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• Highest button: Click to determine whether the lowest filter band acts as a bandpass
or lowpass filter. In the Bandpass setting, the frequencies below the lowest bands
and above the highest bands are ignored. In the Lowpass setting, all frequencies
above the highest bands are filtered.
• Formant Stretch knob: Alters the width and distribution of all bands in the synthesis
filter bank. This can be a broader or narrower frequency range than that defined by
the Low and High Frequency parameters. See Using EVOC 20 PolySynth Formant Stretch
and Shift.
• Formant Shift knob: Moves all bands in the synthesis filter bank up or down the
frequency spectrum. See Using EVOC 20 PolySynth Formant Stretch and Shift.
• Resonance knob: Determines the basic sonic character of the vocoder. Low settings
result in a softer character; high settings result in a more snarling, sharper character.
Technically, increasing the Resonance value emphasizes the middle frequency of each
frequency band.
Using EVOC 20 PolySynth Formant Stretch and Shift
When Formant Stretch is set to 0, the width and distribution of the bands in the synthesis
filter bank at the bottom matches the width of the bands in the analysis filter bank at the
top. Low values narrow the width of each band in the synthesis filter bank, whereas high
values widen the bands. The control range is expressed as a ratio of the overall bandwidth.
When Formant Shift is set to 0, the positions of the bands in the synthesis filter bank
match the positions of the bands in the analysis filter bank. Positive values move the
synthesis filter bank bands up in frequency, whereas negative values move them down—in
respect to the analysis filter bank band positions.
When combined, Formant Stretch and Formant Shift alter the formant structure of the
resulting vocoder sound, which can lead to some interesting timbre changes. For example,
using speech signals and tuning Formant Shift up results in “Mickey Mouse” effects.
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/or the Formant Shift parameters can result in
the generation of unusual resonant frequencies, when high Resonance settings are used.
153Chapter 7 EVOC 20 PolySynth