TECHNICAL INFORMATION
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PreSonus 2007
Compressor Sidechain. The sidechain jack interrupts the signal that the compressor is using to
determine the amount of gain reduction to 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. This signal can then be processed by an equalizer for example to
reduce sibilance (de-essing) in a vocal track. The signal is then returned to the unit via the
connector. The signal returned to the sidechain could be that of a narrator or vocalist. In this
application, the audio that is passing through the compressor will automatically ‘duck’ when the
narrator speaks or vocalist sings.
Expanders
Downward Expansion. Downward expansion is the most common expansion used in pro audio and
recording. This type of expansion applies noise reduction to all signals below a set threshold level.
Ratio. The expansion ratio sets the amount of noise reduction applied to a signal once the signal has
dropped below the expansion threshold. For example, a 2:1 expansion ratio attenuates a signal 2dB
for every 1dB it drops below the threshold. Ratio’s 4:1 and higher act much like a noise gate 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 counter-
clockwise, 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 producing an
audible ‘click’. All gates have the ability to ‘click’ when opening, however a properly set gate will
never click. Below is an example of a gate opening very fast on a pure sine wave. Notice the almost
vertical edge of the waveform when the gate opens. This is what produces the high frequency artifact
known as ‘click’.
Hold. Hold time is used to keep the gate open for a fixed period of time following the signal going
below the gate threshold. This can be really 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.
Release. The gate release time determines the rate at which the gate closes. Release times should
typically be set so that the natural decay of the instrument or vocal being gated is not affected.
Shorter release times help to clean up the noise in a signal but my cause ‘chattering’ in percussive
instruments. Longer release times usually eliminate ‘chattering’ and should be set by listening
carefully for the most natural release of the signal.
Range. The gate range is the amount of gain reduction that the gate closes down to. Therefore, if the
range is set at 0dB, there will be no change in the signal as it crosses the threshold. If the range is
set to -60dB, the signal will be gated (reduced) by 60dB, etc.
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