[sdiy] Continuously variable waveshaping (was Behringer Neutron)

[Guy McCusker]

I forgot one more example of a waveform scanning setup: Ian Fritz used his
multiphase oscillator to drive a collection of VCAs to fade between
waveforms.

http://ijfritz.byethost4.com/sy_cir11_68phase.htm

It’s not quite a fully controlled morph between multiple waveforms because
you can’t go back and forth at will but it sounds great.



On Sat, 7 Apr 2018 at 10:07, Guy McCusker <guy.mccusker at gmail.com> wrote:

> I've been tinkering with this sort of thing for a while so here's a
> collection of existing circuits that I know about.
>
> As Vladimir says, the obvious way to do this is to use a bunch of VCAs
> and control them as many-way crossfaders somehow. Mutable Instruments
> Frames does this with 2164s in a very flexible way. Gosh, things are
> easy once you have a micro controller at your disposal.
>
> In the analog realm, the first version I know of is Jürgen Haible's
> interpolating scanner.
> http://jhaible.com/legacy/tonline_stuff/jh_ipscan.html
> This uses a chain of ramp-to-triangle converters with different
> thresholds to generate the control voltages for the VCAs. I think that
> is similar to what the Doepfer A-144 does. David Dixon's recent design
> is kind of similar in its idea if not execution, but does ramp to
> trapezoid conversion and is more controllable.
>
> Don Tillman came up with a different design for the scanner controller
> http://www.till.com/articles/scanner/ which produces nice curved CV
> (actually, control current) sweeps for the VCAs (actually CCAs).
> Haible used this idea for the second version of the scanner
>
> http://jhaible.com/legacy/interpolating_scanner_and_scanv/jh_interpolating_scanner_and_scanvib.html
>
> The Tillman circuit seems to have something in common with Barrie
> Gilbert's scanning controller in this patent
> https://patents.google.com/patent/US5077541
> Gilbert later came up with a linear version of this:
> https://patents.google.com/patent/US5432478A/
>
> I'd love to know whether Don Tillman was aware of the Gilbert design
> when he came up with his one. Don... if you're reading...?
>
> These scanners work really well for morphing between the wave shapes
> from a single VCO, because the sources are all nicely in phase. When I
> built up the Tillman circuit I sat looking at the scope for far too
> long, watching a sawtooth fold itself over into a triangle, then
> soften into a sine, and back. But like Vladimir, I bet Behringer are
> using a microcontroller.
>
>
>
> On Sat, Apr 7, 2018 at 7:33 AM, Vladimir Pantelic <vladoman at gmail.com>
> wrote:
> > given that Behringer can buy 2164s cheap, I bet it's a bunch of these,
> under
> > CPU control...
> >
> >
> > On 06/04/18 21:55, Mike Beauchamp wrote:
> >>
> >> I've seen continuously variable waveshaping on a few different synths
> >> (Voyager, Kobol) and now the Neutron. I've always wondered how this was
> >> done, but have never found a schematic for this. Any examples available?
> >>
> >> Mike
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