Manual-5
Figure 2: Look ahead pre- ramping (3 kHz signal)
In the above waveform, the side-chain Gate threshold equals
the peak sine wave value (first vertical marker). The main input
signal (yellow trace) is delayed a few microseconds. At 3 kHz,
the exponential look-ahead ramp guarantees the first cycle is
fully gated on as it reaches the threshold level (second vertical
marker). The look ahead and analog converter delays give a total
propagation delay though the G4 of 1.62 ms, an imperceptible
amount.
Expand Mode
The basic objective of expansion is the same as gating: expand
the dynamic range of a signal by reducing the noise floor.
However, an expander provides a more subtle response than a
gate in applications requiring smooth, natural decay. It works by
controlling the
ratio
of output change to input change, in effect
dynamically modifying gain below a set threshold. For example,
if the ratio is set to 4:1 then the output decreases 4 dB for every
1 dB of decrease in input level (See figure 4).
Compared to gating, expansion typically uses a slower attack
time and longer release time.
Example uses
• Enhance the long, gradual decay of a piano or guitar.
• Use an expander on a quiet vocalist to reduce stage noise
between passages.
Figure 3: Look ahead pre-ramping (500 Hz signal)
At 500 Hz the exponential pre-ramp ensures that the first cycle
is properly gated on. Look ahead pre-ramping produces a more
natural leading edge to the wave form, tightening up the sound
without the harsh click that occurs with an instantaneous rise
time.
Figure 4: Gate vs. Expander
The above graph shows the difference between Gate and
Expander operation. The solid red trace shows the side-chain
input.
Gate:
The green long-dash trace shows the operation of a
Gate. The Gate attenuates the signal by a fixed number of dB
when the signal is below threshold. The response is adjustable
over a wide range using Attack, Release and Hold controls. It
is possible to achieve natural decay with string instruments by
setting the release for slow ramp down. Fast attack, quick release
and deep depth settings can be used to change the character of
drums or other percussion instruments.
Expander:
The blue short-dash trace shows downward ex-
pansion with a ratio of 2:1. The signal is turned down gradually,
resulting in lower noise in the absence of signal while allowing
natural signal decay. Downward expansion generally uses a Re-
lease time of about 500 ms to 1 second and an Attack setting of
100 ms to 500 ms. The Hold function is not active when using
the Expander.
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INPUT dBu
SIDE-
CHAIN INPUT
GATE
EXPANDER
THRESHOLD = 0 dBu
O
U
T
P
U
T
d
B
u
