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Re: white noise generation

by robert bristow-johnson <rbj@[EMAIL PROTECTED] > Jul 4, 2008 at 10:20 AM

On Jul 4, 9:48=A0am, Jerry Avins <j...@[EMAIL PROTECTED]
> wrote:
> esfield wrote:
> > The xor****ft generator I'm using has three xor operations and three
****=
ft
> > operations; which, if I understand correctly, are supposed to work
toge=
ther
> > to create a 32-bit random number. =A0
>
> > Here is the code (I'm doing an asm version of this):
> > unsigned long xor(){
> > static unsigned long y=3D2463534242; //seed
> > y^=3D(y<<13); y^=3D(y>>17); return (y^=3D(y<<5)); }

wow, i nearly can understand this, but not quite.  the ****ft-register
sequence operation i was thinking of is sorta described at

   http://www.dspguru.com/info/tutor/mls.htm

now maybe your operation above can be broken down into a normal
looking LFSR sequence, the operation would be (in C code)


static primitive_poly =3D 0x82D4E1B8;
static int state =3D 1;   // can be anything non-zero

int random_bit(void)
   {
   if (state&0x00000001)
      {
      state =3D (state>>1)^primitive_poly;
      }
    else
      {
      state =3D state>>1;
      }

   return state&0x00000001;
   }

an operation similar to that, is what i understand to be a
pseudorandom ****ft register sequence.  the LSB of "state" are bits
that are virtually white in their correlation (except for DC), but "
"state" itself, taken as a binary PCM value, does not make for a good,
white random number.


> > When you refer to the xor****ft method only producing one random bit at
=
a
> > time,
=2E..
> I didn't work through your code. There may be something clever that
> randomizes all the bits in the register, but I doubt it.

yeah, i'm skeptical too.  but i also hadn't worked through it.  maybe
these 3 ****ft and XOR operations can be shown to be equivalent to the
LFSR code above for a primitive polynomial that is somehow implied.
i'll have to look more closely after the holiday.

r b-j
 




 24 Posts in Topic:
white noise generation
"esfield" <e  2008-07-03 14:55:51 
Re: white noise generation
Piergiorgio Sartor <pi  2008-07-03 22:15:44 
Re: white noise generation
Paul Russell <prussell  2008-07-03 21:45:00 
Re: white noise generation
Jerry Avins <jya@[EMAI  2008-07-03 17:03:45 
Re: white noise generation
Piergiorgio Sartor <pi  2008-07-03 23:28:33 
Re: white noise generation
Jerry Avins <jya@[EMAI  2008-07-04 09:35:54 
Re: white noise generation
Piergiorgio Sartor <pi  2008-07-04 22:27:42 
Re: white noise generation
"SteveSmith" &l  2008-07-03 16:43:31 
Re: white noise generation
"ionic" <ion  2008-07-04 02:02:09 
Re: white noise generation
Ben Jackson <ben@[EMAI  2008-07-04 02:53:20 
Re: white noise generation
Jerry Avins <jya@[EMAI  2008-07-04 09:50:38 
Re: white noise generation
dbd <dbd@[EMAIL PROTEC  2008-07-03 16:15:19 
Re: white noise generation
robert bristow-johnson &l  2008-07-03 17:35:07 
Re: white noise generation
Piergiorgio Sartor <pi  2008-07-04 22:26:21 
Re: white noise generation
robert bristow-johnson &l  2008-07-03 17:51:13 
Re: white noise generation
"esfield" <e  2008-07-03 22:15:48 
Re: white noise generation
Jerry Avins <jya@[EMAI  2008-07-04 09:48:53 
Re: white noise generation
"SteveSmith" &l  2008-07-04 11:13:45 
Re: white noise generation
robert bristow-johnson &l  2008-07-04 10:20:51 
Re: white noise generation
robert bristow-johnson &l  2008-07-04 10:38:23 
Re: white noise generation
"SteveSmith" &l  2008-07-04 13:51:59 
Re: white noise generation
"John E. Hadstate&qu  2008-07-04 19:33:25 
Re: white noise generation
Jerry Avins <jya@[EMAI  2008-07-04 20:59:02 
Re: white noise generation
"John E. Hadstate&qu  2008-07-06 09:04:38 

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