Table of Contents
Advertisement
9 - Synthesizer Basics
Dynamic Filters
If an envelope generator is used to control the cutoff frequency of a filter, the frequency
content can be varied dynamically over the course of the note. This can add animation
to the sound as well as simulate the response of many natural instruments.
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 Gain. The Frequency parameter 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 Gain parameter 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.
+18 dB
Boost
0 dB
Cut
-18 dB
Another parameter sometimes used on a parametric filter is Shelving. Shelving simply
widens the passband so that it extends to the limit of the upper or lower frequency
range.
The parametric filter is quite flexible. Any range of frequencies can be either amplified or
attenuated. Several parametric sections are often cascaded in order to create complex
filter response curves.
If four parametric filter sections were cascaded, it would be possible to create the
following complex filter response.
4 Parametric Equalizers
20
15
10
5
0
-5
500
Linear Frequency - Hertz
Many natural instruments have complex resonances which are based on their sound-
board or tube size. The resonance shown above would be impossible to create using a
normal synthesizer filter.
156
Freq.
Bandwidth
Frequency
10,000
15,000
20,000
Parametric
Filter
Proteus X Operation Manual
Advertisement
Table of Contents
