10.6

316Logic Pro Instruments
Formant filter parameters
• Low/High Frequency parameters: Set the lowest and highest frequencies allowed to
pass by the formant filter. 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 fields to adjust the Low and High
frequency values.
• Lowest and Highest buttons: Click to determine whether the lowest and highest filter
bands act as bandpass filters or whether they act as lowpass or highpass filters.
• Lowest button: Determine whether the lowest filter band acts as a bandpass or
highpass filter. In bandpass mode, the frequencies above and below the lowest band
are ignored. In highpass mode, all frequencies below the lowest band are filtered.
• Highest button: Determine whether the lowest filter band acts as a bandpass or
lowpass filter. In bandpass mode, the frequencies above and below the highest band
are ignored. In lowpass mode, all frequencies above the highest band are filtered.
• Resonance knob: 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.
• Formant Stretch knob: Change 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.
• When Formant Stretch is set to 0, the width and distribution of the bands in the
synthesis filter bank match the width of the bands in the analysis filter bank. 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.
• Formant Shift knob: Move all bands in the synthesis filter bank up or down the
frequency spectrum.
• 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 interesting timbral 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 the Formant Shift parameters can result in the
generation of unusual resonant frequencies when high Resonance settings are used.