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 158. 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 ; Audio out Audio in No messages -odac -iadc -d ;;;RT audio I/O ; For Non-realtime ouput leave only the line below: ; -o foscil.wav -W ;;; for file output any platform </CsOptions> <CsInstruments> ; 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 </CsInstruments> <CsScore> ; Table #1, a sine wave. f 1 0 16384 10 1 ; Play Instrument #1 for 2 seconds. i 1 0 2 e </CsScore> </CsoundSynthesizer>