Some Focusrite interfaces feature ADAT inputs and outputs. ADAT is a digital format carried using optical (sometimes referred to as "TOSLink") cables.
The number of channels transferred between two devices over a single ADAT cable depends on the sample rate being used, please see the table below:
|Sample Rate(s)||ADAT Channel Count|
|44.1kHz and 48kHz||8 Channels|
|88kHz and 96kHz||4 Channels|
|176.4kHz and 192kHz||2 Channels|
An audio signal transmitted via ADAT can only travel in one direction down a single cable. If you want to send audio signals in two directions using ADAT you will need two cables and both devices need ADAT In and Out ports.