PRESONUS StudioLive24.4.2 Owner's Manual page 133

Owner's Manual
Expansion
Expansion— Terminology
Noise Gates
There are two basic types of expansion: dynamic and downward.
Expansion increases the dynamic range of a signal after the signal crosses
the expansion threshold. Dynamic expansion is basically the opposite
of compression. In fact, broadcasters use dynamic expansion to "undo"
compression before transmitting the audio signal. This is commonly
referred to as companding ' or COMPression followed by expANDING .
By far the most common use of expansion is downward expansion . In contrast
to compression, which decreases the level of a signal after it rises above the
compression threshold, expansion decreases the level of a signal after the
signal goes below the expansion threshold. The amount of level reduction is
determined by the expansion ratio. For example, a 2:1 expansion ratio reduces
the level of a signal by a factor of two. (e.g., if a level drops 5 dB below the
expansion threshold, the expander will reduce it to 10 dB below the threshold.)
Commonly used for noise reduction, expansion is very effective as a simple noise
gate. The major difference between expansion and noise gating is that expansion
is dependent on the signal level after the level crosses the threshold, whereas
a noise gate works independent of a signal's level beyond the threshold.
Downward Expansion. Downward expansion is the most common
expansion used in live sound and recording. This type of expansion
reduces the level of a signal when the signal falls below a set
threshold level. This is most common used for noise reduction.
Ratio. The expansion ratio sets the amount of reduction applied to a
signal once the signal has dropped below the expansion threshold. For
example, a 2:1 expansion ratio attenuates a signal 2 dB for every 1 dB it
drops below the threshold. Ratios of 4:1 and higher act much like a noise
gate but without the ability to tailor the attack, hold, and release times.
Threshold. The gate threshold sets the level at which the gate opens. Essentially,
all signals above the threshold setting are passed through unaffected, whereas
signals below the threshold setting are reduced in level by the amount set
by the range control. If the threshold is set fully counterclockwise, the gate is
turned off (always open), allowing all signals to pass through unaffected.
Attack. The gate attack time sets the rate at which the gate opens. A fast attack
rate is crucial for percussive instruments, whereas signals such as vocals and
bass guitar require a slower attack. Too fast of an attack can, on these slow-
rising signals, cause an artifact in the signal, which is heard as a click. All gates
have the ability to click when opening but a properly set gate will never click.
Hold. Hold time is used to keep the gate open for a fixed period after
the signal drops below the gate threshold. This can be very useful for
effects such as gated snare, where the gate remains open after the
snare hit for the duration of the hold time, then abruptly closes.
A Brief Tutorial on Dynamics Processing 8.2
Tutorials 8
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