foscil — A basic frequency modulated oscillator.

*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.

*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* = 0,1,2,... 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.

The actual formula used for this implementation of FM synthesis
is
*xamp* * cos(2π * *t* * *kcps* *
*xcar* +
*kndx* * sin(2π * *t ** *kcps* *
*xmod*) - π),
assuming that the table is a sine wave.

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

**Example 368. Example of the foscil opcode.**

See the sections *Real-time Audio* and *Command Line Flags* for more information on using command line flags.

<CsoundSynthesizer> <CsOptions> ; Select audio/midi flags here according to platform -odac ;;;realtime audio out ;-iadc ;;;uncomment -iadc if realtime audio input is needed too ; For Non-realtime ouput leave only the line below: ; -o foscil.wav -W ;;; for file output any platform </CsOptions> <CsInstruments> sr = 44100 ksmps = 32 nchnls = 2 0dbfs = 1 instr 1 kcps = 440 kcar = 1 kmod = p4 kndx line 0, p3, 20 ;intensivy sidebands asig foscil .5, kcps, kcar, kmod, kndx, 1 outs asig, asig endin </CsInstruments> <CsScore> ; sine f 1 0 16384 10 1 i 1 0 9 .01 ;vibrato i 1 10 . 1 i 1 20 . 1.414 ;gong-ish i 1 30 5 2.05 ;with "beat" e </CsScore> </CsoundSynthesizer>

More information about frequency modulation on Wikipedia: *http://en.wikipedia.org/wiki/Frequency_modulation_synthesis*