Word clock master

Hello all, I scored a cheap appogee rosetta 800 and am hoping to incorporate it into my setup. I’ve spoken to a couple people who said that for the rosetta to really shine i’ll need to make sure that i use it as word clock master. I’ll likely be interfacing the rosetta to my laptop with a minidsp usbstreamer b or some other usb interface with ADAT optical inputs/outputs. My question is this, how does jack ardour handle word clock? if i set the rosetta as master on it’s panel will ardour recognize that? I’m completely inexperienced with word clock so please excuse the question.

I’m on fedora 31 running ardour 5 and harrison mixbus 6.

thanks a bunch

Jeremy Boyd

I’m trying to figure out the nuances of the MIDI stuff myself. I think you just have to make sure that the hardware is inputting to Ardour’s MIDI clock. If you open the MIDI Connections window (Shift+Alt+M), go to the tab for “Hardware” on the vertical axis (Sources) and then to the “Ardour MIsc” tab on the horizontal axis (Destinations). Connect the Input from the hardware to “MIDI clock in”. I think that should do it.

Neither Ardour nor JACK cares. Word clock is used to synchronize device on hardware level.

An analogy: If you read the time on your wristwatch, you don’t have to know how that timekeeping works under the hood. You just take it for granted. JACK does the same.

If you use two soundcards, you’ll want them to be in sync. This is like synchronizing two clocks.

When you have a soundcards running at, say, 44100 samples/second. It is never exactly 44000 samples/sec. It may be 44100.001. Now if you have a second soundcard it may sample at 44099.997 samples/seconds. Over time they will drift apart.

The solution is to send “clock pulses” from one device (the master) to another. So the devices can synchronize their sample-clock and update in lock-step. This prevents drift.

A 2nd consideration is to pick the “master clock”:
Some cheap devices have a poor internal clock, that jitters, or is always a bit to slow/fast depending on temperature, power-supply or whatnot. In that case you want to slave this device to a steady clocks-source from a reliable master-clock.

I don’t know any of the devices you mention, but apparently the persons you spoke to suggest to use the Rosetta 800 as master, and have other device use the clock from it.

After that you start jackd using the rosetta as main device, and then add the other using alsa_in, alsa_out or zita-ajbridge’s zita-a2j, zita-j2a.

If you are using the miniDSP USB streamer then open whatever control application is appropriate for your operating system and make sure to set the clock source to ADAT clock and not internal clock. Make sure to make the complementary setting on the Apogee, set the clock to internal and not to external ADAT clock.

If you only have the one interface then that is all you need to set.

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Thanks for the valuable info. The USB - ADAT interface manual shows that you can select an internal clock or get the clock from the ADAT input, which i would want too do. The question is now whether that setting will be accessible from alsa mixer or my audio settings panel since i doubt they made their software available on linux…

It should be, I believe that interface is USB class compliant, so it should expose the clock source setting.

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