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tbvcf

Models 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.

Syntax

ares = tbvcf(asig, xfco, xres, kdist, kasym [, iskip])

ares tbvcf asig, xfco, xres, kdist, kasym [, iskip]

Initialization

iskip (optional, default=0) -- if non zero skip the initialisation of the filter. (New in Csound version 4.23f13 and 5.0)

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.

Examples

Here is an example of the tbvcf opcode. It uses the file tbvcf.csd.

Example of the tbvcf opcode.
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<CsoundSynthesizer>
<CsOptions>
; Select audio/midi flags here according to platform
; Audio out   Audio in    No messages
-odac           -iadc     -d     ;;;RT audio I/O
; For Non-realtime ouput leave only the line below:
; -o tbvcf.wav -W ;;; for file output any platform
</CsOptions>
<CsInstruments>

;---------------------------------------------------------
; TBVCF Test
; Coded by Hans Mikelson December, 2000
;---------------------------------------------------------
  sr =  44100   ; Sample rate
  ksmps =  10   ; Samples/Kontrol period
  nchnls =  2        ; Normal stereo
  0dbfs = 1


          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, 0.9, idur-.004, 0.9, .002, 0   ; Declick envelope
kfco            expseg  10000, idur, 1000                       ; Frequency envelope
ax              vco             1, ifqc, 2, 0.5                 ; 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


</CsInstruments>
<CsScore>

f1 0 65536 10 1

; TeeBee Test
;   Sta  Dur  Amp    Pitch Pan  Q    Dist1 Asym
i10 0    0.2  0.5    7.00  .5   0.0  2.0   0.0
i10 0.3  0.2  0.5    7.00  .5   0.8  2.0   0.0
i10 0.6  0.2  0.5    7.00  .5   1.6  2.0   0.0
i10 0.9  0.2  0.5    7.00  .5   1.7  2.0   0.0
i10 1.2  0.2  0.5    7.00  .5   1.8  2.0   0.0
i10 1.8  0.2  0.5    7.00  .5   0.0  2.0   0.25
i10 2.1  0.2  0.5    7.00  .5   0.8  2.0   0.25
i10 2.4  0.2  0.5    7.00  .5   1.6  2.0   0.25
i10 2.7  0.2  0.5    7.00  .5   1.8  2.0   0.25
i10 3.0  0.2  0.5    7.00  .5   1.9  2.0   0.25
i10 3.3  0.2  0.5    7.00  .5   2.0  2.0   0.25
i10 3.6  0.2  0.5    7.00  .5   0.0  2.0   0.5
i10 3.9  0.2  0.5    7.00  .5   0.8  2.0   0.5
i10 4.2  0.2  0.5    7.00  .5   1.6  2.0   0.5
i10 4.5  0.2  0.5    7.00  .5   1.8  2.0   0.5
i10 4.8  0.2  0.5    7.00  .5   1.9  2.0   0.5
i10 5.1  0.2  0.5    7.00  .5   2.0  2.0   0.5
i10 5.4  0.2  0.5    7.00  .5   0.0  2.0   0.75
i10 5.7  0.2  0.5    7.00  .5   0.8  2.0   0.75
i10 6.0  0.2  0.5    7.00  .5   1.6  2.0   0.75
i10 6.3  0.2  0.5    7.00  .5   1.8  2.0   0.75
i10 6.6  0.2  0.5    7.00  .5   1.9  2.0   0.75
i10 6.9  0.2  0.5    7.00  .5   2.0  2.0   0.75
i10 7.2  0.2  0.5    7.00  .5   0.0  2.0   1.0
i10 7.5  0.2  0.5    7.00  .5   0.8  2.0   1.0
i10 7.8  0.2  0.5    7.00  .5   1.6  2.0   1.0
i10 8.1  0.2  0.5    7.00  .5   1.8  2.0   1.0
i10 8.4  0.2  0.5    7.00  .5   1.9  2.0   1.0
i10 8.7  0.2  0.5    7.00  .5   2.0  2.0   1.0
e


</CsScore>
</CsoundSynthesizer>

See also

Standard Filters: Resonant Low-pass filters

Credits

Author: Hans Mikelson
December, 2000 -- January, 2001

New in Csound 4.10