4 ms·

With a linear feedback shift register, the input is the XOR of some stage outputs. (XOR is linear when considered mathematically since it's basically bitwise ad

by kens 10y ago

With a linear feedback shift register, the input is the XOR of some stage outputs. (XOR is linear when considered mathematically since it's basically bitwise addition.) If you use other logic functions, then it's nonlinear. The 76477 uses a combination of XOR and NAND, making it nonlinear. The disadvantage of a linear feedback shift register is it can get stuck at all zeros. But the 76477's shift register gets set by the inhibit line, so it couldn't get stuck. So I really don't know why they used a nonlinear circuit. As far as I can tell, it just makes the performance worse.

Cyph0n 10y ago
I see, that's pretty interesting. They could have gotten a much better period had they just used a standard primitive polynomial for a 32-bit LFSR.
- db48x 10y ago
  This isn't crypyography; probably the listener won't notice the difference.
  - Cyph0n 10y ago
    What I'm talking about would need almost zero extra work.
    - deleted 10y ago
      [deleted]
- colanderman 10y ago
  They could have made the chip a lot smaller (= cheaper to produce). For the period they actually achieved, they could have gotten away with a 16-bit LFSR, requiring half the die area for that function (which looks like it was quite significant).
  - crb3 10y ago
    16 isn't a good size according to the Rosenberg paper (http://www.cs.miami.edu/~burt/learning/Csc609.022/random_numbers.html http://www.cs.miami.edu/~burt/learning/Csc609.022/random_num...) but 15 and 17 are sizes you could program an ATtiny45 to generate if you just wanted that quality of noise. I'm going to be real interested in trying out the actual noise-generator logic in the follow-up article to see if I can hear any useful tonal difference. Maybe they were just frustrated by hardware that kept drifting into the forbidden state and brute-forced it until it couldn't; I've had that happen with PRNGs I built with series-4000 CMOS logic and xgates. Stay tuned, I guess.
deleted 10y ago
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by kens 10y ago

Cyph0n 10y ago

I see, that's pretty interesting. They could have gotten a much better period had they just used a standard primitive polynomial for a 32-bit LFSR.

db48x 10y ago
This isn't crypyography; probably the listener won't notice the difference.
- Cyph0n 10y ago
  What I'm talking about would need almost zero extra work.
  - deleted 10y ago
    [deleted]
colanderman 10y ago
They could have made the chip a lot smaller (= cheaper to produce). For the period they actually achieved, they could have gotten away with a 16-bit LFSR, requiring half the die area for that function (which looks like it was quite significant).
- crb3 10y ago
  16 isn't a good size according to the Rosenberg paper (http://www.cs.miami.edu/~burt/learning/Csc609.022/random_numbers.html http://www.cs.miami.edu/~burt/learning/Csc609.022/random_num...) but 15 and 17 are sizes you could program an ATtiny45 to generate if you just wanted that quality of noise. I'm going to be real interested in trying out the actual noise-generator logic in the follow-up article to see if I can hear any useful tonal difference. Maybe they were just frustrated by hardware that kept drifting into the forbidden state and brute-forced it until it couldn't; I've had that happen with PRNGs I built with series-4000 CMOS logic and xgates. Stay tuned, I guess.

deleted 10y ago

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