122 E-MU Systems
Programming Basics
Dynamic Filters
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. See the following diagram.
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.”
Changing a single parameter, the Morph, changes many complex filter
parameters 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 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 Z-plane filter sweep can be controlled by an envelope generator, an
LFO, modulation wheels or pedals, keyboard velocity, key pressure, and so
on. In fact, any of the modulation sources can control the Z-plane filter.
Because creating the complex filtering is difficult and very time consuming,
we have created 50 different filters and installed them permanently in ROM
for your use. You simply select and use the filters in a manner similar to
choosing an instrument. Because there are so many types of instruments
and filters to choose from, the number of possible permutations is
staggering.
Frequency
Amplitude
Morph
Morph
B Filter
A Filter
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General