Moog MP-201 Technical Information download pdf (Page 6)

In general, bright sounds have lots of strong overtones, while darker,

mellower sounds have fewer (and weaker) overtones.

A lter is a signal-modifying device that colors a sound by

emphasizing some parts of the audio spectrum and attenuating (cutting

down) other parts. In general, a lter has a quality of its own which is

superimposed on the tone color of the original 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 elements

in the music-making and sound design 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 - Filter Frequency Response

Figure 4 shows examples of the

frequency response characteristics

of two common types of lters:

(a) a 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 electronic music.

Each of them has its own distinct

sound, a large part of which is

directly related to the shape of its frequency response graph. The rst

type is the same as in the moogerfooger MF-101 lowpass lter, as well as

the lowest lter in the MIDI MuRF’s BASS voicing; the second type is

in the top 7 bands of the MIDI MuRF’s BASS voicing and all 8 bands of

the MIDS voicing.

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Moog MP-201 Technical Information Page 6