Drawmer Tourbuss for Digidesign Venue - Manual (Page 9)

TOURBUSS operator’s manual
9
Noise Gate Operation
There are circumstances when the programme material is corrupted such as, in a multi-miked drum kit setup,
some hi-hat will inevitably leak into the snare microphone, some snare drum into the kick drum microphone
and so on. Equally, on location, you may experience problems due to wind or traffic noise or close-by
conversation. If the unwanted noise is different in pitch to the wanted sound, it is often possible, by using the
Key Listen facility, to use the filters to ‘tune’ in to the wanted sound while excluding the unwanted.
With signals having a naturally slow or moderate attack, setting the gate attack time too fast can cause
clicks, particularly if the threshold has to be set high because of excessive background noise, especially with
the audio signal in lower frequencies (eg bass guitar, bass drum). With a high threshold, a low frequency sine
wave will be ignored as the signal starts from its zero level point, as this wave climbs towards its peak, the
level will suddenly exceed the threshold setting, at this point a very fast attack rate will switch the signal
through the noise gate with such a steep (almost vertical) leading edge that the low frequency sound will have
a single high frequency square wave added to its first cycle, in other words a ‘click’ will be heard. In cases like
these, start with a fast attack time and moderate threshold, then gradually lengthen the attack time until the
audible click just disappears when the gate opens, unless the ‘click’ is being added as an effect!
Ducking
Probably the most common form of Ducking is that used by radio announcers, whereby the volume of the
music being played is dropped, enabling them to speak over it. In Duck mode the music signal is routed to the
input and the announcer’s microphone signal is the key source ( set ‘Ext/Int’ to ‘External’).
The Range control is used to set the level to which the music will drop duck is triggered, and the envelope
controls determine the rate at which the level will drop and then recover. It is usual to select a fairly fast Attack
time, with a slow Release time of a second or so - this will react quickly and then bring the music level back
up slowly and smoothly, and is hence less disconcerting to the listener. This same technique can be used to
reduce the level of other instruments during a solo.
Difficult Material To Gate
If noise contamination is serious enough to be evident even during moderately loud programme material, then
simple gating will do little to help. Indeed, the very fact that the Gate produces silence during pauses can
make the noise content of the programme material even more apparent. In extreme cases restricting the
Range of the Gate to about -15dB will adequately reduce the noise during pauses but not too dramatically.
Where the wanted signal does not occupy the full audio spectrum the Key filters may also be used to good
effect. Taking the example of the electric guitar, this produces little below 100Hz or above 3kHz so setting the
Gate to Key Listen mode will enable you to use the filters to exclude much of the amplifier hum at the low end
and hiss at the top end while having little effect on the sound of the guitar. Surprisingly, the same is true of the
acoustic guitar; (even a bright-sounding steel-strung model), and the filters can be used to reduce the effect
of string squeak or the player’s breathing.
Quick Start
Setting of controls can be done very quickly using
the following suggestions:
Select the Key trigger source using the Key
section.
Initially, the LF filter should be set fully
anticlockwise, with HF fully clockwise. This will
allow the full audio spectrum of the Key input
programme to be monitored. Set the Range
control fully anticlockwise and the Key Listen
selector switch to Normal.
Set the Attack, Hold. Decay and Range
controls. For a programme with long legato
release, then Release will also need to be long,
e.g. Piano with reverb. For material with much
low frequency content, the Attack will need to
be quite slow, unless a ‘click’ is desired.
With the Release control set at its midway
position, and with suitable programme material
fed into the Gate module, increase the Threshold
level from its anticlockwise position until the Gate
starts to operate. This will be shown by the
activity of the traffic light LED’s, the threshold
meter, and you should also hear the effect on
the output signal, in that pauses in the
programme will now be silent.
Adjust the settings: If the Threshold setting is
too high, the Gate will start to cut out wanted
pieces of programme, so adjust it to as low a
setting as possible. If the ends of sounds are
being truncated, then a longer Decay time may
help. On the other hand, if unwanted noise is
audible after the wanted sound has ended, a
shorter Decay time may be more appropriate.
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