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7 - Synthesizer Basics

Dynamic Filters

116 Proteus VX Operation Manual

The Z-Plane Filter

A Z-plane filter is a filter which can change its function over time. In a Z-plane filter, we

start with two complex filter types and interpolate between them using a single

parameter. Refer to the diagram below.

The Z-plane filter has the unique ability to change its function over time.

Filters A and B represent two different complex filters or “frames”. By changing a single

parameter, the Morph, many complex filter parameters can now be changed simulta-

neously. Following along the Morph axis you can see that the filter response smoothly

interpolates between the two filters. This is the essence of the Z-plane filter. Through

the use of interpolation, many complex parameters are condensed down into one

manageable entity.

Consider, as an example, the human vocal tract, which is a type of complex filter or

resonator. There are dozens of different muscles controlling the shape of the vocal

tract. When speaking, however, we don't think of the muscles, we just remember how it

feels to form the vowels. A vowel is really a configuration of many muscles, but we

consider it a single object. In changing from one vowel to another, we don't need to

consider the frequencies of the resonant peaks! You remember the shape of your

mouth for each sound and interpolate between them. This is similar to what the Z-

plane filter does.

This Z-plane filter sweep can be controlled by an envelope generator, an LFO,

modulation wheels or pedals, keyboard velocity, key pressure, etc. In fact, any of the

modulation sources can control the Z-plane filter.

Frequency

Amplitude

Morph

B Filter

A Filter

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E-Mu PROTEUS FX Manual de usuario Pagina 116