Manual-4
Operation
The G4 has 3 modes: Gate, Ducker or downward Expander.
Side-chain Detector
The side-chain detector compares a reference signal, commonly
referred to as the key signal, to the Threshold in order to deter-
mine the response of the Gate/Ducker/Expander. This reference
signal may be a version of the main input (Internal side-chain)
or another signal altogether (using the External side-chain
inputs).
Two types of detection are used in the G4:
• Peak
detection is used in
Gate
and
Duck
modes to accurately
capture and reproduce transients.
• True rms
detection with a fixed 35 ms averaging time con-
stant is used in
Expand
mode.
The look ahead detector works as follows: the main signal is
delayed, while the side-chain signal is not delayed. This delay is
extremely
short (a few millionths of a second) and can’t be heard.
The G4 examines the signal in advance and determine the ap-
propriate response
before
an event (see Figures 2 and 3). This
action allows the
Gate
and
Ducker
to turn on
before
a transient
occurs. Pre-ramping the signal allows the main signal to be
gated-on as the signal reaches the threshold.
Look ahead pre-ramping serves two purposes:
• Leading edge wave shape is preserved above 1 kHz (see
Figure 2).
• It is possible to tighten up the sound of frequencies below
1 kHz
without
the annoying click resulting from deep gate
depth, high threshold and instantaneous attack settings (see
Figure 3).
Gate Mode
A Gate operates by turning a signal down a fixed number of
dB (known as depth) when the key signal drops below a set
threshold.
Figure 1 shows the waveform and envelope of a gated signal.
The leading edge of the envelope is the
attack
time (0 to 250
ms). The
hold
time (0 to 3 seconds) determines how long the
gate remains open after the signal goes below the set threshold.
The
release
rate (25 ms to 2 seconds) determines how rapidly
the Gate closes after the hold time has expired.
The
attack
setting is equal to 3 time constants, or the time
it takes to reach 95% of the final value. Because the attack is a
time constant, it takes the same period of time to reach 95 %
of final value regardless of the Gate depth. This means the Gate
will open in the same period of time from a depth of 80 dB or
6 dB.
The minimum
hold
time is 25 ms and is based on two
parameters:
• The peak detector uses instantaneous attack and a fixed
25 ms hold. This prevents cycle-to-cycle “chatter” at low
frequencies.
• The hold time
after
detection is adjustable from 0 ms to 3
seconds, giving a minimum hold time of 25 ms and a maxi-
mum hold time of 3.025 seconds.
The
release
rate is in dB/sec. The front panel setting refers
to the length of time it takes to ramp 10 dB. If the release rate is
set to 250 ms, then it takes: 250 ms to ramp 10 dB, 125 ms to
ramp 5 dB and 2 seconds to ramp 80 dB.
Gating Uses
1. To reduce microphone bleed, handling noise, electrical hum
or incidental back ground noise. Microphones continue to
pick up extraneous noise even when the intended signal is
not present. A Gate effectively closes the microphone in the
absence of the expected signal. Side-chain filters further help
identify intended versus extraneous content by limiting the
frequency response to the frequencies of interest.
Example uses
• Clean up bleed between drum microphones
• Automatically gate speech microphones on/off
• Silence noisy guitar amps between songs.
2. To modify the sound of an instrument. To soften the sound,
use a longer attack, lower threshold and/or reduced depth. To
tighten up the sound, use a shorter attack, higher threshold
and/or increased depth.
Example uses
• Fast attack settings tighten the sound of a drum or percus
-
sion instrument.
• Short hold and fast release times give that ultra-cool 80’s Phil
Collins drum sound.
3. To synchronize two sounds. Use the external side-chain
inputs to key one input based on an a secondary input.
Example uses
• Attach a piezo transducer to a drum and use it as an external
side-chain input to accurately gate the drum mic on and off.
Figure 1: Gate Envelope
