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Tour 3
Dynamic
Processing
Tip: When the filter cutoff is set to 0 Hz,
the sound will be completely cut off. The
initial filter cutoff and all filter Fc modulators
ADD algebraically to determine the actual Fc.
If you are not getting sound, adjust the initial
Fc or reduce the amount of modulation.
Careful adjustment of the filter parameters is
the secret of getting great sounds.
Low Q
Med Q
High Q
Frequency
Turning up the "Q" will emphasize the
frequencies around the cutoff point.
The Dynamic Processing module consists of several interesting sound
processing functions. Let' s start with the Filter and VCA sections, as they
are among the most important.
The VCA function contains a Voltage Controlled Amplifier that controls
the amplitude envelope of a sound. The filter function contains a Voltage
Controlled Filter that controls the timbre of a sound. (Note: The voltage
controlled filters and amplifiers are actually implemented digitally.)
Working with the Filter
A filter is a device which allows you to remove certain components of a
sound depending on its frequency. For example, a Low Pass Filter, like
the one in ESI-32, lets the low frequencies pass and removes only the
high frequencies.
100
80
Output of Filter
60
40
20
40
The point at which the frequencies begin to be cut is called the Cutoff
Frequency (or Fc for short). A filter that lets only the high frequencies
pass would be called a High Pass filter. Using a filter, we now have a way
to control the harmonic content of a sampled sound. As it turns out, a
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.
The VCF envelope generator is used to control the cutoff frequency of
the low pass filter. This allows the frequency content to be varied
dynamically over the course of the note. Dynamic filtering coupled with
different samples makes for endless possibilities in the final sound.
Another control on the low pass filter is called Q or resonance. Turning
up the Q of the filter tends to emphasize the frequencies around the
cutoff frequency. In terms of sound, frequencies around the cutoff will
tend to "ring" with high Q settings. If the filter is swept back and forth
slowly with a high Q, various overtones will be "picked out" of the
sound and amplified as the resonant peak sweeps over them. Bells and
gongs are real world examples of sounds which have a high Q.
Cutoff Frequency
80
160
360
720
1440 2880
Frequency
...
35
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