I bought a second hand Focusrite Octopre Platinum yesterday to get more inputs on my Fireface UC via ADAT. I'm new to ADAT and word clocks (always used the Fireface as 'standalone' device in my computer setup) and I've been reading the manual a few times to understand it.

Everything seems to be working correctly. I connected the Octopre via a Toslink cable to the Fireface UC. I immediately saw the ADAT light blinking, so I went into the Settings page. There I saw my Clock Source was still internal, causing the ADAT input status to toggle from lock to sync every second. I changed the Clock Source to Optical In, set the Octopre to 24/44 (my default recording setup) and voila: it synced. Did a few test recordings, it's working very well.

Now here's my question: as an enthusiastic user of the pitch/varispeed function I noticed it doesn't work in this setup (with Clock Source Optical In). The only way to get it working is setting the Clock Source to internal (and not use the Octopre I guess). Not that this is a big problem, but in the manual I read the line 'Bitclock PLL ensures perfect synchronisation even in varispeed operation' and I was wondeing if I'm doing something wrong or misunderstand the meaning of that line. Like I should feed the Octopre with a external word clock from the Fireface via BNC and set it to External sync, so the Fireface UC is always master?