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Signal Modifiers: Standard Filters

tbvcf


  ar      tbvcf      asig, xfco, xres, kdist, kasym


Description

This opcode attempts to model some of the filter characteristics of a Roland TB303 voltage-controlled filter. Euler's method is used to approximate the system, rather than traditional filter methods. Cutoff frequency, Q, and distortion are all coupled. Empirical methods were used to try to unentwine, but frequency is only approximate as a result. Future fixes for some problems with this opcode may break existing orchestras relying on this version of tbvcf.

Performance

asig – input signal. Should be normalized to ±1.

xfco – filter cutoff frequency. Optimum range is 10,000 to 1500. Values below 1000 may cause problems.

xres – resonance or Q. Typically in the range 0 to 2.

kdist – amount of distortion. Typical value is 2. Changing kdist significantly from 2 may cause odd interaction with xfco and xres.

kasym – asymmetry of resonance. Typically in the range 0 to 1.

Example


;---------------------------------------------------------

; TBVCF Test

; Coded by Hans Mikelson December, 2000

;---------------------------------------------------------

  sr      =  44100   ; Sample rate

  kr      =  4410   ; Kontrol rate

  ksmps   =  10   ; Samples/Kontrol period

  nchnls  =  2        ; Normal stereo

  zakinit    50, 50



          instr 10



  idur    =          p3                                ; Duration

  iamp    =          p4                                ; Amplitude

  ifqc    =          cpspch(p5)                        ; Pitch to frequency

  ipanl   =          sqrt(p6)                          ; Pan left

  ipanr   =          sqrt(1-p6)                        ; Pan right

  iq      =          p7

  idist   =          p8

  iasym   =          p9



  kdclck  linseg     0, .002, 1, idur-.004, 1, .002, 0 ; Declick envelope



  kfco    expseg     10000, idur, 1000                 ; Frequency envelope



  ax      vco        1, ifqc, 2, 1                     ; Square wave

  ay      tbvcf      ax, kfco, iq, idist, iasym        ; TB-VCF

  ay      buthp      ay/1, 100                         ; Hi-pass



          outs       ay*iamp*ipanl*kdclck, ay*iamp*ipanr*kdclck

          endin



  f1 0 65536 10 1

  ; TeeBee Test

  ;   Sta  Dur  Amp    Pitch Pan  Q    Dist1 Asym

  i10 0    0.2  32767  7.00  .5   0.0  2.0   0.0

  i10 0.3  0.2  32767  7.00  .5   0.8  2.0   0.0

  i10 0.6  0.2  32767  7.00  .5   1.6  2.0   0.0

  i10 0.9  0.2  32767  7.00  .5   2.4  2.0   0.0

  i10 1.2  0.2  32767  7.00  .5   3.2  2.0   0.0

  i10 1.5  0.2  32767  7.00  .5   4.0  2.0   0.0

  i10 1.8  0.2  32767  7.00  .5   0.0  2.0   0.25

  i10 2.1  0.2  32767  7.00  .5   0.8  2.0   0.25

  i10 2.4  0.2  32767  7.00  .5   1.6  2.0   0.25

  i10 2.7  0.2  32767  7.00  .5   2.4  2.0   0.25

  i10 3.0  0.2  32767  7.00  .5   3.2  2.0   0.25

  i10 3.3  0.2  32767  7.00  .5   4.0  2.0   0.25

  i10 3.6  0.2  32767  7.00  .5   0.0  2.0   0.5

  i10 3.9  0.2  32767  7.00  .5   0.8  2.0   0.5

  i10 4.2  0.2  32767  7.00  .5   1.6  2.0   0.5

  i10 4.5  0.2  32767  7.00  .5   2.4  2.0   0.5

  i10 4.8  0.2  32767  7.00  .5   3.2  2.0   0.5

  i10 5.1  0.2  32767  7.00  .5   4.0  2.0   0.5

  i10 5.4  0.2  32767  7.00  .5   0.0  2.0   0.75

  i10 5.7  0.2  32767  7.00  .5   0.8  2.0   0.75

  i10 6.0  0.2  32767  7.00  .5   1.6  2.0   0.75

  i10 6.3  0.2  32767  7.00  .5   2.4  2.0   0.75

  i10 6.6  0.2  32767  7.00  .5   3.2  2.0   0.75

  i10 6.9  0.2  32767  7.00  .5   4.0  2.0   0.75

  i10 7.2  0.2  32767  7.00  .5   0.0  2.0   1.0

  i10 7.5  0.2  32767  7.00  .5   0.8  2.0   1.0

  i10 7.8  0.2  32767  7.00  .5   1.6  2.0   1.0

  i10 8.1  0.2  32767  7.00  .5   2.4  2.0   1.0

  i10 8.4  0.2  32767  7.00  .5   3.2  2.0   1.0

  i10 8.7  0.2  32767  7.00  .5   4.0  2.0   1.0

Author

Hans Mikelson
December, 2000 – January, 2001
New in Csound 4.10


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Signal Modifiers: Standard Filters