Sound: Filter (one formant)...

A command to filter every selected Sound object, with a single formant of a specified frequency and bandwidth.

## Algorithm

Two recursive filter coefficients are computed as follows:

p = −2 exp (−π bandwidth dt) cos (2π frequency dt)

q = exp (−2 i 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-place version: Sound: Filter with one formant (in-place)....