an open-source digital signal processing and sound synthesis language
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SHAPE -- input sound waveshaping instrument
in RTcmix/insts/jg


quick syntax:
SHAPE(outsk, insk, dur, AMP, MINDIST, MAXDIST, AMPNORMTABLE, inputchan, PAN, TRANSFERFUNC[, INDEXENV])

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.



   p0 = output start time (seconds)
   p1 = input start time (seconds)
   p2 = input duration (seconds)
   p3 = amplitude multiplier (relative multiplier of input signal)
   p4 = minimum distortion index (0.0-1.0)
   p5 = maximum distortion index (0.0-1.0)
   p6 = reference to an amplitude normalization table, or 0 for no normalization
   p7 = input channel
   p8 = pan (0-1 stereo; 0.5 is middle)
   p9 = reference to waveshaping tranfer function table
   p10 = index control envelope [optional; default is constant 1.0]

   p3 (amplitude), p4 (min index), p5 (max index), p8 (pan) and p10 (index)
   can receive dynamic updates from a table or real-time control source.

   p6 (amp normalization table) and p9 (transfer function) should be references to pfield table-handles.

   Author:  John Gibson, 3 Jan 2002; rev for v4, 7/21/04



SHAPE does a table-lookup waveshaping (distortion) on an arbitrary input soundfile. The WAVESHAPE instrument uses a similar approach, but does synthesis instead of signal-processing.

Usage Notes

SHAPE accepts input from a file, a real-time audio device, or from a bus. It also offers a different way of performing amplitude normalization than WAVESHAPE. SHAPE accomplishes this by applying a waveshaping transfer function to the input source. (See Dodge and Jerse, or any other computer music text, for a detailed explanation of this technique.)

For a short explanation of the waveshaping process and how to configure the transfer function (p8, "TRANSFERFUNCTION") along with the index control function (p9, "INDEXENV" if used) and index constraints (p3 and p4, "INDEXMIN", "INDEXMAX"), see the WAVESHAPE Usage Notes.

If you want to perform amplitude normalization, use a pfield table through p6 ("AMPNORMTABLE") with the normalization curve. Otherwise, set p6 to zero. The amplitude normalization control table allows you to decouple amplitude and timbral change, to some extent. (Read about this in the Roads "Computer Music Tutorial'' chapter on waveshaping.) The table maps incoming signal amplitudes, on the X axis, to amplitude multipliers, on the Y axis. The multipliers should be from 0 to 1. The amplitude multipliers are applied to the output signal, along with whatever overall amplitude curve is in effect. Generally, you'll want a curve that starts high and moves lower for the higher signal amplitudes. This will keep the bright and dark timbres more equal in amplitude. But anything is possible.

The output of SHAPE can be either stereo or mono.

Sample Scores

very basic:
   rtsetparams(44100, 2)
   load("WAVETABLE")
   load("SHAPE")

   bus_config("WAVETABLE", "aux 0 out")
   bus_config("SHAPE", "aux 0 in", "out 0-1")

   dur = 10
   amp = 10000
   freq = 200
   start = 0
   WAVETABLE(start, dur, amp, freq, 0)

   amp = 1.0
   ampenv = maketable("line", 1000, 0,0, 9,1, 10,0)

   transferfunc = maketable("cheby", "nonorm", 1000, 0.9, 0.3, -0.2, 0.6, -0.7, 0.9, -0.1)

   min = 0; max = 3.0
   indexguide = maketable("window", 1000, "hanning")    // bell curve

   SHAPE(start, inskip = 0, dur, amp*ampenv, min, max, 0, inchan=0, pan=0.5, transferfunc, indexguide)


slightly more advanced:
   rtsetparams(44100, 2)
   load("WAVETABLE")
   load("SHAPE")

   bus_config("WAVETABLE", "aux 0 out")
   bus_config("SHAPE", "aux 0 in", "out 0-1")

   dur = 20
   freq = 60

   amp = 20000
   wavet = maketable("wave", 2000, 1, .3, .1)
   WAVETABLE(start=0, dur, amp, freq, 0, wavet)

   transferfunc = maketable("wave", 1000, "square13")

   // sample-and-hold distortion index
   speed = 7   // sample-and-hold changes per second
   indexguide = makerandom("even", speed, min=0, max=1, seed=1)
   indexguide = makefilter(indexguide, "smooth", lag=20)
   minidx = 0.0
   maxidx = 3.0

   normfunc = maketable("curve", "nonorm", 1000, 0,1,-1, 1,.3)

   amp = 0.8
   env = maketable("line", 1000, 0,1, dur-.03,1, dur,0)

   SHAPE(start, inskip=0, dur, amp * env, minidx, maxidx, normfunc, 0, 1, transferfunc, indexguide)

   // vary distortion index for other channel
   indexguide = makerandom("even", speed, min=0, max=1, seed + 1)
   indexguide = makefilter(indexguide, "smooth", lag=20)
   SHAPE(start, inskip=0, dur, amp * env, minidx, maxidx, normfunc, 0, 0, transferfunc, indexguide)


See Also

maketable, makerandom, makefilter, DISTORT, SHAPE, DECIMATE, COMPLIMIT