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 Forum index » Clavia Nord Modular » G2 Building Blocks
Linear Feedback Shift Register - pseudo random generator
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Blue Hell
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PostPosted: Sat Jan 19, 2008 12:26 pm    Post subject: Linear Feedback Shift Register - pseudo random generator Reply with quote  Mark this post and the followings unread

A linear Feedback Shift Register, as used for pseudo random generators.

See : Wikipedia

It has a table of various polynomials, I implemented the last one as an example. Just past the last one is a link to a PDF on the Xilinx website having many more.

In this patch I took the shift register outputs and combined them in a Klee like manner to do linear frequency control on a sine oscillator. Sounds a bit like the bleeps that used to be at one end of the FM radio.

I used XNOR ports instead of XOR ports to make the sequence self starting.


l_f_s_r.pch2
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Linear Feedback Shift Register - pseudo random generator

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 Filename:  l_f_s_r.pch2
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JLS



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PostPosted: Sun Jan 20, 2008 2:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks
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iPassenger



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PostPosted: Mon Jan 21, 2008 11:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Loved the idea Blue (Thanks), so thought i would make one of my own.

::>>

http://www.electro-music.com/forum/post-164678.html#164678

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dorremifasol



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PostPosted: Fri Jan 25, 2008 6:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Great patch!

I always wanted to simulate the LFSR noise sound of the Game Boy in the G2, but I'm not a good G2 patcher yet... I have emulated it in software, though... in my GB emulator.

The GB has a switchable LFSR of 7 and 15 stages, giving 128 or 32768 random values before repeating. I might try to convert your patch to suit this behavior... but first I will need to understand it!

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Blue Hell
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PostPosted: Fri Jan 25, 2008 12:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

When you have questions I'll try to answer them Very Happy
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also .. could someone please turn down the thermostat a bit.
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JohnL



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PostPosted: Sun Apr 05, 2009 9:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have played around with Blue Hell's patch to make it sound a bit more musical (to my ears, at least), and the concept is just amazing. Between the LFSR-generated patterns and the strange way the Klee-like programming generates the notes, and the canon created by the delay, the right combination of mixer pot positions results in a kind of fractal self-similarity of ever-changing patterns. I've had the thing running all day, and it's hardly even much of a noodle. I can see I'm going to spend I while exploring this!

But I have a question. I read up on the background (thanks for the reference links!), and I think I understand how the thing works (after going through one round of filling the shift register on paper!). But am I right that what you have programmed is not the polynomial x19 + x18 + x17 + x14 + 1 (I don't know how to do superscript here), but it's mirror image complement x19 + x5 + x2 + x + 1? This would give the inversion of the first sequence. Or does substituting XNORs for XORs reverse the sequence again? Now that I think about it, it would. So I guess it is just a naming convention which polynomial you call it.

Thanks for a wonderful patch!
John
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JohnL



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PostPosted: Sun Apr 05, 2009 9:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oops! My modified patch is at:
http://electro-music.com/forum/topic-33466.html

J
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cappy2112



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PostPosted: Sun May 03, 2009 9:25 pm    Post subject: Re: Linear Feedback Shift Register - pseudo random generator Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
A linear Feedback Shift Register, as used for pseudo random generators.


And it's demo-friendly

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