pseudo-random & slow random ?

[Martin Czech]

This mail got lost, so again:

SNIP
> One thing to be aware of is that the *choice* of taps can have a great effect >on the max length of the pseudorandom number generator as well as whether the c>ircuit will sustain a long and repeatable sequence.  Take a look at the equival>ent circuit of the MM5837 - simple (2 taps, 17 stages) and long.  Intuition say>s that for every stage (bit) added, you double the length of the sequence.
>
SNIP
Thats true. A shift register with length N has 2**N combinations.  So
it won't take much more effort at all to get a very long sequence.  The
question is how to set up the feedback and exor stuff so that all
combinations are walked through.  We use such pseudo random generators
for built in self test of our dsp chips sometimes, and I have a
table somwhere  of the minimum effort of feedback circuitry for a given
lenght N. I remember that some long registers had surprisingly few feedback
expressions so it was economic to make the sequence longer !

If someone is interested in that table, I dig it up out of my heap of
shit on my desk (sorry, I had to say this). This can take quite a while.

On the other hand I have to say that I find the idea of "real" analog
noise nicer. Because if one derives trigger signals or very low
frequency random voltages out of it, they won't repeat. I like this
self playing machine stuff, if it is  set up carefully. Now, trigger
signals is no problem, but what about slow random? If I try to do this
purely analog, i'll have to use some lp-vcf. This will yield very small
output voltages (well, all the high frequency stuff has gone) and I
guess the offset voltages will be in the same range. This would mean
that the error voltages (which are not random, but depend on frequency
controll voltage) are larger then the wanted signal.

Are there any ideas how to solve this problem ?
How can I get rid of the damned offset ?

Maybe a pseudo random with low clock frequency ?
Perhaps some analog noise added to the feedback loop operation ?
A switched capacitor or resistor time discrete filter?
Filtering in hf and shifting the noise band via multiplication (modulation)?
Cascading simple 6dB lp one poles with jfet as resistor?

Please, some help !

m.c.