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):

• 64: synchronize beginning phase of grains to kcps. Applicable to grain3 only.
• 32: start all grains at integer sample location. While this may be faster in some cases, it makes the timing of the grain envelopes less accurate. Applicable to grain3 only.
• 16: do not render grains with a start time less than zero. Applicable to grain3 only.
• 8: interpolate window waveform (slower)
• 4: do not interpolate grain waveform (faster, but lower quality)
• 2: grain frequency is continuously modified by kcps and kfmd. By default, each grain keeps the frequency with which it was launched. This may be slower at high control rates. In grain3 this option also controls phase modulation (kphs).
• 1: skip initialization

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.

Figure 1: grain2 Random Distribution

Author

Istvan Varga
2001
New Csound 4.16