AJA FS1 Version 2.2.0.47 - Manual (Page 42)

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RP-155), so the +24 dBu setting on the FS1 provides proper headroom levels for
digital and analog audio.
Most users in the EU use 0dBu as their Alignment Level. This corresponds to
-18dBFS in the digital domain (18 dB of headroom per EBU R68).
Correspondingly, the +18dBu setting on the FS1 provides for this relationship.
Alternatively, the FS1 +15 dBu setting provides safe headroom levels corresponding
to some German professional audio equipment.