Device sync follow up

[Watchmaker]

Last week members of the forum were kind enough to assist my thinking about how to structure word clock syncing across several devices https://www.soundonsound.com/forum/view ... 3&p=954413.

I've since done some reading here on SOS (for example https://www.soundonsound.com/techniques ... ster-clock ) and elsewhere. As I do not ever do video, I don't want to invest in another piece of gear if I can solve the configuration issue else-wise. It'd be interesting to know the qualitative differences in external clock latching for different interfaces/devices so one could make an informed decision about master/slave relationships. (hint)

I did a fair bit of brute force diagnostics on my system, swapping out instruments, using different inputs on the same device, using different input devices entirely, running through the amp DI, running the instrument direct to Hi-Z inputs, running the instrument to a DI and a mic in. All resulted in essentially the same waveform deformation shown in the other thread, only for the bass guitar signal, in a live recording session of 11 audio tracks.

Being mostly at a loss, I'm starting from the assumption my clocking is misaligned somewhere as changes to the signal chain from instrument to any preamp doesn't change the recorded outcome. Below are two scenarios I believe may provide satisfactory solutions. I would be deeply grateful for any input regarding these ideas. eg which is most likely to be stable and whether one presents more pitfalls than the other. Is there a different way to think about this?

The only other thing I can think of is somehow the bass track in Logic Pro has some hidden setting set somewhere or the template I use is corrupted but these thoughts seem irrelevant to the case.

Thanks as always. For clarification, the Focusrite and Apollo are combined in Core Audio as an Aggregate device and both units have input extensions feeding audio over ADAT. Under the ADAT sync scenario 1, I would enable drift correction on the Apollo to force it to sync to the Focusrite since both would use internal clocking to their respective ADAT slaves. Under the BNC Word clock scenario 2, I would not use drift correction on either device as the Apollo is sync'd via word clock. Please advise if this is not correct. Is there a technical preference for BNC WC over ADAT as a sync protocol, vice-versa or doesn't matter?

[Hugh Robjohns]

I did a fair bit of brute force diagnostics on my system, swapping out instruments, using different inputs on the same device, using different input devices entirely, running through the amp DI, running the instrument direct to Hi-Z inputs, running the instrument to a DI and a mic in. All resulted in essentially the same waveform deformation shown in the other thread, only for the bass guitar signal, in a live recording session of 11 audio tracks.

Would that not seem to imply the bass guitar itself is the problem?

Being mostly at a loss, I'm starting from the assumption my clocking is misaligned somewhere as changes to the signal chain from instrument to any preamp doesn't change the recorded outcome.

If it was a clocking issue it would affect everything recorded through the same interface/converter as the bass. And since ce that doesn't seem to be the case I don't see how it can be a clocking issue.

It has to be something in the bass signal path, but since you've apparently changed out everything there, that cant be the problem either.

The only other thing I can think of is somehow the bass track in Logic Pro has some hidden setting set somewhere or the template I use is corrupted but these thoughts seem irrelevant to the case.

I certainly wouldn't rule out a template or settings issue in Logic at this stage...

I'd suggest going back to basics and listen to the analogue bass sound you're feeding into the converter/interface. Is it clean? If you have access to a scope or an independent system (perhaps a DAW on a laptop) can that see/record a clean bass signal?

[Watchmaker]

Thanks Hugh, I will and report back. the issue occurred on two different basses.

There is one additional item that may be related although I can't see how. Whenever I first open Logic Pro, I get an error message saying "Error in Core MIDI: 1" and no MIDI is received from any input even though it registers in Audio MIDI Setup . I did much troubleshooting on that with zero result. I did learn that this occurs only the first time I open the program so my work around has been to close and reopen following which I get normal behavior. This began after installing Native Instruments.

I have tried all the textbook stuff, uninstalling NI (a very unpleasant tasks and shame on every developer who fails to provide a decent uninstaller), reinstalling the OS. I could do a clean install but that would really piss me off! lol

What do you think? Is a connection between the two issues remotely possible?

[Hugh Robjohns]

I dont see how midi would affect it.

The difficulty with solving this kind of problem remotely is not being in possession of all the pertinent details or being able to see the whole picture.

As I said, the first thing to do is confirm whether the signal coming out of the bass signal path is clean at the point it enters the converter/interface?

If it isn't, you'll need to work through that analogue signal path, stage by stage, to find where it is being corrupted.

If it is clean at the input to the interface/converter, then do you get the same problem if you use different channels of the same converter/interface?

Do you get the same problem if you connect a different source to that converter/interface input?

What if you route the bass input hardware channel to a different (or new) track in Logic?

What if you disable the aggregation and run a single interface (operating on its internal clock) into the computer?

[RichardT]

Although I’m not thinking that the core midi problem is necessarily related, it made me wonder whether something is going wrong with the ‘audio’ components of core audio (possibly indirectly related to having an aggregate device).

When you’re having problems, you could try resetting core audio and see if that helps (you probably know already that core midi is a component of core audio).

[Watchmaker]

Thanks Richard. That's my line of thinking, but for the life of me I can't see how! It's hard for me to even consider Core Audio being related to this. I've run these two boxes as an aggregate devices for years without issue.

Once I get back to the cave I'll follow Hugh's recommendations after I try a different DAW. I'm also going to rewire the devices so the daughter's sync via ADAT instead of BNC and go from there. I do appreciate the help.

[James Perrett]

It may be worth saying that you can't sync the ASP880 via ADAT unless you use it as the master clock. It only accepts external sync via word clock.

[RichardT]

Thanks Richard. That's my line of thinking, but for the life of me I can't see how! It's hard for me to even consider Core Audio being related to this. I've run these two boxes as an aggregate devices for years without issue.

Once I get back to the cave I'll follow Hugh's recommendations after I try a different DAW. I'm also going to rewire the devices so the daughter's sync via ADAT instead of BNC and go from there. I do appreciate the help.

If it were me, I would write down an explicit checklist of all the possible sources of error and validate that I had eliminated them one by one. It's a complicated problem!

[Watchmaker]

It may be worth saying that you can't sync the ASP880 via ADAT unless you use it as the master clock. It only accepts external sync via word clock.

Thanks James!

I rewired the clocking so that the Focusrite and the Apollo are both set to their own internal clocks. The Focusrite drives the Pulse via ADAT and the Apollo drives the ASP880 via WC (terminated) so two distinct legs.

The FR and Apollo are set up as an aggregate device with drift correction enabled on the Apollo as it's been for yonks. Works fine.

I'm going with the conclusion that using the Pulse as Master and daisy chaining the ASP880 from the Focusrite WC out was the problem.

Thanks all for the assist. Invaluable! I learned much.

Now I have many question re: how clocks are implemented in circuitry. I don't suppose there are many mid level technical resources on clocking. It's an area I haven't spent much time on outside of the basics of AD/DA theory and this experience has piqued my interest.

[RichardT]

Great news!

Here’s a guide to clocking from DCS

https://dcsaudio.zendesk.com/hc/en-gb/a ... 9109330844

[Watchmaker]

yea. nice summary doc thank you. I'm ready to go deeper into circuit design a bit. I've always sort of assumed the ADC sits across all inputs and the DAC across all outputs. I hadn't realized the clock was regulating power as well.

I have a military electronics background in RADAR and radio and began studies of digital circuit theory and design waaaaayyyy back in the mid 80's before I decided to be a touring musician instead. (that turned out to be a poor decision - literally!)

It's been a long time since I accessed that memory and things were still going through birthing pains as far as ADDAC is concerned. Maybe I should take a class somewhere.