Chapter 7: Preset Programming 87
PRESET PROGRAMMING
Using a filter, we now have a way to control the harmonic content of
a sampled sound. As it turns out, even a simple low pass filter can
simulate the response of many natural sounds.
For example, when a piano string is struck by its hammer, there are
initially a lot of high frequencies present. If the same note is played
softer, there will be fewer of the high frequencies generated by the
string. We can simulate this effect by routing the velocity of the
keyboard to control the amount of high frequencies that the low pass
filter lets through. The result is expressive, natural control over the
sound.
If an envelope generator is used to control the cutoff frequency of a
low pass 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. A parametric
filter gives you control over three basic parameters of the filter. The
three parameters are: Frequency, Bandwidth, and Boost/Cut. The Fre-
quency 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 Boost/Cut parameter either boosts or cuts
the frequencies within the selected band by a specified amount. Fre-
quencies 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.
Boost
Cut
Freq.
0 dB
+18 dB
-18 dB
Bandwidth
Frequency
Amplitude
Parametric
Filter
The parametric filter is quite flexible. Any range of frequencies can be
either amplified or attenuated. Often times, several parametric sec-
tions are cascaded (placed one after another) in order to create com-
plex filter response curves.
To Next Page
Loading...
Need help?
General
