Is there any way to have a Normal-Derivation inside a Synth

CreCo · August 23, 2020, 11:55am

Hey Community,
I’m not abstinence of Super-Collider; But I have done very much of minor Projects with SuperCollider.
But new I’m having a tricky Problem with the creation of a SynthDef.
In a Synth-Project on my GitHub Page at IRCAM:

I need a from me so called Warmth Function.
This Function should realize the Deviation of Natural Instruments. In Because they ever sweep around the Parameters of a exact Physical Model of them. So this Deviation is commonly a Normal-Deviation.
My Problem is outside the Synth I would call easily anything like sum3rand.
But now I need this Distribution in a Synth.

So is there any Way Possibility or Workaround to achieve this.

Any Suggestions welcome

CreCo

jamshark70 · August 23, 2020, 1:26pm

First thing is to find exactly what sum3rand does (which took a little digging):

github.com

supercollider/supercollider/blob/develop/include/plugin_interface/SC_RGen.h#L206


      
          }
          
          /// Bilateral linearly distributed random float from -0.999 to +0.999.
          inline float RGen::fbilinrand() {
              float a = frand();
              float b = frand();
              return a - b;
          }
          
          /**
           * Generates a random float that is the
           * result of summing three uniform random generators to yield a
           * bell-like distribution.
           *
           * Larry Polansky's loose approximation of a gaussian generator.
           */
          inline float RGen::fsum3rand() { return (float)((frand() + frand() + frand() - 1.5) * 0.666666667); }
          
          /// Generate 32 bit integer from 0 to scale - 1
          inline int32 RGen::irand(int32 scale) { return (int32)floor(scale * drand()); }

(frand() + frand() + frand() - 1.5) * 0.666666667

frand() is 0 to 0.9999999…
So frand() + frand() + frand() may be as low as 0 and as high as (almost) 3.
- 1.5 shifts this range to +/- 1.5 (center at 0).
* 0.666667 pulls the range down to +/- 1.0.

So you can use the same formula with a server side random number UGen.

But actually a little easier because you can control the range of TRand, so it could be just:

var oneThird = 1/3, negThird = oneThird.neg;
var sum3rand = Array.fill(3, { TRand.kr(negThird, oneThird, trig) }).sum;

(Using variables to avoid repeating calculations.)

hjh

CreCo · August 23, 2020, 1:50pm

Very much Thanks,
this was the Solution I’m looking for.
It’s essay so I could use it for my Synth very powerful.

Thanks

CreCo