Tracking Generators

[Rich Holmes]

rmiller at pangea.ca (Deathlehem - experience the joy) writes (on AH):
>Uh oh.  Now you've done it Mike!  I want a tracking generator for Bernie, my
>modular.
>How to build one in the analog world though?  I've just been through 3 ideas
>quickly, and this one sounds the best so far:  (Anyone else interested in
>developing one of these, email me.  Once I/we have a design worked out I'll
>prototype it, and put all of the developement data on my webpage).
>
>- I figure a number of pots being fed a voltage.
>- 1 pot for each 'step'
>- The pots are fed sequentially (one by one) into a multiplexer that sends
>the voltage available from each pot at a time across a charging/discharging
>capacitor into a buffer opamp.
>- The buffer output then controls a VCA's output which has the CV to be
>'tracked' (Not really the correct word here, but ....) fed into it's input.
>- The multiplexer is clocked by any available clock.
>- With a proper switching arrangement, the Tracker could be made to move
>from 2 to x number of stages (depending on what type of demultiplixer is
>used: 4, 8, 16, etc.
>
>Gurus?  Is there any error in this plan?  Anyone else have any input?

Well, Mike's explanation left me confused as to exactly what the
nature of the tracking generator's transformation is.  E.g. apparently
you can use it to convert, say, a linearly rising control signal to
one that's flat for a while, then rises steeply.  But what would it
do, if similarly configured, to a falling signal?  A flat one?  If I
understand your interpretation, it's that it multiplies the control
signal by another one which is continuous and piecewise linear.  Is
that what you (Ric) had in mind, and is that what you (Mike) were
describing?

Your analog analog (if you catch my drift) sounds like a VCA driven by
what might be called a slope sequencer: a sequencer programmed to put
out a sequence of, not levels, but slopes.  Such a sequencer in and of
itself seems like it'd be a nifty module.

If I've completely misunderstood either or both of you, please apply
gentle correction...

-- 
- Rich Holmes

    "Not every tradition, however entrenched, is attractive.  Some
	 should be closed down immediately." -- Miss Manners