Allen&Heath MIXWIZARD3 20S - Manual (Page 21)

WZ 3 20S User Guide 21
Gain Structure
How the levels between the different signal stages are set up is referred to as the
gain structure. For best performance it is important that the connected source
signals are matched to the ‘normal operating level’ of the console. Similarly the
levels of the connected amplifiers and destination equipment should be correctly
matched to the console outputs. If set too high then the signal peaks will be
clipped resulting in distortion, and if set too low then the signal-to-noise
performance will be degraded resulting in excessive background hiss and noise.
Using the Meters The MixWizard provides metering of inputs and outputs.
For best results operate the console with the main meters averaging around ‘0’
allowing the loudest moments to reach ‘+6’. Reduce the channel gain settings if
the red peak indicators start to flash. Note that the peak indicators light 5dB
before actual clipping to warn that you are nearing distortion and should reduce
gain. The LED bar meters have a ‘quasi-peak’ response with fast attack and slow
release so that fast musical transients are accurately displayed.
Matching a Source to the Console Start by turning down the channel
fader and send levels to prevent unexpected loud volumes reaching the main
speakers and monitors. Using PFL, adjust the GAIN control for an average ‘0’
reading on the console meters. These automatically switch to show the channel
pre-fade signal when PFL is pressed. Listen to the signal using headphones or
local AB monitor. Once the channel gain is correctly set you can raise the levels
to bring the channel into the mix. Note that you may need to adjust the gain if you
make significant changes to the EQ. Make sure that any equipment inserted into
the channel is set to operate around 0dBu line level. First set the gain with
inserted signal processors such as compressors switched to bypass.
Matching the Console to Destination Equipment The console
produces a standard XLR output level of +4dBu for a meter reading of ‘0’. It can
produce a maximum of +26dBu which is more than is usually required and
therefore gives you plenty of headroom. If you are connecting to a sensitive
power amplifier it is advisable to turn down its input trim control if the normal
console level is too high. Simply turning down the console output faders
degrades the output stage noise performance and reduces the resolution of the
fader movement. The output faders are best operated around ‘-10’ to ‘0’ for
loudest average volume required. This allows additional headroom if you need it.
Terminology The normal operating level is the optimum signal level for best
console performance, indicated by ‘0’ meter readings and resulting in the +4dBu
XLR output level. The channels operate at 0dBu and the mix stages at –2dBu for
extended headroom. Headroom is the extra level available above normal to allow
for loud peaks before the signal becomes clipped resulting in audible distortion.
The signal-to-noise ratio (SNR) is the difference measured in dB between normal
level and residual noise floor (hiss) produced by the console electronics. The
dynamic range is the sum of headroom and SNR representing the maximum
signal range possible from quietest to loudest.
Final word … A little care with setting gain structure throughout the signal
chain will give you the best performance and most manageable control of the mix.