E-Mu PROTEUS FX Bedienungsanleitung PDF herunterladen (Seite 114)

7 - Synthesizer Basics

Dynamic Filters

114 Proteus VX Operation Manual

A Notch Filter is just the opposite of a bandpass filter and is used to eliminate a narrow

band of frequencies.

Another control found on traditional filters is called Q or resonance. A lowpass filter

with a high Q would emphasize the frequencies around the cutoff frequency. The

following chart shows how different amounts of Q affect the low pass filter response.

In terms of sound, frequencies around the cutoff tend to “ring” with high Q settings. If

the filter is slowly swept back and forth, with a high Q, various overtones are “picked

out” of the sound and amplified as the resonant peak sweeps over them. Bells and

gongs are real world examples of sounds which have a high Q.

Another characteristic of a filter is the number of poles it contains. Traditional synthe-

sizer filters were usually either 2-pole or 4-pole filters. The Proteus has a selectable 2, 4

or 6-pole low pass filter. The number of poles in a filter describes the steepness of its

slope. The more poles, the steeper the filter's slope and the stronger the filtering action.

The tone controls on your home stereo are probably one-pole or two-pole filters.

Parametric equalizers are usually either two-pole or three-pole filters. In terms of

vintage synthesizers, Moog and ARP synthesizers used 4-pole filters. Oberheim and E-

mu synthesizers were famous for their 2-pole filter sound.

Using a filter, we now have a way to control the harmonic content of a sampled sound.

As it turns out, even a simple low pass filter can simulate the response of many natural

sounds.

For example, when a piano string is struck by its hammer, there are initially a lot of

high frequencies present. If the same note is played softer, there will be fewer of the

high frequencies generated by the string. We can simulate this effect by routing

keyboard velocity to control the low pass filter. The result is expressive, natural control

over the sound.

Frequency

Amplitude

Low Q Med Q High Q

Frequency

Amplitude

4-pole

Lowpass

6-pole

Lowpass

2-pole

Lowpass

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E-Mu PROTEUS FX Bedienungsanleitung Seite 114