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A command to filter every selected Sound object, with a single formant of a specified frequency and bandwidth.
Two recursive filter coefficients are computed as follows:
| p = –2 exp (–π bandwidth dt) cos (2π frequency dt) |
| q = exp (–2π bandwidth dt) |
where dt is the sample period. The new signal y is then computed from the old signal x and itself as
| y1 := x1 |
| y2 := x2 – p y1 |
| ∀n ≥ 3: yn := xn – p yn-1 – q yn-2 |
After filtering, the sound y is scaled so that its absolute extremum is 0.9.
For a comparative discussion of various filtering methods, see the Filtering tutorial.
This filter has an in-line version: Sound: Filter with one formant (in-line)....
© ppgb, March 9, 2003