Mad Man Rambles about Noise Generators

[Don Tillman]

   Date: Fri, 31 May 1996 21:42:28 -0700
   From: chordman at ix.netcom.com (Scott Gravenhorst, Synthaholic)

   It occurs to me that there is more to the size of the shift register
   than simply the repeat time.  There is a question of spectrum size as
   well.  

Well yeah, I thought this was pretty well understood.

A device with N flip flops is going to have, at most, 2^N states.  A
feedback shift register with XOR gates is just going to scramble the
order of those states.  

	  It would seem to me that a shift register of 16 bits would be 
   able to produce noise an octave lower than one of 8 bits, but that the 
   high end of the spectrum would be controlled by the clock rate alone in 
   both the 8 and 16 bit versions.  Assuming, of course, a constant and 
   equal clock rate for both.  

Ummm, no.  A shift register of 9 bits will be able to produce noise up
to an octave lower than an 8-bit register.

   I am also going to experiment with a PLL attached to the noise 
   generator output. 

What's the purpose of the PLL?

  -- Don