pro Tools Hardware Setup
• the "Digital I/O" card in the Digi 192 rack was disconnected. Although this isn't being used on my end, turns out you *must* have the Digital I/O card in place for the unit to work. Only figured this out when I disassembled the unit to replace the noisy fan.

...and that's all it took! 8 channels of analog I/O working great alongside our 32-in / 24-out Burl rack.