Saffire Pro 14, Pro 24, Pro 24 DSP, Pro 26
Scarlett 8i6, 18i6
Scarlett 6i6, 18i8, 18i8, 18i20 (1st and 2nd gen)
Clarett 4Pre, 8Pre (USB and Thunderbolt)
The S/PDIF RCA connection on the back of your Focusrite interface is a connection that allows two channels of S/PDIF Format Uncompressed Digital Audio to be passed along a single unbalanced coaxial connection. This can be used to connect a device with a digital output or input to avoid unnecessary conversion from analogue to digital and vice versa.
To send audio to another external device
If you are sending audio from your Saffire or Scarlett to another device you should first connect the S/PDIF output of the interface to the S/PDIF input of the external device using a coaxial S/PDIF cable - such as a CD recorder.
You should then launch Saffire or Scarlett MixControl (for Saffire and 1st generation Scarlett interfaces), or Focusrite Control (for 2nd generation Scarlett and Clarett interfaces) in order to route audio to the S/PDIF outputs. To do this, select the desired S/PDIF output (pictured below) and choose what you wish to route to this output using the drop-down menu. Make sure that if the S/PDIF input is connected to the same external device it is muted to prevent unwanted feedback.
If you use an interface that uses Mix Control, you can decide which audio you wish to send to the S/PDIF output in the highlighted area.
If you use an interface that uses Focusrite Control, you can decide which audio you wish to send to the S/PDIF output in the highlighted area.
You should also select the 'Sync Source' to 'Internal' in Mix Control or Focusrite Control and refer to the user guide of the external device to set its sync source to external S/PDIF. This will ensure the external device receives digital clock from the Focusrite interface reducing the chance of experiencing clicks, pops or interrupts in the audio. You should also make sure the sample rate for both the Focusrite interface and the external device are the same.
To receive audio from another external device with a S/PDIF output
If you are receiving audio from an external device (such as a two-channel Guitar FX Processor or an external microphone pre-amp) you should first connect the S/PDIF output of the external device to the S/PDIF input of the Focusrite interface.
You should then launch Mix Control or Focusrite Control and set the sync source to S/PDIF (shown below). You should also refer to the user guide of your external device to make sure that it is set to its internal clock. Finally, make sure that the sample rate of the two devices are matching. The output from the external device should now appear as the S/PDIF Inputs within your DAW software. The input number will vary depending on which Focusrite interface you have and more information can be found in the user guide for your specific interface.
If you are using an interface that uses Mix Control, you can change the sync source use the drop-down menu. When the sync status is showing Locked, it means that the interface is ready to receive audio from the external device.
If you are using an interface that uses Focusrite Control, you can change the sync source use the drop-down menu. When the sync status is showing Locked, it means that the interface is ready to receive audio from the external device.
Which cable should I use?
For more information regarding which cable to use for a coaxial S/PDIF connection, please see this article.