E-Mu Xtreme Lead-1 Specifications download pdf (Page 114)

114 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

B Filter

A Filter

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E-Mu Xtreme Lead-1 Specifications Page 114