Tim,

I'd be willing to bet you a patch-cord that those minus 4 comes from a
miscalculation somewhere. It would be a lot easier to designing an
algorithm or a circuit with a cycle length of 2^18 straight than
2^18-4 as for the latter you would need to reset the bit pattern at a
specified point. With two 4 bit shift registers and two 5 bit ones you
might conceivably design one with a length of (2^4-1)^2 * (2^5-1)^2
but even this would be harder than designing one with an exact length
of 2^18 and there would be no good reason to do it (at least not for
the purpose in question)

/Silas

On Tue, May 6, 2008 at 11:20 PM, Tim Stinchcombe
< timothy@... > wrote:

>
>
>
>
>
>
> > I'm now pretty sure the sequence is at least 2^19 = 524288 long, so
> at
> > 1kHz (approx knob setting 4), it will take nearly 9 minutes to
> repeat.
>
> With a little computational help from the kind people on the Synth DIY
> list, and some cajoling to get me to run some calcs myself, I can
> confirm that the sequence length is actually 262140 = 2^18-4. Kind of a
> strange number, but I'm working on shedding some light on it!
>
> Tim
>
>