PRESONUS StudioLive 24.4.2 Owner's Manual page 67

8 Tutorials
8.2 A Brief Tutorial on Dynamics Processing
Limiter. A limiter is a compressor that is set to prevent any increase in the level of a
signal above the threshold. For example, if you have the threshold knob set at 0 dB,
and the ratio turned fully clockwise, the compressor becomes a limiter at 0 dB, so
that the output signal cannot exceed 0 dB regardless of the level of the input signal.
Attack. Attack sets the speed at which the compressor acts on the
input signal. A slow attack time allows the beginning envelope of a
signal (commonly referred to as the initial transient ) to pass through the
compressor unprocessed, whereas a fast attack time immediately subjects
the signal to the ratio and threshold settings of the compressor.
Release. Release sets the length of time the compressor takes to return the
gain reduction back to zero (no gain reduction) after the signal level drops
below the compression threshold. Very short release times can produce
a very choppy or "jittery" sound, especially in low-frequency instruments
such as bass guitar. Very long release times can result in an overcompressed
sound; this is sometimes referred to as "squashing" the sound. All ranges
of release can be useful at different times, however, and you should
experiment to become familiar with the different sonic possibilities.
Hard/Soft Knee. With hard-knee compression, the gain reduction applied to the
signal occurs as soon as the signal exceeds the level set by the threshold. With soft-
knee compression, the onset of gain reduction occurs gradually after the signal
has exceeded the threshold, producing a more musical response (to some folks).
Auto. Places a compressor in automatic attack and release
mode. The attack and release knobs become inoperative and
a preprogrammed attack and release curve is used.
Makeup Gain. When compressing a signal, gain reduction usually results
in an overall reduction of level. The gain control allows you to restore
the loss in level due to compression (like readjusting the volume).
Compressor Sidechain. The sidechain jack interrupts the signal that the
compressor is using to determine the amount of gain reduction it should apply.
When no connector is inserted into this jack, the input signal goes directly to the
compressor's control circuitry. When a connector is inserted into this jack, the
signal path is broken. The control signal can then be processed by an equalizer,
for example, to reduce sibilance (de-essing) in a vocal track. The control signal
is then returned to the unit via the connector. One common application for
a sidechain is when using a compressor to reduce the level of music or other
background sound whenever a narrator speaks or vocalist sings, allowing the
voice to be clearly heard. In this application, the vocal signal is routed to the
sidechain input, while the music is routed through the main compression
circuitry. Now the compressor will automatically duck—that is, reduce the
level of—the music whenever the narrator speaks or the vocalist sings.
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PreSonus StudioLive ™ 24.4.2 Owner's Manual
Expansion
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.
Expansion— Terminology
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.
Noise Gates
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.
Tutorials 8
A Brief Tutorial on Dynamics Processing 8.2
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