PRESONUS StudioLive 24.4.2 Owner's Manual page 151

Owner's Manual
8.2.2 Types of Dynamic Processing
Compression/Limiting
Punch, apparent loudness, presence—these are just three of the many
terms used to describe the effects of compression/limiting.
Compression and limiting are forms of dynamic-range (gain) control. Audio
signals have very wide peak-to-average signal-level ratios (sometimes
referred to as dynamic range, which is the difference between the loudest
level and the softest level). The peak signal can cause overload in the audio-
recording or sound-reinforcement chain, resulting in signal distortion.
A compressor/limiter is a type of amplifier in which gain is dependent on the
signal level passing through it. You can set the maximum level a compressor/
limiter allows to pass through, thereby causing automatic gain reduction
above some predetermined signal level, or threshold. Compression refers,
basically, to the ability to reduce, by a fixed ratio, the amount by which a
signal's output level can increase relative to the input level. It is useful for
lowering the dynamic range of an instrument or vocal, making it easier to
record without distorting the recorder. It also assists in the mixing process by
reducing the amount of level changes needed for a particular instrument.
Take, for example, a vocalist who moves around in front of the microphone while
performing, making the output level vary up and down unnaturally. A compressor
can be applied to the signal to help correct this recording problem by reducing
the louder passages enough to be compatible with the overall performance.
How severely the compressor reduces the signal is determined by the compression
ratio and compression threshold. A ratio of 2:1 or less is considered mild
compression, reducing the output by a factor of two for signals that exceed
the compression threshold. Ratios above 10:1 are considered hard limiting.
As the compression threshold is lowered, more of the input signal is
compressed (assuming a nominal input-signal level). Care must be taken
not to overcompress a signal, as too much compression destroys the
acoustic dynamic response of a performance. (That said, overcompression
is used by some engineers as an effect, with killer results!)
Limiting refers to the processing that prevents the signal from getting any louder
(that is, it prevents any increase in the signal's amplitude) at the output.
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 the level is increased, the kick drum stays lost in the "mud. " A
touch of compression can 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 (normally
the loudest portions of the signal) can be far outside the average level of the
vocal signal. Because the level can change continuously and dramatically, 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 Brief Tutorial on Dynamics Processing
Tutorials 8
8.2
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