Manual-4
Operation
e G4 has 3 modes: Gate, Ducker or downward Expander.
Side-chain Detector
e side-chain detector compares a reference signal, commonly
referred to as the key signal, to the reshold in order to deter-
mine the response of the Gate/Ducker/Expander. is 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 xed 35 ms averaging time con-
stant is used in Expand mode.
e look ahead detector works as follows: the main signal is
delayed, while the side-chain signal is not delayed. is delay is
extremely short (a few millionths of a second) and can’t be heard.
e G4 examines the signal in advance and determine the ap-
propriate response before an event (see Figures 2 and 3). is
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 xed 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.
e leading edge of the envelope is the attack time (0 to 250
ms). e hold time (0 to 3 seconds) determines how long the
gate remains open after the signal goes below the set threshold.
e release rate (25 ms to 2 seconds) determines how rapidly
the Gate closes after the hold time has expired.
e attack setting is equal to 3 time constants, or the time
it takes to reach 95% of the nal value. Because the attack is a
time constant, it takes the same period of time to reach 95 %
of nal value regardless of the Gate depth. is means the Gate
will open in the same period of time from a depth of 80 dB or
6 dB.
e minimum hold time is 25 ms and is based on two
parameters:
• e peak detector uses instantaneous attack and a xed
25 ms hold. is prevents cycle-to-cycle “chatter” at low
frequencies.
• e 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.
e release rate is in dB/sec. e 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 eectively closes the microphone in the
absence of the expected signal. Side-chain lters 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/o
• 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 o.
Figure 1: Gate Envelope
