Allen&Heath GL4000 USER GUIDE - Manual (Page 17)

16
MONO INPUT
+48V - Feeds +48V to pins 2 and 3 of the input XLR for condenser
microphones which require phantom power.
Plug the microphone in before switching +48V on or off. Use +48V
only with balanced microphones and cables. No damage will occur
when +48V is switched to balanced non-phantom powered transformer
coupled dynamic microphones. However, always switch +48V off when
connecting line or unbalanced sources.
PHASE REVERSE - Reverses XLR input pins 2 and 3 to correct for
reverse wired cables or reversed phase signals. Can also be effective in
minimising acoustic feedback between the microphone and loudspeakers
in live sound mixing.
MIC/LINE (PAD) - Selects line input sensitivity when pressed, microphone
when released. Note that with the line jack unplugged the switch acts as
a 20dB pad for high output microphones or line input on XLR.
GAIN - Use this control with the MIC/LINE switch to adjust the channel
input sensitivity to match the connected source (-60 to +14dBu) to the
console operating level (0dBu). The gain should be set so that the channel
meter reads an average '0'.
LO-CUT FILTER - Reduces low frequency source noise such as
microphone proximity popping, stage noise and transport rumble. Can be
used to clean up sounds that do not have much bass content such as
vocals (around 150Hz), separate out the top end of a drum kit (400Hz),
reduce the handling noise of acoustic instruments, and so on. Select the
required cut off frequency by sweeping from fully anticlockwise (filter off)
to the maximum 400Hz. Setting the cutoff to 50Hz will have little effect on
most program material but will protect the low frequency speaker drivers.
The response drops by 12dB per octave below the cut off frequency.
EQUALISER - This provides separate, simultaneous control of 4
frequency bands. Each band may be boosted or cut by up to +/- 15dB
centred on the selected frequency which may be swept across a wide
range. Use the equaliser to correct for tonal deficiencies in the source
such as acoustic resonances or poor microphone response (corrective
EQ), or to change the tonal balance, for example to brighten up a guitar
so it cuts through the mix (effective EQ). You may need to adjust the input
GAIN control when using excessive amounts of EQ to compensate for the
change in overall signal level.
HF and LF affect the high (treble) and low (bass) frequencies respectively.
These have a shelving response which means that all frequencies beyond
the selected frequency are affected.
MF1 and MF2 affect the upper and lower mid frequencies respectively.
These have a peak/dip (bell shaped) response which means that the
maximum boost or cut occurs at the selected (center) frequency. The
MF1 and MF2 bands overlap for additional cut or boost when required or
to provide a tailored frequency response to suit any application. The
sharpness of the curve is selected using the Q switch to a Q of either 1
(wide band) or 2.4 (narrow band). Use wide band when you want to add
presence or warmth to the sound. Use narrow band to control problem
frequencies for example when notching out acoustic resonances.
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