The ISA One, 220, 428, 430, 430 MkII and 828 can be fitted with optional digital converter cards. If your unit has one of these cards fitted and you are connecting digitally to other equipment (via AES3, S/PDIF or ADAT) then the ISA unit must be in sync digitally with all other digital audio devices in the signal chain. The way you sync the devices together depends on how many devices are in the signal chain and which device you select as the Master clock.
There are two ways to configure an ISA in a digital audio system:
1. Clock Master
In this configuration the ISA generates the clock signal for all digital devices in the setup.
Connect the digital audio output of the ISA (ADAT, S/PDIF or AES3) to the corresponding digital input(s) on the receiving device and then set the receiving device to sync to its digital input. For example, to use the ADAT format, connect the optical ADAT output of the ISA unit's digital card to the optical ADAT input of your audio interface, then select the clock source for your audio interface to ADAT.
If there are additional digital devices in the rig then you should connect the BNC word clock output on the ISA to the word clock input of those devices, then set those devices to receive their sync over wordclock.
In this configuration you need to connect a BNC wordclock cable to the wordclock input of the ISA so that it can sync to an external master clock. You will need to select 'Ext' as the sync setting on the front of the ISA, or 'Ext S/C' if the clock signal is 256x 'Superclock' (NOTE: the ISAs will not generate Superclock, only receive it).
The signal seen at the ISA's 'wordclock in' connector will be regenerated at its 'wordclock out' connector. This can be useful in more complex setups where you have multiple digital audio devices as the clock can be passed through (daisy-chained) to other devices from the ISA.
If you have a very complex setup, it may be beneficial to utilize a third-party wordclock generator to provide clock to all of your digital devices.
NOTE: it is important to set the sample rate and bit depth settings on the front of the ISA to the same settings for the rest of your system, even if the ISA is slaving to a wordclock signal.