BSS Audio OPAL Series DPR-944 Owner's Manual - Manual (Page 17)

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7.0 General guide to gating
7.1 What are gates
for?
Put simply, a noise gate is a device that blocks or switches off a signal, if that
signal falls below a certain preset level. This works because the ear is much
more sensitive to noise in the absence of other signals. Originally noise gates
were used for just that, gating or removing noise from recordings. For
example, traffic rumble in studios, or noise from old tape loop echo chambers.
Figure 7.1 shows a pre-gated signal (input) with background noise present, and
also the user set threshold. Figure 7.2 shows the signal after being gated by a
crude gate. The background noise has been removed.
General guide to gating
Noise gates, or gates, function by taking the main input signal and splitting it
into two paths. One path passes through an electronic switch to the output and
is not modified in any other way. The other, called the key signal is processed
to provide a ‘trigger’ for the switch. Once the main signal has exceeded the
user selected threshold and provided the trigger, the gate will open. In modern
gates the switch is replaced by a fader circuit, thereby allowing the gated
signal to be faded up and down, often quite slowly. The fade up rate is
defined by an attack control, the fade down by a release control. This fading
action can be important, as the ear is much more sensitive to abrupt changes
in level than gradual ones.
One major application for modern advanced gates is the separation of sounds
so that they may be processed separately, for example in a multi-miked drum
kit. In this case each drum would have a separate microphone, the intention
being to have independent control of the level and tonal balance of each
drum. Unfortunately, due to the close proximity of the microphones, there will
be significant bleed of sound from one drum to another. Gates are used to
Fig 7.1 Noisy signal
Fig 7.2 Noisy signal
after being gated