Applies to: 

• Scarlett 18i20 (4th Gen)
• Clarett 8PreX
• Liquid Saffire 56 (LS 56)

When connecting external preamps via ADAT, the biggest consideration is how all the devices are synced together. All digital devices in a signal chain must be synced to a common clock source to pass audio without any clicks, pops, or glitches. Larger and more complicated digital systems often feature a separate Lead clock; this is not usually necessary in a smaller system. The most common ways to sync two external preamps via ADAT without an external Lead clock are outlined below.

1: Syncing via Word Clock – audio interface as Leader

In this scenario, your audio interface (e.g. Scarlett 18i20 4th Gen) is synced to its internal clock and is the clock Leader. The two external preamp units (e.g. two Octopre) are synced to the interface via Word Clock and are the clock Followers.

2: Syncing via ADAT – audio interface as Leader

This setup is very similar to the one above, although the Word Clock connections have been replaced by extra ADAT cables going from the ADAT (optical) outputs of your audio interface (e.g. Scarlett 18i20 4th Gen) to the ADAT (optical) inputs of the external preamp units (e.g Octopres). The external preamp units (clock Followers) are then synced to the ADAT clock signal embedded within the ADAT connection coming from the audio interface (clock Leader).

3: Preamp units without ADAT inputs or Word Clock outputs – audio interface as Follower

When trying to sync two preamp units that don't feature ADAT inputs or Word Clock outputs, you should set one of the preamp units as the clock Leader. It is then possible to sync your audio interface (e.g. Scarlett 18i20 4th Gen) to the incoming ADAT connection from this unit, and then sync the second preamp to the audio interface via Word Clock. The audio interface can be synced to either of its two ADAT input ports, so it is important to ensure that the correct one is selected in its control software (i.e. Focusrite Control 2/Focusrite Control/Saffire Mix Control).