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Chapter 11 Working with Audio Effects 335
Note: The frequencies shown for each range are approximate. Any division of sound
into frequency ranges is somewhat arbitrary, and is meant only to give a general
indication of each range.
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 is 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.
High Midrange 1.2–2.5 kHz Includes the consonants of voices and the high
harmonics of musical instruments, especially
brass instruments. Excessive boosting in this
range can create a pinched, nasal sound.
Midrange 750 Hz–1.2 kHz Includes the vowels of voices and the harmonics
of musical instruments that create tone color.
Low Midrange 250–750 Hz Includes the fundamentals and lower harmonics
of voices and musical instruments; careful EQing
of each can keep them from competing.
Excessive boosting in this range can result in
muddy and unclear audio; excessive cutting can
produce thin-sounding audio.
Bass 50–250 Hz Corresponds roughly to the bass tone control
on a stereo. Includes the fundamental
frequencies of voices and of musical
instruments. Excessive boosting in this range
can sound boomy and thick.
Low Bass 50 Hz and below Also called sub bass. Very little of the sound of
voices or musical instruments falls in this range.
Many sound effects used in movies, such as
explosions and earthquakes, fall in this range.
Name Frequency range Description