Input Meters; Volume Knob [Aka Big Knob]; Mono Button; Mute Button - Mackie big knob studio Owner's Manual

28. Input Meters

These meters show the signal level of the currently
selected stereo source(es).They are made up of two
columns of 16 LEDs with three colors to indicate
different ranges of signal level, sideways traffic light
style.
For best real-world results, try to keep your peaks
bouncing between the green and yellow LEDs, the colors
of our beloved hometown Seattle Supersonics [RIP].
The red LEDs indiate clipping. Clipping creates
undesirable distortion and should be avoided at all
costs. If the red LEDs illuminate frequently, turn the
gain/trim knobs down.
Remember, audio meters are just tools to help assure
you that your levels are "in the ballpark." You don't have
to stare at them (unless you want to).

29. Volume Knob [aka Big Knob]

Here we are with the money maker! The volume knob
– aka Big Knob – adjusts the volume of the selected
input source's signal going to the selected monitor
outputs. The volume knob ranges from OFF (∞)
to unity (MAX).
WARNING: Always turn the volume
knob all the way down before making
connections or trying something new.
Keep it down until all changes have been
made, then turn it up slowly. This saves your speakers –
and more importantly, your ears – from blowing.
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30. Mono Button

Mono is short for mononucleosis. It is an infection
that typically leads to a feeling of tiredness, although
one could also get headaches, a sore throat, swollen
glands and more. Thankfully, engaging the mono button
here does not produce the infection. Rather, the mono
here is short for monophonic.
Pressing the mono button combines the stereo
signal into a monophonic signal at the monitor outputs.
The left and right input signals are summed and the
mono signal is output at both the left and right outputs.
This allows you to check for phase problems in the
stereo signal when played over a monophonic system.
The button will illuminate white when engaged.

31. Mute Button

The mute button does just what it sounds like it
does. It turns off the signal at the monitor outputs by
"routing" it into oblivion. Engaging the mute button
(almost) provides the same result as turning the volume
knob all the way down. The button will illuminate white
when engaged.

32. Dim Button

Pressing this button turns down the signal going
to the monitor outputs by 20 dB. This allows you to
essentially "turn down" the speakers to converse without
affecting the speaker level. The button will illuminate
white when engaged.

33. PWR / USB / +48V LEDs

The PWR LED will illuminate green when the power
switch is turned on and the power cord is connected to
an active AC Mains supply. If it does not turn on, make
sure the power cord is correctly connected at both
ends, the local AC mains supply is active, and the power
switch is on.
The USB LED will illuminate green when the
computer is powered on and connected successfully and
securely (via USB) to the Big Knob. Different from the
power LED, the USB light informs you that the device is
"enumerated", and in a functional and happy state.
The +48V LED will illuminate green when the
phantom power switch is turned on. Phantom power
only affects mic channels 1-2.