JBL LSR4328P Owner's Manual page 19

After changing the input source, the Active Input display on the rear panel will
indicate the current selection.
When monitoring digital (S/PDIF or AES/EBU) signal, the rear panel DIP switches
must be set correctly in order to determine which channel is being reproduced. For more
information, see page 23 in this manual.
If you select a digital input to which no signal is connected, no signal will be heard, and
the left-most meter segment will flash to indicate an error condition.
S/PDIF input selected (channel A)
S/PDIF input selected (channel B)
AES/EBU input selected (channel A)
AES/EBU input selected (channel B)
Reference - Front Panel
15