
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
y_{1} := x_{1} 
y_{2} := x_{2} – p y_{1} 
∀n ≥ 3: y_{n} := x_{n} – p y_{n1} – q y_{n2} 
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 inplace version: Sound: Filter with one formant (inplace)....
© ppgb, March 9, 2003