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Hi, i try to program a white noise generator with gaussian distribution. When i first used the rand() function i connected the 12-Bit DA-converter to a speaker. A periodic timer interrupt (about 400kHz) gets a rand number and puts it to the DA-converter.
I expected white noise, but wasn't satiesfied, i could hear a hum inside the white noise. The random numbers seemed to have some periodic pattern with a high repeat rate inside. I think with a spectrum-analyzer there would be some extra lines inside the spectrum. Now i wrote my own rand() function.
//*************************************************************************** int my_rand(int init_rand) { static unsigned int Z; if (init_rand) Z = init_rand; if (Z & 0x80000000) { Z<<=1; Z^=0x04C11DB7;//i saw it in a dream ;-) } else { Z<<=1; } return Z; } //***************************************************************************
After once beeing initialised with a value not zero it sounds great.
But is it mathematical correct?
After how many cycles does the initial value return?
Can i get a pseudo gaussian distribution with the following?
Z = my_rand(0); K = ((Z>>11 ^ Z>>22) & 0x3FF) +((Z>>11 ^ Z ) & 0x3FF) +((Z>>22 ^ Z>>5 ) & 0x3FF) +((Z ^ Z>>17) & 0x3FF); DAC0DAT = K<<16;//the 12bit-ADuC7026-DA-converter
There must be a more elegant method to have gaussian distribution!
Thanks for advice.