A microphone normally needing 40dB gain would need 60dB gain and any peaks would drive both the
pre-amplifier and the A to D into clipping. Not good!
Depending on the reference level recommendations of the A to D manufacturer, the analogue levels on its
input should be typically around –18dBf. This will optimize both the signal to noise ratio and the
headroom of the analogue signal. A degree of variance, say –16dBf, is acceptable but higher levels will
begin to degrade the analogue performance with no improvement to the quality of the sound.
When using condenser microphones req48v, be sure to turn the volume control down before
pressing the 48v switch as applying this voltage may involve a switch on thump, especially if set to high
gains.
2. Compressor Details
The compressor can either be used on its own or in conjunction with the preamp equalizer
The drawing above shows the GTQC compressor section.
The five control potentiometers function as follows :-
NB
There is one further small detent at either end of the pot rotation.
Threshold (Grey knob)
:- A 17 detented potentiometer with a total range of 40dB, i.e from -10dBu to
+30dBu.
Ratio (Grey knob)
:- A 17 detented potentiometer covering a range of ratios from 1.5:1 to 10:1.
Attack (Blue knob)
:- A 17 detented potentiometer covering attack times from 500 microseconds to 5
milliseconds.
Release (Blue knob)
:- A 17 detented potentiometer covering release times from 100 milliseconds to 3
seconds.
Gain (Red knob)
:- A non-detented potentiometer covering gains from 0dB to +20dB. The silk screened
dB incremented scale is accurate and allows for fine level adjustments.
The eight illuminated switches are as follows :-
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