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 Forum index » DIY Hardware and Software
FM with triangle-core VCOs
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Peake



Joined: Jun 29, 2007
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PostPosted: Sun May 18, 2008 7:45 pm    Post subject: FM with triangle-core VCOs Reply with quote  Mark this post and the followings unread

The Buchlas produce exponential FM tones unlike sawtooth core oscillators. The overtone content is more limited and sweeter, yet can easily be driven into chaotic results (pitched noise).

Ian is working on a new triangle-core oscillator with very wide-range tracking, and the Thomas Henry VCO-1 is reputed to be a triangle core. I look forward to hearing sine-to-sine FM experiments on each.

For those who are interested in deep index FM, I can see why "stability" could be of concern. As the results would be far more interesting than with sawtooth oscillators, that is. My question is, is stability, even to digital mimicry, important to you regarding such FM depths? A touch of natural noise in oscillator pitch just ruins things completely?

Example of Buchla FM, IIRC including all "noise" tones:

http://virb.com/peake, click play. Is the pitch movement too much for your tastes? Note that this was using a vintage Buchla power supply, not an Eagle or Power One.

This is to increase interest in triangle-core oscillators. The Plan B's FM index isn't as deep, but could probably easily be modified. Topp's upcoming through-zero VCO is triangle-core, right? I'll need a few of those Smile
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cbm



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PostPosted: Sun May 18, 2008 8:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Nice example

-Chris

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v-un-v
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PostPosted: Mon May 19, 2008 1:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Great track Peake! Very Happy
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asafnetzer



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PostPosted: Mon May 19, 2008 4:03 am    Post subject: Reply with quote  Mark this post and the followings unread

Very nice Mike, would have never guessed the source.
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Peake



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PostPosted: Mon May 19, 2008 8:28 am    Post subject: Reply with quote  Mark this post and the followings unread

While I'm happy with my track, I'm not intending to pimp it- I want to generate interest and discussion among those who can create such things! It's a timbral range that some either aren't aware of or don't yet have access to. I'm looking to find all of the sources, and to confirm this sort of behaviour in other triangle-core oscillators. Any thoughts or demos???
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GlassX



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PostPosted: Mon May 19, 2008 8:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

What a fantastic topic! And just in time...

I'm not as experienced as Mr Fritz and Mr Henry, I am finishing my triangle core VCO too. It is a completely novel and very simple design. It also switches to a sawtooth core with just one switch. I have it working on a breadboard already, but I'm gonna build a dual version as soon as I can. The FM simulations on SPICE sound great. I tried using thru-zero and it works, with the advantage that it is **VERY** simple to implement on this core. No, I mean EXTREMELY simple - maybe easier than Sync. By building a Dual-VCO module, I can use the Schmitt-Trigger of the first oscillator to reverse the direction of the second.

It works fantastically and I'm just doing some preliminary tests to reduce the offsets and improve thermal stability. I'll try better op-amps and a tempco resistor...



I'm also experimenting a lot with waveshapers, but even as a huge Buchla fan (can you tell? Rolling Eyes), I'm not much impressed at all with the Buchla Timbre-Symmetry-Order scheme. The low-order part is just a wavefolder, easily replicable with FM just by having a carrier at the same frequency. The high-order part (absent on the Music Easel) is just a clever mix of regular waves. I'll probably not use timbre modulation at all Confused Maybe a PIC and some wavetables? Who knows! Smile

PS: Your track sounds awesome! I downloaded it to my iPod! Surprised

Last edited by GlassX on Mon May 19, 2008 8:41 pm; edited 1 time in total
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Peake



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PostPosted: Mon May 19, 2008 8:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Very interesting- I look forward to hearing and seeing it, and perhaps building it Very Happy
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Norman Phay



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PostPosted: Tue May 20, 2008 3:41 am    Post subject: Reply with quote  Mark this post and the followings unread

The only tri-core VCOs I have are a pair of the Plan B ones, I've experimented with having them modulate each other at the same time, but only with the lin FM input for some reason. I'll have a try with exp fm when I put together this powersupply box I have here. All the other VCOs I have - a pair of ModCan, a pair of MOTM, three Wiards and a single Blacet are saw-core to the best of my knowledge. I'm just finishing up a pair of Oakley VCOs, I've got one going, the other just needs the remining wires soldered in behind the panel. Although they all sound (quite surprisingly) different in their raw state, I don't hear any particular sonic signature that sets the Plan B ones far apart from the others. They are very good oscillators, though, I'm pleased with them.

The Oakleys seem to have the widest-ranging FM depth out of the ones I own, this could be an interesting thing to talk about on another thread, maybe on the modular synthesis sub-board - how different features are implemented across different versions of "the same thing". It's certainly good to have different manufacturer's oscillators because of this.

I've had that impart tangent piece in my computer ever since you posted it on either AH ot T-G-S a while ago, Mike. I think it's very good, when I look in my music mp3s folder, it's often the first thing I'll put on.
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3vcos



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PostPosted: Tue May 20, 2008 2:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Wiard VCOs are Triaingle core!

Norman Phay wrote:
All the other VCOs I have - a pair of ModCan, a pair of MOTM, three Wiards and a single Blacet are saw-core to the best of my knowledge. .
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Peake



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PostPosted: Tue May 20, 2008 4:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

3vcos wrote:
Wiard VCOs are Triaingle core!


Really? Are you pulling my leg? Wink I've only heard linear FM on those- does anyone have exponential sine-to-sine FM MP3s?
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3vcos



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PostPosted: Wed May 21, 2008 5:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Yup, I'm certain they are. That said, I'm having a hard time remembering where I got that info. I've spoken with Grant numerous time and been on his yahoo group for quite a few years. I have a feeling I picked it up from him or his wiard yahoo group.
I briefly owned a Wiard VCO and regret selling it very much.


Peake wrote:
3vcos wrote:
Wiard VCOs are Triaingle core!


Really? Are you pulling my leg? Wink I've only heard linear FM on those- does anyone have exponential sine-to-sine FM MP3s?
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ryktnk



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PostPosted: Wed May 21, 2008 6:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello

Do you mean the FM input of the 258 module, or the control input ?

The FM input is linear, the control input is expo.

I have tried to test this with the TH vco1 and the Electronotes TZO.

Both oscillators needed to have the FM input "untamed" a bit for
stronger depth, also taking off the DC coupling helps for stronger
sound.

Using linear or expo FM on both VCO's creates some pretty crazy
sounds, but not "noise" in the random sense.
Patching a 2nd modulation oscillator into the FM gives much more
noise-like unpredictable sound.


-ryktnk
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Peake



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PostPosted: Wed May 21, 2008 7:44 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi, the Buchla 258c has linear FM and can be identified by the three audio outputs per oscillator. The B and as far as I know the A and all 1xx models had exponential FM. Also IIRC the 258b has a cap in the FM input path. I may be hooking up a soundcard this week so I'll post solo examples if possible.

The best linear FM I've heard is also on the Wiard...
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shebb



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PostPosted: Wed May 21, 2008 5:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

sounds great

a couple questions, hope it doesn't count as a hijack...

is the difference between linear and exponential just a matter of CV input scaling.

also, why is thru zero any better than this?
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GlassX



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PostPosted: Wed May 21, 2008 5:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

shebb wrote:
is the difference between linear and exponential just a matter of CV input scaling.


Yep! Exponential is just 1Volt/Octave modulation. Linear is Volts/Hertz modulation.

Quote:
also, why is thru zero any better than this?


Thru-zero is just linear frequency modulation with time-reversal. Meaning that the carrier oscillator reverses direction when the modulator changes polarity. For me, it is just a fancy term for Sync. I like it because it locks one oscillator to the other, making tuning muuuuch easier.
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Peake



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PostPosted: Wed May 21, 2008 5:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

That would be a hijack, but it appears that my questions may go unanswered, so I say let there be hihack Laughing
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GlassX



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PostPosted: Wed May 21, 2008 6:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
That would be a hijack, but it appears that my questions may go unanswered, so I say let there be hihack Laughing


I believe I sort of answered to your stability question on my last reply already Very Happy

Regular linear FM needs HIGH accuracy. I've seen Buchla 200e users complaining that some settings make the carrier oscillator sound out of tune. That's not the 200e fault - just how regular linear FM works.

With the time-reversal sync thingy you can have the two oscillators sort of oscillating together, so, drift will sound like regular vibrato and won't change the timbre, make terrible noises or make your output sound out of tune.
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Peake



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PostPosted: Wed May 21, 2008 6:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

GlassX wrote:
I believe I sort of answered to your stability question on my last reply already Very Happy


Yes, and thank you, and thank you for presenting your project! I'm now after audio examples of the TH VCO-1 and Ian's, when it's available, to see if the Buchla has something that no other does.

GlassX wrote:
Regular linear FM needs HIGH accuracy. I've seen Buchla 200e users complaining that some settings make the carrier oscillator sound out of tune. That's not the 200e fault - just how regular linear FM works.

With the time-reversal sync thingy you can have the two oscillators sort of oscillating together, so, drift will sound like regular vibrato and won't change the timbre, make terrible noises or make your output sound out of tune.


Linear FM does very little for me, and I wouldn't care if it never appeared on any oscillator in my setup...through-zero, if it approximates Chowning FM, would be very desirable, however...
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GlassX



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PostPosted: Wed May 21, 2008 6:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Peake wrote:
Linear FM does very little for me, and I wouldn't care if it never appeared on any oscillator in my setup...through-zero, if it approximates Chowning FM, would be very desirable, however...


But Chowning FM IS linear... Confused

I didn't notice you were talking about Expo FM on the original post... Now, I feel stupid, because I don't even remember when I used Expo FM... maybe just on an ARP2600 to make noise, I believe... Confused
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ian-s



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PostPosted: Wed May 21, 2008 6:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

GlassX wrote:
I don't even remember when I used Expo FM


It would be my preferred input for patching vibrato Smile

I think patching the modulator via a high pass filter would get closer to Chowning style FM, which is actually phase modulation.

There are probably quite a few categories of Chowning FM sounds that don't require high accuracy. Bells for example. A lot of DX sounds detune operators intentionally to add motion etc.
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GlassX



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PostPosted: Wed May 21, 2008 6:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

g2ian wrote:
It would be my preferred input for patching vibrato Smile


Oh, mine too! But I was only thinking about audio-rate FM Very Happy
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shebb



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PostPosted: Wed May 21, 2008 6:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Very Happy for me this was a very informative hijack!

I'll probably end up staring a topic anyway, this thru-zero stuff is confusing
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Peake



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PostPosted: Wed May 21, 2008 7:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

One of the most informative hijacks I've seen, indeed!

GlassX, if you want, check the first post for a track using a lot of exponential audio-rate FM on unstable oscillators and a very unstable vintage power supply.
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ryktnk



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PostPosted: Thu May 22, 2008 11:45 am    Post subject: Reply with quote  Mark this post and the followings unread

-
Last edited by ryktnk on Sun Oct 19, 2008 11:05 am; edited 1 time in total
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Peake



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PostPosted: Thu May 22, 2008 12:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

Is that this oscillator?

http://musicfromouterspace.com/analogsynth/VCO200604REV01/VCO200604REV01.html

The one that, after all this, says "Saw core design"?
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