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Signal Generators: Granular Synthesis

grain2, grain3

  ar      grain2     kcps, kfmd, kgdur, iovrlp, kfn, iwfn[, irpow[, iseed[, imode]]]
  ar      grain3     kcps, kphs, kfmd, kpmd, kgdur, kdens, imaxovr, kfn, iwfn, kfrpow, kprpow[, iseed[, imode]]

Description

Generate granular synthesis textures. grain2 is simpler to use, but grain3 offers more control.

Initialization

iovrlp – fixed number of overlapping grains in grain2

imaxovr – maximum number of overlapping grains in grain3. The number of overlaps can be calculated as kdens*kgdur, however, imaxovr can be overestimated at no cost in rendering time. A single overlap uses 16 to 32 bytes of memory, depending on operating system.

iwfn – function table containing window waveform. Use GEN20 to calculate iwfn.

irpow – controls the random distribution of grain frequency. If irpow is positive, the distribution (where x is in the range -1 to 1) is:
  abs(x)(1/irpow)-1

For negative irpow values, the distribution is:
  (1 - abs(x))(-1/irpow)-1

Setting irpow to -1, 0, or 1 will result in uniform distribution. This is also faster to calculate. The default value of irpow is 0.

iseed – seed value for the random number generator. iseed must be a positive integer in the range 1 to 2147483646 (231 - 2). The default is 0.

imode – sum of the following values (default is 0):

Performance

kcps – grain frequency in Hz

kphs – grain phase

kfmd – bipolar random variation of grain frequency, in Hz

kpmd – bipolar random variation of beginning phase

kgdur – grain duration in seconds. kgdur also controls the duration of already active grains, by controlling the speed at which iwfn is read. This is unaffected by imode.

kdens – number of grains per second. In grain2, kdens = iovrlp/kgdur.

kfrpow – distribution of random frequency variation. See irpow.

kprpow – distribution of random phase variation. See irpow.

kfn – function table containing the grain waveform. Aliasing can be avoided by selecting, at k-rate, from a set of band-limited tables generated by GEN30.

grain3 will emulate grain2 by setting kphs = 0.5, kpmd = 0.5, and kprpow = 0.

grain2 Random Distribution
Figure 1: grain2 Random Distribution

Author

Istvan Varga
2001
New Csound 4.16


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Signal Generators: Granular Synthesis