Apple Soundtrack Pro 2 - Manual (Page 333)

Chapter 11 Working with Audio Effects 333
Compressors can also include parameters for attack and release. These parameters let you
set how quickly the compressor reacts once the threshold is reached (for attack) or once
the signal falls below the threshold again (for release). Use these parameters to make the
compressor’s effect more subtle or more pronounced. Another parameter on some
compressors is the knee (or soft knee), which lets you control how gradually the compressor
transitions between no compression and the compression ratio at the threshold.
Compressors are typically used on vocal tracks to make the vocals prominent in the
overall mix. They can also be used on music and sound effects tracks, but are rarely
used on ambience tracks.
Limiters
Limiters (also called peak limiters) prevent the audio signal from exceeding a maximum
volume level. A compressor gradually attenuates levels above the threshold, but a
limiter puts a hard limit on any signal louder than the threshold, usually at a high ratio.
You use a limiter mainly to prevent clipping.
Noise Gates
A noise gate alters the signal in the opposite direction from a compressor. While a
compressor lowers the volume of sounds above the threshold, a noise gate lowers the
sounds below the threshold. Loud signals pass through unchanged, but softer signals,
such as the decay of a loud instrument, are cut off. Noise gates can be used to
eliminate low-level noise or hum from an audio signal.
Distortion Effects
Distortion effects simulate the sound of analog and digital distortion. After working to
eliminate the digital distortion caused by clipping from a project, why would you add
distortion as an effect? The distortion produced by overdriven vacuum tubes (which
were used in amplifiers and music recording equipment before the development of
digital recording technology) produces an effect which many people find pleasing, and
which is integral to many styles of popular music. Analog tube distortion adds a
distinctive warmth and bite to the signal.
There are also distortion effects which intentionally cause clipping and digital
distortion of the signal. These can be used to modify vocal, music, and other tracks to
produce an intense, unnatural effect, or for creating sound effects.
Distortion effects include parameters for tone, which let you shape the way in which
the distortion alters the signal, and for gain, which let you control how much the
distortion increases the output level of the signal.