pseudo-random shift generator

[David Halliday (Volt Computer)]

The schematic can be found at
http://www.tellus.vallentuna.se/gymninfo/personal/anders/andersus.html
and was published in the 1970's by Electronics Today International
magazine.

It is a five megabyte PDF file so be prepared for a bit of a download...

Some interesting design ideas - the filter is implemented with a
switched capacitor network, the ADSR is a bit different and has some
flexibility...  I would probably not copy it but it is a good source for
ideas for current designs!

Art of Electronics ( Horrowitz and Hill ) has some stuff on the shift
registers ( page 655 or so ), Hal Chamberlin's book "Musical
Applications of Microprocessors" has a nice writeup on it too complete
with design ideas and things to watch for.



> -----Original Message-----
> From:	jc at lynx.bc.ca [SMTP:jc at lynx.bc.ca]
> Sent:	Tuesday, September 16, 1997 11:30 AM
> To:	synth-diy at horus.sara.nl
> Subject:	RE: pseudo-random shift generator
> 
> >The circuit in question ( ETI 4600 page 20 )
> 
> I don't think I've ever seen that publication anywhere ... actually
> I'm
> more interested in the chips used (their #'s) and the kind of gate
> used to
> "stir" the sequence and as well pin-connections ... someone once
> verbally
> described these circuits to me and so I've got an idea of what's going
> on
> here ... maybe someone could provide me a textual description that
> gives
> enough info so I can experiment on this ... I've heard that registers
> of
> prime order (3,5,7,11,13 ...) are best to use with this technique ...
> 
> btw, I was thinking of using a shift register whose internal bits have
> individual pin-outs to ease manipulation of signals and in-circuit
> testing
> and variations ... even without this I suspect that two plain shift
> registers (with only one in and out) can have their outputs combined
> and
> nored/exored/whatever to be used as a new input for one side of the
> signal
> chain (this is what I mean by cross-coupled) ... I can very well
> understand
> how the authors of the circuit you mention would provide a serial
> expansion
> to the classic shifter/generator circuit but that to me is the lazy
> "engineering" approach ... a parallel expansion should be much more
> economical and generate much more complexe sequences then the serially
> enhanced circuits ... perhaps cross coupling two shift circuits that
> have
> differing lengths is the way to go ... in which case a register with
> available outputs on each bit would make sequences easily switcheable
> ...
> just a hunch ...
> 
> jc
> 
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