audio interface clock/sync issues (hardware)

Question

I have two FirePower FC610 interfaces. One is used exclusively by Kyma/Pacarana (connected to Mac using Sonnet firewire hub shared by Pacarana), the other exclusively by software running on my studio Mac, (connected to Thunderbolt on the Mac). The interfaces are connected to each other via optical cables -- both in and out. The interfaces both have a steady glowing light indicating that they both believe optical connections are working. I know have successfully used them with audio going *from* Kyma/Pacarana *to* software in my Mac. This may well be the first time I have tried to have both devices using optical ins and outs simultaneously in a sound-quality critical environment. I am getting glitches that sound like a clock/sync problem and am having trouble figuring out the best combination of settings to use. (Perhaps it's not possible without a master clock?) 

Kyma has 3 choices: Internal, SPDIF Input, and Syt match (I have no idea what this last one does other than cause "Silent Device" to show up for Audio Input and Audio Output).

Mac audio software has four choices: Internal, Device Internal Clock, SPDIF Input. and Mac.

Any suggestions as to the best choice of setting to use?

Comments

Make sure the fc610's are not cheating on your Pacarana! i.e. how do you make sure the computer and Pacarana are not trying to share the same interface? Maybe you could try with 2 computers and see if it works? If not, then the fault is in a poor clock of the fc610??

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I don't think that confusion/conflict on which device is using what interface. I have occasional experience with that ... and this is not that problem. I am wondering about the quality of the clocks in the two FC610s.

Answer 1

For the Mac, try: Device Internal

For the Kyma side: SPDIF

Comments

Thanks!

Yesterday, I altered my plan of attack just a bit. I disconnected the optical cable for digital input into Kyma and worked on passages where audio into Kyma was analog and audio output of Kyma was recorded into DP. Kyma setting was internal; DP setting was SPDIF Input. That seemed to work reasonably well. Does that make sense?

I do need to get back to using the set-up with digital audio going both ways between the two interfaces. So I'll give your suggestion a try today. Thanks again!

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I take back what I said at the end of the first paragraph about it working reasonable well. Close listening to soloed tracks reveals intermittent clicks. So I'll have to redo most everything from yesterday.  :-(

Answer 2

Here's a short guide to avoid Jitter (those clicks you mentioned): Digital connections should share the same MasterClock. This can be either the interface connected to Kyma or the interface connected to your computer. One should be set to internal, the other one to the according connection, for example SPDIF or Optical. Also they should share the same samplerate, otherwise the syncing doesn't work. If there are more than 2 interfaces involved, the same rules apply, only one can be the Master. That's actually it, let me know how it goes ;)

Comments

Yeah.... I'm familiar with the idea of only one master clock since the days of locking analog multi-track audio, video, and film to audio SMPTE timecode. I tracked down one source my glitch and click problems ... buried deep in a granular synthesis sound patch I think a random number generator was occasionally causing an audio peak. But even after fixing that ,I still can't use the workflow I was hoping for when I purchased these two interfaces. I think may have another more serious hardware problem. I'm just using the interfaces separately and manually passing files back and forth. Tedious... but at least so far, the audio is clean and glitch free.

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I would suggest that you try to get the setup to work with analogue connection? With short cables there shouldn't be any quality issues.