Universal Audio Apollo x4 Hardware Manual page 30

S/PDIF Optical I/O
When set to S/PDIF, an optical port routes two channels of digital I/O with resolutions up
to 24-bit at 96 kHz.
Sample rate conversion can be performed on the S/PDIF input. This setting is enabled
within the S/PDIF channel's input strip in the Console application. When the sample rate
of the incoming S/PDIF signal does not match the sample rate specified in the Console
application, the S/PDIF signal is converted to match Apollo x4's sample rate. If Apollo x4
is set to use external S/PDIF clock source, sample rate conversion is inactive.
Tip: The S/PDIF output can be configured to mirror the Monitor Outputs, for
routing the stereo monitor signals to the stereo S/PDIF input of other devices. This
feature is set with the DIGITAL MIRROR menu in the Hardware panel within the
Console Settings window.
(20) Thunderbolt 3 Port
Connect the Thunderbolt 3 cable (not included) from the host computer here. A
Thunderbolt 3 connection to the computer is required to use all Apollo x4 features and
UAD Powered Plug-Ins.
Note: With Mac computers only, Apollo x4 can be connected to Thunderbolt 1
and Thunderbolt 2 ports by using the Apple Thunderbolt 3 to Thunderbolt 2
Adapter in conjunction with a Thunderbolt 2 cable. With Windows PC computers,
connections to Thunderbolt 1 or Thunderbolt 2 ports on are not supported.
Apollo x4 Hardware Manual 30 Controls & Connectors