[sdiy] Uniformly distributed noise generator?

Scott Gravenhorst music.maker at gte.net
Mon Jun 10 15:15:54 CEST 2013


Tom Wiltshire <tom at electricdruid.net> wrote:
>Hi Damian,
>
>On 10 Jun 2013, at 12:37, "cheater00 ." <cheater00 at gmail.com> wrote:
>
>> - analog noise is truly random, not pseudo-random
>
>In theory. In practice, analog noise is unlikely to be totally 
>pure, and a good digital implementation would give better 
>quality. 

I agree with Tom.

It has been sooo long since the implementation of the chuff chuff LFSR with only a
few bits and low clock rate that it is truly a ridiculous comparison to analog noise
(and no, Damian, I am not saying you made that comparison).  32 bit LFSR noise is
clean and smooth enough IMO, but 64 bits is like silk and is easy to do and with the
clock rates that modern (and inexpensive) MCUs or FPGAs use, it won't repeat in any
musical session you do unless you want it to.  It might not repeat in your
lifetime...  And then, look at 128 bit LFSRs.

Coding an LFSR is hardly a brain twister.  Pseudo code at least is available, if not
the exact code for your favorite MCU.  But even if you have to bang it out yourself,
it's a worthwhile exercise.

It's always been for me the ear that is the final decider.  If you can hear "bad" in
a modern, long LFSR digital noise generator, then by all means, knock yourself out
with analog.  And I do like popcorn, but the eating kind not the ear kind...  For me,
what Tom is referring to is the idea that more bits of resolution and higher sample
rates tend to approach "perfection" as they increase.  There can come a point where
they surpass "analog" methods using real baryonic matter parts that can be obtained
even today IMO.  And then the digital model you have can be if you prefer,
intentionally corrupted mathematically for some specific purpose or noise profile.

I Am curious to know why you want this particular distribution.  What is the
application if I may ask?



>So, there you go! Have I convinced you yet?! I'm just playing 
>devil's advocate, really. I don't care either way. Do it with 
>analogue if you can find a good way. 
>
>Regards,
>Tom
>
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