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 Forum index » DIY Hardware and Software
Waveshaper for Pulse Forming Synthesis a la Variophon
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Ricko



Joined: Dec 25, 2007
Posts: 183
Location: Sydney, Australia
Audio files: 17

PostPosted: Fri Sep 15, 2017 6:58 am    Post subject: Waveshaper for Pulse Forming Synthesis a la Variophon
Subject description: Transistor Op-Amp circuit
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The Variophon synthesizer is very rare. It used a method of synthesis called "pulse forming synthesis", and this method is in fact almost impossible to replicate by stringing together standard synth modules, even though it is quite simple in concept. So I designed and simulated a circuit for it (TINA-TI) and generated some out audio, as a step to stimulating interest.

The basic idea is merely that the output has a fixed width pulse for every frequency: i.e. not say 50% of the wavelength but say 1ms regardless of frequency. (My implementation is just a comparator driving a monostable multivibrator with a selectable on period. Not complicated.)

What does that do? It allows a particular kind of formant generation, one that approximates pretty much of what happens in blown instruments like reed or brass instruments. There are academic papers on it, but let me explain like this: turn your ideas upside down.

First imagine a standard VCO with a pulse output set at 25% running at 400 Hz. Now imagine that we build a circuit to generate exactly the same wave, but using a sawtooth VCO going through some complex fixed filter (or convolution). Now imagine that you change the frequency of that sawtooth VCO going through that same fixed filter: you get the same kind of equalization or formant pattern, but it affects different harmonics now.

And it turns out that this is what happens when you have a fixed pulse waveshape, and you vary the space leaving the mark constant. This is "pulse forming" synthesis.

My implementation has two wrinkles: first when the note goes high enough that the pulse gets to 50%, it won't go more than 50%. And second, it allows you to mix in extra fundamental by having a fixed LPF at around 100Hz. Otherwise low notes get mighty thin.

Here is the circuit.


blipblop55-01.jpg
 Description:
Example waveshape at 55Hz and Width knob at half.
 Filesize:  30.95 KB
 Viewed:  1397 Time(s)

blipblop55-01.jpg



CONSTANTWAVESHAPER.JPG
 Description:
Circuit
 Filesize:  143.51 KB
 Viewed:  72 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

CONSTANTWAVESHAPER.JPG



Last edited by Ricko on Fri Sep 15, 2017 8:52 pm; edited 3 times in total
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Ricko



Joined: Dec 25, 2007
Posts: 183
Location: Sydney, Australia
Audio files: 17

PostPosted: Fri Sep 15, 2017 7:06 am    Post subject: Sound samples Reply with quote  Mark this post and the followings unread

And here are various sound samples, generated by the circuit simulator (not built): more in the next emails.

They are static so they don't really convey in isolation the effect. You would want to follow the same width at different pitches, but I have uploaded the files according to pitch, apologies.

They are at 27 Hz, 55 and 220. There are three variations, for different Width settings.


blip-27-01-somebass.wav
 Description:

Download
 Filename:  blip-27-01-somebass.wav
 Filesize:  172.24 KB
 Downloaded:  62 Time(s)


blip-27-50-somebass.wav
 Description:

Download
 Filename:  blip-27-50-somebass.wav
 Filesize:  172.24 KB
 Downloaded:  50 Time(s)


blip-27-99-somebass.wav
 Description:

Download
 Filename:  blip-27-99-somebass.wav
 Filesize:  172.22 KB
 Downloaded:  41 Time(s)


blip-55-01.wav
 Description:

Download
 Filename:  blip-55-01.wav
 Filesize:  172.31 KB
 Downloaded:  49 Time(s)


blip-55-01-no9bass.wav
 Description:

Download
 Filename:  blip-55-01-no9bass.wav
 Filesize:  172.3 KB
 Downloaded:  45 Time(s)


Last edited by Ricko on Fri Sep 15, 2017 7:19 am; edited 2 times in total
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Ricko



Joined: Dec 25, 2007
Posts: 183
Location: Sydney, Australia
Audio files: 17

PostPosted: Fri Sep 15, 2017 7:08 am    Post subject: Reply with quote  Mark this post and the followings unread

More waves


blip-220-99.wav
 Description:

Download
 Filename:  blip-220-99.wav
 Filesize:  172.31 KB
 Downloaded:  46 Time(s)


blip-220-50.wav
 Description:

Download
 Filename:  blip-220-50.wav
 Filesize:  172.31 KB
 Downloaded:  44 Time(s)


blip-220-01.wav
 Description:

Download
 Filename:  blip-220-01.wav
 Filesize:  172.31 KB
 Downloaded:  41 Time(s)


blip-55-99-no9bass.wav
 Description:

Download
 Filename:  blip-55-99-no9bass.wav
 Filesize:  172.31 KB
 Downloaded:  39 Time(s)


blip-55-99.wav
 Description:

Download
 Filename:  blip-55-99.wav
 Filesize:  172.31 KB
 Downloaded:  39 Time(s)

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Ricko



Joined: Dec 25, 2007
Posts: 183
Location: Sydney, Australia
Audio files: 17

PostPosted: Fri Sep 15, 2017 7:10 am    Post subject: Reply with quote  Mark this post and the followings unread

And the last


blip-55-50.wav
 Description:

Download
 Filename:  blip-55-50.wav
 Filesize:  172.31 KB
 Downloaded:  46 Time(s)


blip-55-50-no9bass.wav
 Description:

Download
 Filename:  blip-55-50-no9bass.wav
 Filesize:  172.31 KB
 Downloaded:  46 Time(s)

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g.gabba



Joined: Nov 29, 2008
Posts: 185
Location: berlin
Audio files: 18

PostPosted: Sat Sep 16, 2017 2:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Your attempt to stimulating interest was a succsess
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Blue Hell
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Joined: Apr 03, 2004
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Location: The Netherlands, Enschede
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PostPosted: Sun Sep 17, 2017 2:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

It seems to be the season :: http://electro-music.com/forum/post-430401.html

A very interesting way to generate waves ... it's related to VOSIM and FOF too I think.

Will listen to the wavs soon!

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Ricko



Joined: Dec 25, 2007
Posts: 183
Location: Sydney, Australia
Audio files: 17

PostPosted: Sun Sep 24, 2017 6:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

The Bergatrophon Woodwind waveshaper also is a version of this kind of wave, but producing a triangular blip not a squared pulse.
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Blue Hell
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Joined: Apr 03, 2004
Posts: 22316
Location: The Netherlands, Enschede
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G2 patch files: 319

PostPosted: Mon Sep 25, 2017 5:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Finally listened to the wavs, sounds like a wave with a formant applied indeed - some powerful bass sounds seem possible with this.
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Moosgummi



Joined: Feb 01, 2015
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PostPosted: Thu Oct 05, 2017 11:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Is there a reason you used transistors instead of opamps (or even comparators) and a 555? Great idea to use T2 for limiting PW to 50%, but is the rest just for the simulator?
Great circuit though!
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Ricko



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PostPosted: Thu Oct 05, 2017 7:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

Transistors? The only reason was to limit the different kinds of components. The simulator certainly has comparators and 555s.

I also wanted to have the rising signals in the multi-vibrator available, to be able provide a saw blip out. Having the internals exposed might make it easier to do the Variophon accent thing (slight pulse narrowing and compensating level increase when overblown). I don't think the diff amp comparator is any more complicated in parts count than a comparator chip, and it seemed a good pattern to be aware of. You could certainly implement most of the circuit using a CA3046 (BJT transistor array chip), if you wanted to make it less fiddly to build.

<RANT>Maybe in the back of my mind is the idea that there are all these neat things that can be done almost trivially with a couple of components, and yet we get the same boring tri/sine/saw/sq/pulse waves on VCO after VCO: even Moog went beyond them in the 1970s. I don't know why people put out a new VCO design if it just does the same the same thing as the previous 100 VCOs, or yet another ADSR etc, ...surely adding one extra little unique distinguishing feature per module is not too difficult, like a delay on an LFO etc. Otherwise we end up either with 4HP modules that do almost nothing and $800 modules that do so much, and nothing in between. [Money where my mouth is: I just ordered a Burmuda analog VCO rather than many other choices, because the designer bothered to put in something different, trivially implemented low-hanging fruit.] Anyway, since I don't want to rule the world the next best thing is to have fun suggesting positive little things that can fit in with existing modules. The nice Bergatrophon wind waveshaper is not exactly minimal, so I wanted to show we can get the same family of sounds a bit simpler. </RANT>
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Moosgummi



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PostPosted: Fri Oct 06, 2017 6:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, I´m not too experienced in DIY, so I prefer to have it easy. So when I saw a comparator and monostable multivibrator realized with lots of transistors, I just replaced that in my mind with ICs. Getting signals that aren´t available from them wasn´t even a thing I thought about!
But that´s the way I learn this stuff, by recognizing things I´ve seen before (like T2, I was so proud about that!)
Right now I´m intersted in getting different waveforms out of VCOs, so this (along with Fritz and NLC) is right up my alley.
But your rant touches what modular is about! When I got my Fritz 5Pulser I thought Ok this needs a saw, so I´ll just put it into a saw VCO, more waveforms for me! But then I saw someone putting a tri LFO into it, that was cool too! Might be cool to put an envelope in it as well?
So these 4hp modules doing one thing need just another 4hp module doing another thing, that´s modular.
Also, I don´t think the Bermuda is a good example for a VCO doing something different. All it does is modulate itself, which can be done with every VCO with a cable or (as we build them ourselves) a piece of wire...
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