Ian Andrews wrote:
Just an ignorant assumption, but would not the output of [noise~] itself
be generated from pseudo-random numbers? If not, then how does [noise~]
generate its randomness? Or is there something more complex at work?
Yes it's currently also a pseudo-random source. In fact it is this (from
d_osc.c):
static t_int *noise_perform(t_int *w)
{
t_sample *out = (t_sample *)(w[1]);
int *vp = (int *)(w[2]);
int n = (int)(w[3]);
int val = *vp;
while (n--)
{
*out++ = ((float)((val & 0x7fffffff) - 0x40000000)) *
(float)(1.0 / 0x40000000);
val = val * 435898247 + 382842987;
}
*vp = val;
return (w+4);
}
...which is a deterministic chaos generator.
But if you were to resample an oscillator that it's driving at a much
lower rate then you would get more entropy, so it seems more random, but
at the cost of losing a lot of samples.
Martin
Ian
On 05/07/2009, at 7:12 PM, Andrew Faraday wrote:
Just an idea, but if the hardware random number generators use a
jittery oscillator etc. Why not use [noise~] and [snapshot~] followed
by some arithmetic and [int] you could build what I assume would be
more random than the [random] box.
Andrew
> Date: Sun, 5 Jul 2009 00:22:51 -0400
> From: [email protected] <mailto:[email protected]>
> To: [email protected] <mailto:[email protected]>
> CC: [email protected] <mailto:[email protected]>; [email protected]
<mailto:[email protected]>
> Subject: Re: [PD] help_random/seed
>
> Mike Moser-Booth wrote:
> > IOhannes m zmölnig wrote:
> >> Frank Barknecht wrote:
> >>> Hallo,
> >>> cem guney hat gesagt: // cem guney wrote:
> >>>
> >>>> just started studying PD. going through the control examples i've
> >>>> been stuck trying to figure out the function of the message, seed
> >>>> 123 in the
> >>>> example for "random". not sure if i figured out the explanation below,
> >>>>
> >>>> Seeds are kept locally so that if two Randoms are seeded the same
> >>>> they will have the same output (or indeed you can seed the same one
> >>>> twice to repeat the output.)
> >>>
> >>> Yes, that's true, you understood correctly.
> >>>
> >>> Oh, wait, that's what's in the help-file! What exactly is cloudy there?
> >>
> >> probably the simple fact, that [random] despite of it's name does not
> >> really produce random numbers.
> >> mostly when computers present you a "random" number, then this number
> >> will only appear to be random, but in reality is just calculated as
> >> the next item of a totally deterministic series.
> >> (as a matter of fact, a new random number is usually generated by
> >> simple taking the last number and then applying some more or less
> >> complicated transformation on this number). this method is known as
> >> "pseudo random".
> >>
> >> you can set the "starting point" of the series by setting the "seed",
> >> which is the first number of the random sequence). since all [random]
> >> object use the same algorithm to calculate the next pseudo-random
> >> number, they will all end up with the same sequence if they all start
> >> with the same "seed".
> >> by default Pd uses different seeds for all [random] objects so they
> >> all appear to work independently.
> > In addition, it's probably worth mentioning that Pd will produce the
> > same seeds for each [random] every time you load the patch. So while
> > they appear to work independently, you will still get the same results
> > each time you first run a patch after loading it.
> >
>
> A lot of the latest cpus have hardware random number generators that
> work by having a jittery oscillator sample the cpu clock, or something
> along those lines. (Such a jittery oscillator is assumed to have
> normally distributed transition times.)
> It would be nice if the random source could be independently specified
> for all the pd objects that use random numbers, since the count of
> unreachable combinations when using the standard deterministic chaos
> generators is infinite.
>
> Martin
>
>
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