User Manual

Apollo 8 Hardware Manual Rear Panel 23
(29) 75 Ohm Word Clock Termination Switch
This switch provides internal 75-ohm word clock input signal termination when required.
Word clock termination is active when the switch is engaged (depressed).
Apollo 8’s termination switch should only be engaged when Apollo 8 is set to sync to
external word clock and it is the last device at the receiving end of a word clock cable.
For example, if Apollo 8 is the last “slave” unit at the end of a clock chain (when Apollo
8’s word clock out port is not used), termination should be active.
(30) Word Clock I/O
Word Clock In
Apollo 8’s internal clock can be synchronized (slaved) to an external master word clock.
This is accomplished by setting Apollo 8’s clock source to Word Clock within the Console
application, connecting the external word clock’s BNC connector to Apollo 8’s word
clock input, and setting the external device to transmit word clock. If Apollo 8 is the last
device in the clock chain, the Termination switch (#10) should be engaged.
Important: Apollo 8’s sample rate must be manually set to match the incoming
clock’s sample rate.
Note: Apollo 8 can be synchronized to an external “1x” clock signal only. Super-
clock, overclocking, and subclocking are not supported.
Word Clock Out
This BNC connector transmits a standard (1x) word clock when Apollo 8 is set to use its
internal clock. The clock rate sent by this port matches the current system sample rate,
as specified within the Console application.
When Apollo 8 is set to use external word clock as its clock, Apollo 8 is a word clock
slave. If the incoming external word clock is within ±0.5% of a supported sample rate
(44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz, 192 kHz), Word Clock Out will mirror
Word Clock In with a slight phase delay (about 40ns).
Because Apollo 8’s word clock output is not a true mirror of the word clock input, word
clock out should not be used to daisy chain the word clock if Apollo 8 is in the middle
of the word clock chain. The correct method to connect Apollo 8 in the middle of a word
clock chain is to use a T-connector at Apollo 8’s word clock input and leave Apollo 8’s
word clock output unconnected (the Termination switch should not be engaged in this
scenario).