X

Chapter 8 EVOC 20 PolySynth 146
EVOC 20 PolySynth formant lter
EVOC 20 PolySynth features two formant lter banks—one for the Analysis section and one
for the Synthesis section. Each bank provides up to 20 individual lters. The entire frequency
spectrum of an incoming signal is analyzed by the Analysis section and is divided equally into a
number of frequency bands. These analysis lter bands are mirrored by a corresponding number
of bands in the synthesis lter bank. Each lter bank controls the peak levels—the formants—
within these frequency bands.
The Formant Filter display is divided in two by a horizontal line. The upper half applies to the
Analysis section and the lower half to the Synthesis section. Parameter changes are instantly
reected in the Formant Filter display, thus providing invaluable feedback about what is
happening to the signal as it is routed through the two formant lter banks.
Formant Shift knob
Formant Stretch knob
Lowest button
Resonance knob
Highest button
High Frequency
parameters
Low Frequency
parameters
Formant lter parameters
•
Low and High Frequency parameters: Drag to set the lowest and highest frequencies allowed to
pass by the formant lter. Frequencies outside these boundaries are cut.
•
The length of the horizontal blue bar at the top represents the frequency range for both
analysis and synthesis (unless Formant Stretch or Formant Shift is used). You can move the
entire frequency range by dragging the blue bar. The silver handles on either end of the blue
bar set the Low Frequency and High Frequency values, respectively.
•
You can also drag vertically in the numeric elds to adjust the Low and High
frequency values.
•
Lowest and Highest buttons: Click to determine whether the lowest and highest lter bands act
as bandpass lters or whether they act as lowpass or highpass lters.
•
Lowest button: Determines whether the lowest lter band acts as a bandpass or highpass
lter. In bandpass mode, the frequencies above and below the lowest band are ignored. In
highpass mode, all frequencies below the lowest band are ltered.
•
Highest button: Determines whether the lowest lter band acts as a bandpass or lowpass
lter. In bandpass mode, the frequencies above and below the highest band are ignored. In
lowpass mode, all frequencies above the highest band are ltered.
•
Resonance knob: Rotate to determine the basic sonic character of the vocoder. Low settings
result in a softer character; high settings result in a sharper character. Technically, increasing
the Resonance value emphasizes the middle frequency of each frequency band.