Mad Man Rambles about Noise Generators

[Scott Gravenhorst, Synthaholic]

You wrote: 
>
>>	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.

Why?  It is not a cascaded flip flop binary counter, but rather each 
stage passes it's bit value to the next stage on each clock.

Let's remove the scrambling XOR feedback for a moment and consider a 
simple 8 stage shift register.  Assume a constant clock rate and that 
the register starts clear.  Now assert and hold a high level at the 
input.  8 clock times later, the output of the last stage goes high.  
Now extend it to 9 bits and do the same experiment.  Wouldn't the high 
level appear 9 clock times later?  If a feedback loop is added without 
XOR, but simple inversion, would this not represent a divide by 16 (8 
clocks high, then 8 clocks low...) in the first example and a divide by 
18 in the second?  I should think that 16 stages would be required to 
extend the delay to double that of an 8 stage register.

>
>>   I am also going to experiment with a PLL attached to the noise 
>>   generator output. 
>
>What's the purpose of the PLL?

Since the ouput of any stage toggles between high and low, it's output, 
if taken to be analog, is of constant amplitude, but varying frequency. 
Inputting this single bit output into one side of the PLL phase 
comparator, the PLL demodulated output would produce a varying 
amplitude signal of random frequency as well as random amplitude.  I 
would think that it would have a different sound than the raw digital 
signal of one shift register flip flop output.

Would this be the same as simply lowpass filtration?  I don't know.  
That's why I want to try it.

-- 
-- Scott G., Synthaholic

If at first you don't succeed, keep suckin' 'til you do suck seed.
                                                 -- Curly Howard
What else can happen?
       -- Howard (Never call me Howie) Bradley