foscil
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## foscil

foscil — A basic frequency modulated oscillator.

## Description

A basic frequency modulated oscillator.

## Syntax

    ares foscil xamp, kcps, xcar, xmod, kndx, ifn [, iphs]

## Initialization

ifn -- function table number. Requires a wrap-around guard point.

iphs (optional, default=0) -- initial phase of waveform in table ifn, expressed as a fraction of a cycle (0 to 1). A negative value will cause phase initialization to be skipped. The default value is 0.

## Performance

xamp -- the amplitude of the output signal.

kcps -- a common denominator, in cycles per second, for the carrier and modulating frequencies.

xcar -- a factor that, when multiplied by the kcps parameter, gives the carrier frequency.

xmod -- a factor that, when multiplied by the kcps parameter, gives the modulating frequency.

kndx -- the modulation index.

foscil is a composite unit that effectively banks two oscil opcodes in the familiar Chowning FM setup, wherein the audio-rate output of one generator is used to modulate the frequency input of another (the “carrier”). Effective carrier frequency = kcps * xcar, and modulating frequency = kcps * xmod. For integral values of xcar and xmod, the perceived fundamental will be the minimum positive value of kcps * (xcar -- n * xmod), n = 1,1,2,... The input kndx is the index of modulation (usually time-varying and ranging 0 to 4 or so) which determines the spread of acoustic energy over the partial positions given by n = 0,1,2,.., etc. ifn should point to a stored sine wave. Previous to version 3.50, xcar and xmod could be k-rate only.

## Examples

Here is an example of the foscil opcode. It uses the files foscil.orc and foscil.sco.

Example 155. Example of the foscil opcode.

    /* foscil.orc */
    ; Initialize the global variables.
    sr = 44100
    kr = 4410
    ksmps = 10
    nchnls = 1

    ; Instrument #1 - a basic FM waveform.
    instr 1
      kamp = 10000
      kcps = 440
      kcar = 600
      kmod = 210
      kndx = 2
      ifn = 1

      a1 foscil kamp, kcps, kcar, kmod, kndx, ifn
      out a1
    endin
    /* foscil.orc */

    /* foscil.sco */
    ; Table #1, a sine wave.
    f 1 0 16384 10 1

    ; Play Instrument #1 for 2 seconds.
    i 1 0 2
    e
    /* foscil.sco */

## Credits

Example written by Kevin Conder.

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