Apple Soundtrack - Manual (Page 130)

130 Chapter 8 Working with Audio Effects
Roll-Off Filters
The simplest types of EQ effects are roll-off filters, which include lowpass, highpass,
bandpass, and shelf filters. Lowpass filters affect all frequencies above a specific
frequency, called the cutoff frequency. Frequencies above the cutoff are attenuated or
“rolled off” gradually, usually by a fixed number of decibels per octave. Highpass filters,
by contrast, affect all frequencies below their cutoff frequency. Bandpass filters exclude
all frequencies close to their center frequency. You can set the center frequency, and also
set the bandwidth or Q, which specifies how wide a range of frequencies around the
center frequency are affected.
These EQs include parameters for setting the cutoff frequency. Shelf filters add
parameters to control the gain (the amount of boost or cut). You can use roll-off filters
as “broad brush” effects to boost or cut a large range of frequencies.
Graphic EQs
Graphic EQs give you a set of filters (often with 10 or 31 filters), each with a set center
frequency and bandwidth. Using a graphic EQ, you can shape a wide variety of
frequencies throughout the frequency range. Graphic EQs can be used to shape the
sound of the overall project mix.
Parametric EQs
Parametric EQs are similar to bandpass EQs, but provide a greater amount of control,
and can be used for extremely precise adjustments. With a parametric EQ, you can set
the center frequency, the gain, and the bandwidth. Used carefully, a parametric EQ can
help a track cut through the mix, or help a track or project sound fuller. Parametric EQs
can also be used to remove specific, unwanted frequencies from a mix.