AJA FS1 - Manual (Page 37)

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29 FS1 Installation and Operation Manual — Cabling the System
The analog audio levels listed on the next page are defined in reference to 0 dBFS
(where FS = full scale), which is the maximum level that can be represented digitally.
Note: test criteria mentioned here involves a 1kHz sine wave.
FS1 Professional Audio Level Settings
FS1 Consumer Audio Level Setting
How Do Audio Levels Settings Relate to Nominal Levels?
Most users refer to audio levels at the Standard Operating Level for the U.S. and
Alignment Level for the EU—a level not at maximum level, but rather at some lower
point to allow “headroom” for audio to become louder without clipping.
In the U.S. most users use +4 dBu as their Standard Operating Level. This
corresponds to -20dBFS in the digital domain (20 dB of headroom, per SMPTE 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.
FS1 Audio Setting Meaning
+24 dBu analog = 0 dBFS SMPTE standard With digital audio at maximum possible level
(before clipping), the expected analog audio
input level is +24 dBu, and the output will be
scaled to this level.
+18 dBu analog = 0 dBFS EBU standard With digital audio at maximum possible level
(before clipping), the expected analog audio
input level is +18 dBu, and the output will be
scaled to this level.
+15 dBu analog = 0 dBFS With digital audio at maximum possible level
(before clipping), the expected analog audio
input level is +15 dBu, and the output will be
scaled to this level.
FS1 Audio Setting Meaning
+12 dBu analog = 0 dBFS. With digital audio at maximum level (before
clipping), the analog audio input level will be
+12 dBu, and the output will be scaled to
this level.
These levels are provided for consumer
equipment that outputs audio at levels lower
than the professional levels.
Note: In the consumer audio world, units are
often given in terms of dBV, so +12.2dBu is
equivalent to +10dBV. The standard
operating level then corresponds to -10dBV
(-7.8dBu). The "+12dBu" FS1 setting
provides consumer audio levels with
headroom.