crossfm — Two mutually frequency and/or phase modulated oscillators.
a1, a2 crossfm xfrq1, xfrq2, xndx1, xndx2, kcps, ifn1, ifn2 [, iphs1] [, iphs2]
a1, a2 crossfmi xfrq1, xfrq2, xndx1, xndx2, kcps, ifn1, ifn2 [, iphs1] [, iphs2]
a1, a2 crosspm xfrq1, xfrq2, xndx1, xndx2, kcps, ifn1, ifn2 [, iphs1] [, iphs2]
a1, a2 crosspmi xfrq1, xfrq2, xndx1, xndx2, kcps, ifn1, ifn2 [, iphs1] [, iphs2]
a1, a2 crossfmpm xfrq1, xfrq2, xndx1, xndx2, kcps, ifn1, ifn2 [, iphs1] [, iphs2]
a1, a2 crossfmpmi xfrq1, xfrq2, xndx1, xndx2, kcps, ifn1, ifn2 [, iphs1] [, iphs2]
ifn1 -- function table number for oscillator #1. Requires a wrap-around guard point.
ifn2 -- function table number for oscillator #2. Requires a wrap-around guard point.
iphs1 (optional, default=0) -- initial phase of waveform in table ifn1, expressed as a fraction of a cycle (0 to 1). A negative value will cause phase initialization to be skipped.
iphs2 (optional, default=0) -- initial phase of waveform in table ifn2, expressed as a fraction of a cycle (0 to 1). A negative value will cause phase initialization to be skipped.
xfrq1 -- a factor that, when multipled by the kcps parameter, gives the frequency of oscillator #1.
xfrq2 -- a factor that, when multipled by the kcps parameter, gives the frequency of oscillator #2.
xndx1 -- the index of the modulation of oscillator #2 by oscillator #1.
xndx2 -- the index of the modulation of oscillator #1 by oscillator #2.
kcps -- a common denominator, in cycles per second, for both oscillators frequencies.
crossfm implements a crossed frequency modulation algorithm. The audio-rate output of oscillator #1 is used to modulate the frequency input of oscillator #2 while the audio-rate output of oscillator #2 is used to modulate the frequency input of oscillator #1. This double feedback structure produces a rich set of sounds with some chaotic behaviour. crossfmi behaves like crossfm except that linear interpolation is used for table lookup.
crosspm and crosspmi implement cross phase modulation between two oscillators.
crossfmpm and crossfmpmi implement cross frequency/phase modulation between two oscillators. Oscillator #1 is frequency-modulated by oscillator #2 while oscillator #2 is phase-modulated by oscillator #1.
Warning | |
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Those opcodes may produce very rich spectra, especially with high modulation indexes, and in some cases foldover aliases may occur if the sampling rate is not high enough. Moreover the audio output may vary in function of the sampling rate, due to the non-linearity of the algorithm. In Csound, two other opcodes have this characteristic: planet and chuap. |
Here is an example of the crossfm opcode. It uses the file crossfm.csd.
Example 191. Example of the crossfm opcode.
<CsoundSynthesizer> <CsOptions> -d -o dac </CsOptions> <CsInstruments> sr = 48000 ksmps = 10 nchnls = 2 0dbfs = 1 instr 1 idur = p3 iamp = p4 ifrq1 = p5 ifrq2 = p6 indx1 = p7 indx2 = p8 kenv linen iamp, 0.05, idur, 0.2 a1, a2 crossfm ifrq1, ifrq2, indx1, indx2, 1, 1, 1 outs a1*kenv, a2*kenv endin instr 2 kx init 0.0 kdx init 0.1 kdur init p4 kamp init p5 kndx init 0 kmax init p6 kfq1 init 440.0 kfq2 init 557.0 knx1 init 3.5 knx2 init 4.8 event "i", 1, kx, kdur, kamp, kfq1, kfq2, knx1, knx2 kx = kx + kdx knx1 = knx1 - 0.025 knx2 = knx2 - 0.075 kndx = kndx + 1 if (kndx <= kmax) kgoto nextone turnoff nextone: endin </CsInstruments> <CsScore> f 1 0 16384 10 1 0 i 2 0 2 0.67 0.16 150 i 1 15.1 1.5 0.1 440 557 -0.25 -6.45 0.05 1.2 e </CsScore> </CsoundSynthesizer>
More information about frequency modulation on Wikipedia: http://en.wikipedia.org/wiki/Frequency_modulation_synthesis
More information on these opcodes: http://www.csoundjournal.com/issue12/crossfm.html.