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Apollo x8 Hardware Manual Front Panel 16
(6 – 11) Preamp Options
This set of six switches control the preamp options for input channels 1 – 4. Press the
switches to toggle the setting. The current state of each preamp option is indicated by
the LED within each switch. Each switch function is detailed below.
(6) Input (Mic/Line)
This switch determines which rear panel input jack, either Mic (XLR) or Line (¼”), is
active for the channel. The switch has no effect if the channel’s Hi–Z input is connected
(the Hi-Z input must be disconnected to use the Mic/Line inputs).
Tip: Line inputs 1 – 4 can be set to bypass the preamp circuitry. See Line Input
Gain Bypass for additional details.
(7) Low Cut Filter
When enabled, the channel’s input signal passes through a low cut (high pass) filter. This
2nd-order coincident-pole filter has a cutoff frequency of 75 Hz with a slope of 12 dB
per octave.
The low cut filter affects the Mic, Line, and Hi-Z inputs. Low Cut is typically used to
eliminate rumble and other unwanted low frequencies from the input signal.
(8) Phantom Power (+48V)
When enabled, 48 volts of phantom power is supplied at the channel’s rear panel XLR
input. Most modern condenser microphones require 48V phantom power to operate. This
option can only be activated when the Mic/Line input switch (#6) is set to Mic.
Caution: To avoid potential equipment damage, disable +48V phantom power on
the channel before connecting or disconnecting its XLR input.
Depending on the current configuration of the hardware and software, there may be a
delay when changing the +48V state to minimize the clicks/pops that are inherent when
engaging phantom power. The +48V switch LED will blink rapidly during any delay.
(9) Pad
When enabled, the channel’s XLR input signal level is attenuated by 20 dB. Pad does
not effect the Line or Hi-Z inputs.
Pad can be used to reduce signal levels when overload distortion is present at low
preamp gain levels, such as when particularly sensitive microphones are used on loud
instruments, and/or if the A/D converter is clipping.
(10) Polarity
When enabled, the polarity (aka phase) of the input channel’s signal is inverted. Polarity
affects the Mic, Line, and Hi-Z inputs.
Tip: Polarity inversion can help reduce phase cancellations when more than one
microphone is used to record a single source.
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