Analog Sequencer Poll

[J.D. McEachin]

On Fri, 13 Dec 1996, Magnus Danielson wrote:

> > I have in front of me here an ARP Sequencer manual. On the ARP sequencers,
> > they have this funky random mode, where it picks out which notes to play at
> > random... how would ya implement this ? (without using a CPU!!!). I had the
> > idea of using a high speed oscillator, and selecting voltages off it
> > periodically... would this work ?
> 
> One simple method of generating pseudo-random numbers is by using a shift
> register and a handfull of XOR gates. They can cheaply be created with quite
> long length and very long sequence before repetion occur. I don't know if this
> is the method used in the ARP Sequencer, but it could very well be. A few
> resistors and a op-amp buffer and hey, you got random notes...

Using a HF scanning oscillator gives a repeating pattern, but, depending
on the ratio of its frequency and the clocking frequency of the sequencer,
the period is so long as to appear random.  This periodicity can be
musically useful.  If you make the HF oscillator adjustable (and better
yet, syncable), you can obtain repeatable scanning patterns (especially
when the scanning oscillator's frequency is slightly higher than the
clocking oscillator's). 

JDM