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Chapter 6 Filter eects 133
EVOC 20 TrackOscillator formant lter
EVOC 20 TrackOscillator features two formant lter banks—one for the Analysis In section and
one for the Synthesis In section. The entire frequency spectrum of an incoming signal is analyzed
by the Analysis section and is divided equally into a number of frequency bands. Each lter bank
can control up to 20 of 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 reected in
the Formant Filter display, thus providing feedback on what is happening to the signal as it is
routed through the two formant lter banks.
Formant lter parameters
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Low and High Frequency parameters: Drag to determine the lowest and highest frequencies
allowed to pass by the lter section. Frequencies that fall outside these boundaries are cut.
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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.
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You can also drag in the numeric elds to adjust the frequency values separately.
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Lowest button: Click to switch the lowest lter band between bandpass or highpass lter
operation. In bandpass mode, the frequencies above and below the lowest band are ignored.
In highpass mode, all frequencies below the lowest band are ltered.
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Highest button: Click to switch the highest lter band between bandpass or lowpass lter
operation. In bandpass mode, the frequencies above and below the highest band are ignored.
In lowpass mode, all frequencies above the highest band are ltered.
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Formant Stretch knob: Rotate to change the width and distribution of all bands in the synthesis
lter bank. This can be a broader or narrower frequency range than that dened by the High
and Low Frequency parameters.
When Formant Stretch is set to 0, the width and distribution of the bands in the synthesis lter
bank at the bottom match the width of the bands in the analysis lter bank at the top. Low
values narrow the width of each band in the synthesis bank, whereas high values widen the
bands. The control range is expressed as a ratio of the overall bandwidth.
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Formant Shift knob: Rotate to move all bands in the synthesis lter bank up or down the
frequency spectrum.
When Formant Shift is set to 0, the positions of the bands in the synthesis lter bank match
the positions of the bands in the analysis lter bank. Positive values move the synthesis lter
bank bands up in frequency, whereas negative values move them down—in relation to the
analysis lter bank band positions.