bpf
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## bpf

bpf — Break point function with linear interpolation

## Description

Plugin opcode in emugens.

Break-point function with linear interpolation.

## Syntax

    ky bpf kx, kx1, ky1, kx2, ..., kxn, kyn

    iy bpf ix, ix1, iy1, ix2, ..., ixn, iyn

    kys[] bpf kxs[], kx1, ky1, kx2, ..., kxn, kyn

    iys[] bpf ixs[], ix1, iy1, ix2, ..., ixn, iyn

    ky bpf kx, kxs[], kys[]

    iy bpf ix, ixs[], iys[]

    ay bpf ax, kx1, ky1, kx2, ..., kxn, kyn

    ay bpf ax, kxs[], kys[]

    ky, kw bpf kx, kxs[], kys[], kws[]

## Performance

kx -- Input value

kxn, kyn -- Defines a breakpoint. Can be changed at krate, but all kxs must be sorted

The points (kx1, ky1), (kx2, ky2), etc, define a linearly interpolated function. This function is evaluated at point kx. This function extends to both -inf and +inf, so if kx < kx1 then ky = ky1 and the same holds true the other end.

These are equivalent:

          ky bpf kx, 0, 0,  0.5, 10,  1.02, 200

          itab ftgenonce 0, 0, -27, 0, 0, 50, 10, 102, 200
          ky = tablei(limit(kx, 0, 1.02)*100, itab)

| Note
x values need to be sorted. Both x and y values can change but x values must stay sorted.

## Examples

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

Example 107. Example of the bpf opcode.

    <CsoundSynthesizer>
    <CsOptions>
    -odac
    </CsOptions>
    <CsInstruments>

    ; Example for opcode bpf

    /*

      bpf stands for Break Point Function

      Given an x value and a series of pairs (x, y), it returns
      the corresponding y value in the linear curve defined by the
      pairs

      It works both at i- and k- time

      ky    bpf kx,    kx0, ky0, kx1, ky1, kx2, ky2, ...
      kys[] bpf kxs[], kx0, ky0, kx1, ky1, kx2, ky2, ...

      NB: x values must be ordered (kx0 < kx1 < kx2 etc)

      See also: bpfcos, linlin, lincos

    */

    sr = 44100
    ksmps = 64
    nchnls = 2
    0dbfs = 1

    instr 1
      kx line -1, p3, 2.5
      ky bpf kx,        \
             0,    0,   \
             1.01, 10,  \
             2,    0.5, \
             2.5,  -1
      if metro(10) == 1 then
        printsk "kx: %f   ky: %f \n", kx, ky
      endif
    endin

    instr 2
      ; test i-time
      ix = 1.2
      iy bpf ix, 0,0, 0.5,5, 1,10, 1.5,15, 2,20, 2.5,25, 3,30
      prints "iy: %f", iy
      turnoff
    endin

    instr 3
      ; bpf also works with arrays
      kx[] fillarray 0, 0.15, 0.25, 0.35, 0.45, 0.55, 0.6
      ky[] bpf kx, 0,0, 0.1,10, 0.2,20, 0.3,30, 0.4,40, 0.5,50
      printarray ky, 1, "", "ky="
      turnoff
    endin

    instr 4
      ; bpf as an envelope generator, like linsegb but driven by external phase
      ; bpf + rms can also be used as compressor

      atime linseg 0, p3*0.62, p3, p3*0.38, 0
      aenv = bpf(atime, 0,0, 0.1,1, 0.5, 0.2) ^ 2
      kbw  = bpf(timeinsts(), 0, 0, p3*0.62, 1) ^ 3
      asig = (beosc(1000, kbw, -1, rnd(6.28)) + beosc(1012, kbw, -1, rnd(6.28))) * 0.3
      kratio bpf dbamp(rms:k(asig)), -12, 1, -6, 0.4, -3, 1/100
      asig *= aenv * interp(lagud(kratio, 0.01, 0.1))
      outs asig, asig
    endin

    </CsInstruments>
    <CsScore>
    ; i 1 0 3
    ; i 2 0 -1
    ; i 3 0 -1
    i 4 0 3

    </CsScore>
    </CsoundSynthesizer>

## See also

Linear and Exponential Generators

## Credits

By: Eduardo Moguillansky 2017

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