Posted By
Bionic
on 2003-05-19
|  TED noise generator
In case you are curious about in the inner workings of the TED, this might be of interest for you:
Taking advantage of espresso, I managed to "guess" the noise generator circuit from a sample provided to me by Attila. The analysis showed, that the sample with just off by 3-4 bits.
The TED noise generator consists of an 8-Bit linear feedback shift register with taps on bit 7,5,4 and 1. One of the shift register bits is directly connected to voice output. An 8-Bit LFSR generates a pseudo random sequence with a period of 255. Due to the short period, the "randomness" of the signal is not very good and you get audible repetitions. This is not how you should design a noise generator...
Circuit and C-Code shown below.
Credits go to Levente for sampling the signal and to Attila Grósz for supplying it to me. Keep up the good work with YAPE!
Tim
----------------------------------------------------------------------
Circuit:
____ ____ ____ ____ ____ ____ ____ ____
| | | | | | | | | | | | | | | |
| 7 <|--| 6 <|--| 5 <|--| 4 <|--| 3 <|--| 2 <|--| 1 <|--| 0 <|--+--> OUT
|____| |____| |____| |____| |____| |____| |____| |____| |
| | | | ______ |
| | | |___| | |
| | |___________________________| | |
| |___________________________________| XNOR |o-+
|___________________________________________________| |
|______|
#include "stdio.h"
void main(void)
{
int im=1;
while (1)
{
im=(im<<1)+(1^((im>>7)&1)^((im>>5)&1)^((im>>4)&1)^((im>>1)&1));
printf("%i",(im&1)?'1':'0');
}
}
|
(I took the liberty of adding a <PRE> tag around the circuit to preserve the formatting.)
Unofrtunately there are a number of newly introduced bugs in 0.46 so I need fix it a little.
