Description

Basic frequency modulated oscillator with linear interpolation.

Syntax

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

Initialization

ifn (optional) -- function table number. Requires a wrap-around guard point. Defaults to a sine wave/

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.

foscili differs from foscil in that the standard procedure of using a truncated phase as a sampling index is here replaced by a process that interpolates between two successive lookups. Interpolating generators will produce a noticeably cleaner output signal, but they may take as much as twice as long to run. Adequate accuracy can also be gained without the time cost of interpolation by using large stored function tables of 2K, 4K or 8K points if the space is available.

Examples

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

<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 foscili.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 foscili .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>

See Also

FM Synthesis

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