sound. Some types of lters (like the bass and treble controls on
your sound system) have subtle, gentle effects on a sound’s timbre.
Other types of lters have stronger and more dramatic effects, and
are frequently used as vital elements in the music-making process.
Strong lters include phasers, angers, and wah-type resonant
lters.
A graph showing what a lter does is called the lter’s frequency
response. The horizontal axis is frequency. The vertical axis is the
lter’s gain. A gain of “1” (unity) means that, at that frequency, the
output of the lter is just as strong as the input. A gain of less than
unity means that the lter’s output is attenuated at that frequency,
while a gain of greater than unity means that the output is actually
greater than the input.
Figure 4 shows examples of the frequency response
characteristics of two common types of lters: (a) a shelving
lowpass lter, which passes frequencies without attenuation up to a
so-called ‘cutoff frequency’, and attenuates the frequencies above
cutoff; (b) a resonant lter, which emphasizes frequencies around
the lter’s ‘center frequency’.
Both of these lter types are widely used in contemporary music
performance. Each of them has its own distinct sound, a large part
of which is directly related to the shape of its frequency response
graph. A cut-off lter is used at the lowest effected frequency of
the MF105B. The remaining seven lters are all resonant lters.
33.
Figure 4 - Frequency responses of typical lters.
