E-Mu Ultraproteus Operation Manual page 93

PRESET PROGRAMMING
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.
THE Z-PLANE FILTER
In a simple UltraProteus filter, we would start with two complex filters and
interpolate between them using a single parameter. Refer to the diagram below.
Morph
B Filter
A Filter
Morph
Frequency
The UltraProteus Z-plane filter has the unique ability to change its function over time.
Filters A and B represent two different complex filters. By changing a single
parameter, the Morph, many complex filter parameters can now be changed
simultaneously. 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.
This Z-Plane filter sweep can be controlled by an envelope or function genera-
tor, an LFO, modulation wheels or pedals, keyboard velocity, key pressure, etc.
In fact, any of the modulation sources can control the Z-Plane filter.
Chapter 7: Preset Programming 89