[sdiy] Continuously variable waveshaping (was Behringer Neutron)

[David G Dixon]

@Rutger: The Dixie is a tricore with a comparator, zeners to provide a 5Vpp
square wave, and an expo 2164 VCA controls the loop current for 1V/Oct and
Expo FM.  A additional linear VCA in the loop provides Linear FM.  The
square wave is fixed at 50% duty cycle by the comparator, unless the
comparator input is synced.  However, all sorts of things are possible with
this configuration, and altering it to get Moog's waveforms wouldn't be that
much of a struggle.  I'll just leave it at that.


  _____  

From: Rutger Vlek [mailto:rutgervlek at gmail.com] 
Sent: Wednesday, April 11, 2018 1:39 AM
To: David G Dixon
Cc: 'Tim Parkhurst'; 'synth-diy at synth-diy org'
Subject: Re: [sdiy] Continuously variable waveshaping (was Behringer
Neutron)


It's an interesting read, this patent! And I wasn't even aware Moog was
actively filing new patents in recent years. 

@David: I didn't know that about the Dixie. And I'm not sure if I understand
you correctly. You mean the Dixie runs on a triangle core, and the
implementation of the tri-core requires a comparator that provides you a
pulse output of which you can modulate the duty cycle? How can that change
rise and fall time of the triangle, then? It would have to be combined with
a change in the expo CV right to achieve that? Or am I missing something?

Regards,

Rutger



On 10 apr 2018, at 19:59, David G Dixon wrote:


All I could see of the patent were the figures, but based on that, it looks
a lot like what happens in the Dixie.  All of the "modes" shown in the final
figure could be obtained simply by duty-cycle control of the driving square
waves in a tri-square oscillator.


  _____  

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Rutger
Vlek
Sent: Tuesday, April 10, 2018 6:34 AM
To: Tim Parkhurst
Cc: synth-diy at synth-diy org
Subject: Re: [sdiy] Continuously variable waveshaping (was Behringer
Neutron)


I recently stumbled on this recent patent by Moog:
https://patents.google.com/patent/US20160335998A1/un

It concerns continuously variable waveforms, but implements it at the core
of a VCO rather than by crossfading the outputs (waveshapers) of one. The
idea is awesome, but I have my reservations about the real-world feasibility
of the method (given component tolerances and accuracies).

Rutger



2018-04-08 21:09 GMT+02:00 Tim Parkhurst <tim.parkhurst at gmail.com>:


" 'High frequency hash' is a direct quote from Ken Stone's description of
that
circuit, by the way." 


- and the band name for my new EDM / free jazz group. 



Tim (add in some corned beef and you've got a tasty breakfast) Servo
---
"Imagination is more important than knowledge." - Albert Einstein





On Sun, Apr 8, 2018 at 11:36 AM, Guy McCusker <guy.mccusker at gmail.com>
wrote:


On Sun, Apr 8, 2018 at 6:54 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> My wavefolder (as found in the Intellijel uFold) uses TL072, and doesn't
> generate "high-frequency hash".  Also, I've achieved what looks a lot like
a
> resonant filter output with a sawtooth wave, without a filter.  Given the
> way that this folder works (with diode "turnaround" circuits) I'm not sure
> that slew rate is a significant factor.  The opamp outputs in the folder
> chain are confined to relatively small voltages -- the first one to about
3V
> or less, and the subsequent ones much less.  Other folders may have
> significantly different modes of operation where slew rate is important,
but
> not the ones based on diode turnarounds.

There's a bit of talking at cross-purposes here I think. The wave
folder in the CGS29 and also the Serge wave multiplier (middle
section) also does not generate "high frequency hash" and works fine
with a fast op amp. Their design is also similar to your "turnaround"
idea, as it happens.

The "high frequency hash" business concerns a different part of the
CGS29, the Grinder section, which exploits op amp overshoot and
ringing. It makes sense that slew rate is a factor there. ("High
frequency hash" is a direct quote from Ken Stone's description of that
circuit, by the way.)

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