Apple Soundtrack Pro 3 - Manual (Page 273)

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 that 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.
EQ and Filter Effects
EQ is likely the most common audio effect used in post-production. You can use EQ to
shape the sound of a project by adjusting specific frequencies or frequency ranges. Using
EQ, you can create both subtle and extreme changes to the sound of your projects.
Most EQ effects make use of filters. As the name suggests, a filter allows certain frequencies
to “pass through” to the output while stopping or attenuating other frequencies. EQ
effects include highpass, lowpass, and band pass filters.
273 Chapter 10 Working with Audio Effects