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resonr (Csound opcode)

A bandpass filter with variable frequency response.
ar      resonz      asig, kcf, kbw[, iscl, iskip]
kcf: center (cutoff) frequency
kbw: bandwith (frequency difference between the upper and the lower half points)
iskip: default 0. 0 will clear storage space.

Demonstration

This demonstration is similar to the one of the butterbp filter which produces almost the same output.
The following score on orchestra file can be used to show how reson filters frequncies. a440 is a signal that oscilates with 440 Hz. kfrq220_660 is the center frequency for reson and moves from 220 Hz up to 660 Hz. The filtered signal (afiltered) is sent to one channel while a440 is sent to the other channel. The filtered signal reaches the same amplitude as a440 after a second and is otherwise attenuated.
f1 0 2048 10 1

i1 0 2 
sr     = 44100
kr     = 4410
nchnls = 2

instr 1

  ilen = p3

  a440          oscili   10000, 440, 1
  kfrq220_660   line     220, ilen, 660
  afiltered     reson    a440, kfrq220_660, 110, 1

  outs          a440, afiltered
endin