MULTIFM()

MULTIFM

Configurable multi-oscillator FM synthesis instrument.

in RTcmix/insts/neil

quick syntax:

MULTIFM(outsk, dur, AMP, numosc, PAN, FREQ1, wavet1, … FREQN, wavetN, osc1, out1, index1, … oscN, outN, indexN)

CAPITALIZED parameters are pfield-enabled for table or dynamic control (see the maketable or makeconnection scorefile commands). Parameters after the [bracket] are optional and default to 0 unless otherwise noted.

Param Field	Parameter	Units	Dynamic	Optional	Notes
p0	output start time	-	no	no
p1	duration	-	no	no
p2	overall amplitude multiplier	-	yes	no
p3	number of oscillators	-	no	no
p4	pan	in percent-to-left format	yes	no
p5	oscillator 1 freq	Hz	yes	no	forms pair with next pfield
p6	oscillator 1 waveform	reference to pfield table-handle	no	no	forms pair with previous pfield

p5,p6, p7,p8, …, pN-1, pN form pairs of frequency / waveform values for each oscillator.

Param Field	Parameter	Units	Dynamic	Optional	Notes
pN-1	oscillator N/2 freq	Hz	yes	yes	forms pair with next pfield
pN	oscillator 1 waveform	reference to pfield table-handle	no	yes	forms pair with previous pfield

pO, pO+1, pO+2, … pP-2, pP-1, pP form triplets for oscillator connections in one of the two following forms:

Param Field	Parameter	Units	Dynamic	Optional	Notes
pO	oscillator pair number	1-N	no	no	1 refers to the 1st freq / waveform pair, p5-p6. 2 refers to the next pair, and so on
pO+1	where to direct the output of this oscillator	0	no	no	directs signal to audio output
pO+2	relative amplitude	linear multiple of p2	yes	no

or

Param Field	Parameter	Units	Dynamic	Optional	Notes
pO	oscillator pair number	1-N	no	no	1 refers to the 1st freq / waveform pair, p5-p6. 2 refers to the next pair, and so on
pO+1	where to direct the output of the indicated oscillator	1-N	no	no	direct it to modulate the frequency of the given oscillator
pO+2	modulation index	non-negative	yes	no

Parameters labled as Dynamic can receive dynamic updates from a table or real-time control source.

Any number of connections in any direction, including feedback, is acceptable.

Author: Neil Thornock (neilthornock at gmail), 11/12/16

MULTIFM is a complex (complicated) instrument that allows for the type of frequency (actually, phase) modulation made famous by the Yamaha DX7 and other such synthesizers. With this instrument, you can create a wildly complex FM instrument with any number of oscillators and any types of connections between them.

MULTIFM can produce mono or stereo output.

Usage Notes

If frequency modulation is new to you, it may be helpful to read up on it first and get familiar with basic terminology (carrier, modulator, index, etc.). See, for example, the documentation on FMINST.

p3 is the total number of oscillators used for this instrument. We can choose, say, to use three oscillators, Oscillators 1, 2, and 3. Beginning with p5, we will give a frequency/wavetable pair to each oscillator. p5 is the frequency for Oscillator 1, and p6 is its wavetable. p7 is the frequency for Oscillator 2, and p8 is its wavetable. p9 and p10 refer to Oscillator 3.

After the frequency/wavetable pairs, we specify their connections in sets of three numbers. For example, we can indicate connections as follows:

   1, 0, 1,
   2, 0, 0.5,
   2, 1, 5,
   3, 2, 4

Each triple specifies 1) which oscillator we are dealing with, 2) where to connect its output, and 3) its amplitude or index. Output can be 0 (referring to audio out) or another oscillator. In this case, Oscillator 1 sends its signal to audio out at a relative amplitude of 1. Oscillator 2 sends its signal to audio out also, but at half the amplitude of Oscillator 1. In the third line, Oscillator 2 modulates Oscillator 1 with an index of 5. In the fourth line, Oscillator 3 modulates Oscillator 2 with an index of 4.

Any kinds of connections are possible. Using five oscillators, we could specify connections as follows:

   1, 0, 1,
   2, 1, 3,
   3, 2, 4,
   3, 3, 1,
   4, 2, 5,
   5, 4, 3,
   5, 3, 3,
   2, 5, 1

Notice that an oscillator can feed back into itself or can feed back into an oscillator upstream.

Sample Score

   rtsetparams(44100, 2)
   load("MULTIFM")

   freq = 400
   wavet = maketable("wave", 1000, "sine")
   MULTIFM(0, 5, 10000, numosc=3, pan=0.5,
      freq, wavet,
      freq*2.01, wavet,
      freq*2.99, wavet,
      1, 0, 1,
      2, 1, 3,
      3, 2, 2
   )