TECHNICAL INFORMATION
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PreSonus 2007
Compressor / Limiters are commonly used for many audio applications. For example:
A kick drum can get lost in a wall of electric guitars. No matter how much level is increased, the
kick drum stays ‘lost in the mud’. Add a touch of compression and tighten up that kick drum sound
allowing it to ‘punch’ through without having to crank the level way up.
A vocal performance usually has a wide dynamic range. Transients (the very loudest portion of the
signal) can be far outside the average level of the vocal signal. It is extremely difficult to ride the
level with a console fader. A compressor/limiter automatically controls gain without altering the
subtleties of the performance.
A solo guitar can seem to be masked by the rhythm guitars. Compression can make your ‘lead’ soar
above the track without shoving the fader through the roof.
Bass guitar can be difficult to record. A consistent level with good attack can be achieved with
proper compression. Your bass doesn’t have to be washed out in the low end of the mix. Let the
compressor/limiter give your bass the punch it needs to drive the bottom of the mix.
Expansion
There are two basic types of expansion: dynamic and downward. Expansion increases the dynamic range or
level 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 ‘undue’ 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 rising 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 5dB below the expansion threshold, the expander will reduce it to 10dB below the threshold.)
Commonly used as noise reduction, expansion is very effective as a simple noise gate. The major difference
between expansion and noise gating is the fact that expansion is dependent on the signal level after crossing
the threshold, whereas a noise gate works independent of a signal’s level after crossing the threshold.
Noise Gating
Noise gating is the process of removing unwanted sounds from a signal by attenuating all signals below a set
threshold. As described above, the ‘gate’ works independent of the audio signal after being ‘triggered’ by the
signal crossing the gate threshold. The gate will remain open as long as the signal is above the threshold.
How fast the gate opens to let the ‘good’ signal through is determined by the attack time. How long the gate
stays open after the signal has gone below the threshold is determined by the hold time. How fast the gate
closes is determined by the release. How much the gate attenuates the unwanted signal while closed is
determined by the range.
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