These controls are identical across all engines and also available in the DynFilter effect.
Category Filter category: Analog, Formant or State Variable (StateVar)
St. Filter stages (1 to 5)
Filter Type or Edit This depends on the selected filter category. For Analog and StateVar various filters can be selected. For Formant a window enabling you to graphically edit the formants is opened
C.freq/BS.pos Centre Frequency for Analog and StateVar. Base position of the vowel sequence for Formant
Q Q factor for the filter
V.Sns. Velocity sensing. How much the filter is influenced by (MIDI) velocity of the note
VF.Sns. Velocity sensing function i.e the curve it follows.
Gain Filter output gain
Freq.tr. Amount of frequency tracking for the filter. If this is positive (rightmost) higher note frequencies will shift the filter cutoff frequency higher. Default range is -100% to 98.4% unless the checkbox above ('- / +') is selected: in this case the range is 0% to 198.4%
The Formant Filter
When the formant window is selected, the FilterType list is replaced by an Edit button, and clicking on this opens the window shown. These controls are additional to the others and adjust individual formants and the vowels they are contained in. Also, remember that the formant filter interacts with the filter envelope.
There are six vowels each with 12 formants, although you can chose to use only 2 or 3 of these.
For a deep understanding of formant filtering there is a highly detailed Wikipedia article Here.
Formants The number of active formants.
Fr.Sl (formant slowness) The rate at which one vowel morphs to the next.
Vw.Cl (vowel clearness) The amount of overlap when vowels transition.
Vowel no. The vowel being edited. If you are editing one that isn't in the current sequence it will have a redish background.
Formant The formant being edited.
Freq The frequency of the current formant. Uniquely this has no default value. From Yoshimi V2.3.0 there is a pseudo default.
Q The current formant's Q factor.
Amp The amplitude of the current formant.
Seq.Size (sequence size) The number of active vowels.
S.Pos. (sequence position) The order of the vowels.
Vowel The vowel number at the sequence position shown.
Stretch Changes the time and width of lower frequency formants relative to higher ones.
Neg.Input Inverts the input from the Envelope and/or LFO.
C.f. (centre frequency) The centre point of the complete filter.
Oct. (octaves) The pitch range of the complete filter.
Note
Although the sequence size sets the number of active vowels it doesn't determine which ones can be selected for any sequence position. If you have three vowels active (the default) you could have vowels 6, 3, 4 at positions 1, 2, 3 respectively.
The Formant Graph
You can control some of the parameters by placing the mouse pointer over the yellow lines representing each formant. While making changes, the respective controls will move accordingly.
Holding down either left or right mouse buttons and moving the mouse sideways will change the formant's center frequency.
Moving vertically while holding down the left button will change the amplitude. Alternatively holding down the right button changes the formant's Q factor.
Anywhere on the graph, the scroll-wheel changes the octave range, and holding Shift at the same time changes the center frequency.
If your mouse has extra buttons on the sides (many haven't) these can be used to switch between the formants instead of moving the mouse across to the next one.
This is especially useful for controlling most of the formant features one-handed, quickly, while also playing on a keyboard.
The Formant Pseudo Default
When a formant filter is first created the frequency control for each of the individual formants will be set randomly. However, with Yoshimi versions V2.3.0 and later, this setting becomes a pseudo default and the knob pointer colour will behave accordingly.
An extra wrinkle is that if this has been changed and the instrument is then saved, the saved copy will have the current value marked as the default, without affecting the running version.
Also, keep in mind that a reset, or switching to a different filter type always clears all filter settings and the formant frequency controls will gain new random values.
