Parametric Filters; The Z-Plane Filter - E-Mu Planet Phatt Operation Manual

PROGRAMMING BASICS

PARAMETRIC FILTERS

A more complex type of filter is called a parametric filter or Swept EQ.
A parametric filter allows control over three basic parameters of the
filter. The three parameters are: Frequency, Bandwidth, and Boost/Cut.
The Frequency parameter (Fc on Planet Phatt filters) allows you to
select a range of frequencies to be boosted or cut, the Bandwidth
parameter allows you to select the width of the range, and the Boost/
Cut parameter (Q on Planet Phatt filters) either boosts or cuts the
frequencies within the selected band by a specified amount.
Frequencies not included in the selected band are left unaltered. This
is different from a band pass filter which attenuates (reduces)
frequencies outside the selected band.
The parametric filter is quite flexible. Any range of frequencies can be
either amplified or attenuated. Often times, several parametric
sections are cascaded (placed one after another) in order to create
complex filter response curves.

THE Z-PLANE FILTER

The Z-plane filter can change its function over time. In a simple
Z-plane filter, we start with two complex filter types and interpolate
between them using a single parameter. Refer to the diagram below.
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.
Morph
B Filter
A Filter
Morph
Frequency
The Z-plane filter has the unique ability to change its function over time.
46 Planet Phatt Operation Manual