PRESONUS StudioLive CS18AI Owner's Manual page 51

5 Controlling StudioLive RM-series Mixers with the CS18AI
5.3 Processing Signals with the Fat Channel
dBu and dBFS
Mixes displays the output level of each of the 16 aux mixes or subgroups.
Main meters display the level of the Main Center/Mono, Left, and
Right outputs. These meters are scaled from -60 to +24 dBu.
Power User Tip: Because of the different full-scale reference between the
subgroups and the Main Output meters, you may notice a slight metering variation
when a single channel is patched to both a subgroup and the Main bus.
Selected Channel meters are dedicated to displaying information about the
currently selected channel. The meter on the far left of this section displays the pre-
fader input level for the selected channel. The two meters to the right of it display
the compressor and gate gain reduction applied to the selected channel. These
meters are only active when one of the input channels or an aux bus is selected.
The CS18AI meters the channels and the main and subgroup buses
using two different reference scales. The channel levels are measured in
dBFS and the output levels are measured in dBu. To understand how this
impacts the metering on your StudioLive system, you must be aware of
the difference between dBu and dBFS and how both are measured.
dB is an abbreviation for "decibel. " One decibel is equal to one-tenth of a Bel.
When a measurement is stated in dB, it is describing the ratio between two
levels: the level being measured and the level being referenced. Without
a reference point, the absolute dB value cannot be determined.
dBFS, or "decibels relative to full scale, " is used to measure amplitude levels in
digital systems that have a maximum peak level (the point at which the A/D
converter will clip). When measuring in dBFS, 0 dBFS cannot be exceeded. 0 dBFS
can equal +10 to +24 dBu, depending on the device's maximum peak level. For
StudioLive-series mixers, 0 dBFS equals +24 dBu in the main output meters.
dBu measures decibels relative to 0.775 volts with an open or unloaded
circuit. (The "u" in "dBu" stands for "unloaded. " ) While 0.775 volts may seem
rather arbitrary, it is the voltage level that delivers 1 mW in a 600Ω resistor,
which is the standard reference impedance in a telephone audio circuit.
(The Bel was named after telephone inventor Alexander Graham Bell.)
Because the StudioLive subgroup and main outputs are electrical, rather
than digital, it is more advantageous to meter them relative to voltage.
StudioLive CS18AI
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Owner's Manual
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