bizarre thoughts (was: AW: Saw-to-Tri converters)

Haible Juergen Juergen.Haible at
Tue Nov 25 10:40:35 CET 1997

	>Paul Perry wrote:
	>> ......the MS20 is the most bizarre & unorthdox bunch of
circuits I have
	>> ever seen..... but when looking for cheap/simple saw to tri
convertors think
	>> about what they are going to be used for..  an audio sine
wave in a synth can
	>>  have 10% distortion and blips all over it and you can't hear
it.... but
	>> slow it down to 0.2 Hz and modulate an oscillator with it and
you have
	>> TROUBLE and tears..... as always, horses for courses....
	>Yes indeed, i like the filter construction of the MS20.

To me, the MS-20 always was #2 of bizarre synths, the VCS-3 being #1.
One thing that I always found annoying on the MS-20: the HADSR envelope
is hard-wired to the VCF, while it would make great sense to have HADSR
on the filter and the simple AR on the VCA.

But the HADSR is a great thing: Trigger a note with looong Attack
and let it evolve while you go on playing your other synths. 

Too bad that I haven't implemented HADSR on my JH-3 Modular. So
I had to emulate the Hold with another AR envelope.

This brought me to another idea:
If you play HADSR like I described above (hit a note and go away), you'd
like to have another parameter I would call "Gap Time".

I patched the following setup:

Gate (from Kenton Pro-2, with Retrigger On) goes into an AR envelope
and into an AD envelope at the same time. Both "A"s are set to zero,
the Release of AR works as hold time, the Decay of AD works as "Gap
Time". Now the outputs of both AR and AD go to an EXOR gate,
and the output of the EXOR then serves as Gate signal for the main
ADSR envelope.
Try this: long ADSR-Attack (for slow fade in), long AR-Release (=Hold
medium ADSR-Release (for medium fade out), and a medium AD-Decay
(=Gap Time) to match the ADSR-Release.
DEcay and Sustain of ADSR are set to medium or high values as well.

Now what happens is this: You hit a note shortly, and after some delay
(Gap time), the sound fades in. Now what happens if you hit a note
again, while the Hold phase is still active?

Without the "Gap Time", not much would happen. The envelope would be
again, but that would mean that the note would simply stay on - very
With the "Gap Time", the Release phase of the ADSR would start as soon
as a new note is triggered, and you would get a fade out first, until
GAP Time is over, and then the The retriggered Hold Phase would take
and the sound would fade in with a new slow Attack phase from the ADSR.

You can play very beautiful melodic lines with such a setup, and of
you can change the overall envelope times by varying the time you press
the keys, or by repeatetly pressing a key and so on. Hard to describe,
very impressive if you try it.

Now I plan to build a simple function for this, with 2 potentiometers
very minimal envelopes, just to have a standalone Hold/Gap module.
You can use this module for 3 functions:

(1) normal Hold function 
(2) normal Gate Delay function
(3) Hold & Gap function.

Hope you found this interesting.


PS.: If I ever build a little "Solo" Synthesizer, it will get such a
        as main envelope, the VCS-3 Trapezoid as 2nd envelope, and a 
        combination of MS-20 HPF and VCS-3 VCF as filter.  Marriage
        of the 2 most bizarre little synths (;->).

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