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Probably basic clocking question
Old 6th February 2015
  #1
Probably basic clocking question

This is a tough one to search because different stuff comes up, but is one of those stupid questions that I probably should know. I think I figured it out somewhat through testing but I wanted to get confirmation.

Question: When I try to run 8 channels via lightpipe from a Digimax to an 896, "it don't work right."

Answer: When you try to send 8 channels of audio and word clock over the same cable (so using Digimax as clock), then the clock data takes up channels 1 & 2, and nudges everything to the right. So audio 1 & 2 shows up on DAW channels 3 & 4 etc..., and the audio from inputs 7 & 8 gets bumped off the edge and disappear.

Is that correct? I only think this because in my DAW it's exactly like I'm describing, but the weird thing is that the audio shows up properly on the 896 meters on channels 1-8.

Or does that make it a firewire limitation instead? (Since all 8 channels are making it over the toslink). Of course that doesn't make sense either since I know FW can carry over 16 channels of audio.

I don't have another toslink cable here to run the other way and test clocking from the 896, nor do I have a coaxial cable handy (damn you netflix) to try separate clocking. So what's the best way to get all my audio plus word clock synced up (bonus points if anyone knows what would be the best source to clock from).

REMEMBRANCE: I am running my FW400 cable to a thunderbolt adapter, would that have anything to do with anything?

Thanks!
Old 7th February 2015
  #2
Gear Nut
Adat will always send clock afaik, doesn't matter if you choose to use it or not. The only time I've ever seen it 'nudge channels' is in SMUX mode where 1+2=1, 3+4=2 etc.
Not sure which digimax, your using but if there are 2 outputs make sure you are using the main, and if you only have 1 cable plugged in make sure it's set to base sample rates.

After saying all that it sounds like a routing problem in your interface.
Old 7th February 2015
  #3
I always track at 44.1k. In the test I actually wound up on 32k by mistake and even that didn't get me 8 channels. When you say routing, what exactly do you mean? The only settings I have to play with are in the MOTU control panel, and those don't really get messed with - except for since this happened. The Digimax is the original LT which only does 32, 44.1, and 48k. 1 in, 1 out. Word clock and AES too. Are you saying that if I try sending clock a different way that it will also still go out via optical?

Maybe something's just broken...I think I'm going to get another toslink cable and try clocking from the MOTU, see if that changes anything. Beyond that, I dunno.
Old 7th February 2015
  #4
Lives for gear
 
Neenja's Avatar
 

The clock is embedded like with SPDIF and TOSLINK. The channels will be right where they are supposed to be.
Old 7th February 2015
  #5
Lives for gear
 

There's something wrong with the config of the 896 or of the Digimax. ADAT clocking doesn't work the way you think it does - the clock signal doesn't replace (or bump) any channels. At 44.1 or 48, ADAT only delivers 8 channels and they all carry digital audio. The clock signal is recovered from the digital audio signal itself - it isn't carried separately. As far as I'm aware, the only time that clock is carried separately is if you are using a proper word clock connection in which case you have a separate, dedicated word clock cable alongside your digital audio cables.
Old 8th February 2015
  #6
Huh ok thanks guys that sheds a lot of light on the situation (and on clocking in general). So basically there's something wrong - but probably nothing to do with ADAT but with the 896? I'm just guessing, since like I said the audio shows up properly on the MOTU's meters, but then gets into the computer wrong. It's kind of a weird manifestation though isn't it? The audio comes through fine on channels 3-8, it's just literally in the wrong spot.

I have another 896 that I haven't been using, I'm going to dust it off and see if the problem repeats itself with that box.
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