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Chapter 8 EVOC 20 PolySynth 147
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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 Low
and High Frequency parameters.
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When Formant Stretch is set to 0, the width and distribution of the bands in the synthesis
lter bank match the width of the bands in the analysis lter bank. Low values narrow the
width of each band in the synthesis lter 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.
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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 respect to the
analysis lter bank band positions.
When combined, Formant Stretch and Formant Shift alter the formant structure of the resulting
vocoder sound, which can lead to interesting timbral changes. For example, using speech signals
and tuning Formant Shift up results in “Mickey Mouse” eects.
Formant Stretch and Formant Shift are also useful if the frequency spectrum of the synthesis
signal does not complement the frequency spectrum of the analysis signal. You could create a
synthesis signal in the high-frequency range from an analysis signal that mainly modulates the
sound in a lower-frequency range, for example.
Note: The use of the Formant Stretch and the Formant Shift parameters can result in the
generation of unusual resonant frequencies when high Resonance settings are used.