3.1 BASIC IDEAS AND APPLICTIONS
Why Do You Need Noise Gates?
Problems arise when there is noise or instruments in the background of the vocal mic that became more audible after the
lower end of the dynamic range was raised. (air conditioner, loud drummer, etc.) You might attempt to mute the vocal
between phrases in an attempt to remove the unwanted signals; however this would probably be disastrous. A better
method is to use a noise gate. The noise gate threshold could be set at the bottom of the dynamic range of the vocal, say -
10dBu, such that the gate would ‘close’ out the unwanted signals between the phrases. If you have ever mixed live you
know well the problem cymbals can add to your job by bleeding through your tom mics. As soon as you add some highs to
get some snap out of the tom the cymbals come crashing through, placing the horn drivers into a small orbit. Gating those
toms so that the cymbals no longer ring through the tom mics will give you an enormous boost in cleaning up the overall
mix.
Expansion
There are two basic types of expansion:
dynamic
and
downward
. Expansion increases the dynamic range or level of a signal
after the signal crosses the expansion
threshold.
Dynamic expansion is basically the opposite of compression. In fact,
broadcasters use dynamic expansion to
‘undue’ compression before transmitting the audio signal. This is commonly referred to as ‘companding’ or COMPression
followed by expANDING. By far the most common use of expansion is
downward
expansion. In contrast to compression,
which decreases the level of a signal after rising above the
compression threshold
, expansion decreases the level of a signal
after the signal goes below the
expansion threshold
. The amount of level reduction is determined by the expansion ratio.
For example, a 2:1 expansion ratio reduces the level of a signal by a factor of two. (e.g. if a level drops 5dB below the
expansion threshold, the expander will reduce it to 10dB below the threshold.) Commonly used as noise reduction,
expansion is very effective as a simple noise gate.
The major difference between expansion and noise gating is the fact that expansion is
dependent
on the signal level after
crossing the threshold, whereas a noise gate works
independent
of a signal’s level after crossing the
threshold.
Noise Gating
Noise gating is the process of removing unwanted sounds from a signal by attenuating all signals below a set
threshold
. As
described above, the ‘gate’ works independent of the audio signal after being ‘triggered’ by the
signal crossing the gate threshold. The gate will remain open as long as the signal is above the threshold. How fast the gate
opens to let the ‘good’ signal through is determined by the
attack
time. How long the gate stays open after the signal has
gone below the threshold is determined by the
hold
time. How fast the gate closes is determined by the
release
. The range
determines how much the gate attenuates the unwanted signal while closed.
Patching Using a Patch Bay
When using a patch bay to extend the GTX44's patch panel for easier access, the following should be considered:
1. Lowest noise is achieved when using balanced patch bays.
2. The input and output jacks should not be normalled (the send routed
back to the return).
3. The sidechain jacks must be normalled.
Gating Drums or Percussion Instruments
Adjust the Gate on the snare to stop those other drums from 'bleeding' through the snare mic: Turn the gate release knob
to about the middle position, turn the gate attack knob to fully counter-clockwise, set the gate range to -60dB, adjust the
