AM Synthesis

A friend (in another part of the country) with access to Buchla hardware, sent me a short demo video so that I could hear the wavefolding range on a CO and also how the timbre change with AM as the modulation depth of the modulating oscillator (tuned a 5th higher than the CO) was cranked up – both with and without wavefolding involved.

One of the things that stands out is that the character of the Buchla’s AM has more clangor and growl when the amount of modulation is cranked up than when I try it in Audulus or the demo version of the Arturia Music Easel clone. There is also kind of a beefier low-end. I should probably compare spectrograms to see if anything stands out.

I was wondering if anyone has thoughts about what might contribute to this. I suspect that this is not just an analog vs. digital thing.

Any pointers on where I might look in terms of playing with the math?

Can you link to the audio example?

Here is a zip archive with some samples:

In the folder are the following files:

  • 0 Complex Slightly Folded - this is the complex oscillator with the timbre slighter about 1/8th of the way up. the waveform of the CO is set to sine
  • 1 Modulator Triangle - brief recording fo the modulatiion oscillator. It is set to triangle and is tuned one fifth higher than the CO
  • 2 Wavefolded Complex Modulated - modulation mode set to AM. This is the slightly wavefolded CO being modulated. The modulation depth goes from zero to max then back to 0.
  • 3 complex no wavefold modulated - this is the CO with no wavefolding with the modulation going from 0 to ma and then back
  • 4 Complex Modulated changing wavefolding and modulation - starts with the non-folded complex oscillator followed by the wavefolding (timbre) being increased a little then modulation brought up a bit and modulation and wavefolding being brought up at different rates (by hand) and then back down to give a sense of the timbral range.

If you goof around with the Cross Mod module in this patch you can get there I think. It sounds like the width on 3 and 4 is just the bell like harmonics you get with FM/PM synthesis.

Also, @robertsyrett’s “strings” synth voice is brilliant. If you scroll down, I did a “string test” post on soundcloud. Toward the end there is a very convincing bow like sound when I played chords with a particular envelope. The thing with that though, is it starts off in Audulus as the voice, but then I ran it through the Make Noise LXD, with the Pulp Logic Cyclic Skew controlling that low pass gate. But, IMO, it does have the width you are after.

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I am setting up a project to make it easy for me to swap in AM methods and different wavefolders to compare different methods. So far, it is very elementary. My next step is to add a muxer and push button to be able to switch between different methods.

AM Explorer Simple wf .audulus (88.9 KB)


Here is a draft of project I put together to more quickly help me compare AM methods. It is pretty crude. I’ll add some way to expose the VCA controls. Still learning the ropes of how to propagate user interface to the surface. I hope V4 will make it possible to propagate a patch’s ui elements to the surface.

I could also use pointers on how to make the cords less messy (especially with demuxes and the like).

AM Explorer Multi 0.9.audulus (163.8 KB)

Thanks for the suggestion. I’ll have another look at it. One of the things that I am looking for is not just how to replicate an individual setting but coming up with a responsive system whose algorithms and parameter ranges, etc. are setup not just to be able to accomplish a wide range of sounds but also so that it is easy to find the sweet spot. I read a discussion where some people were discussing various complex oscillator based systems. One remarked how he found that while the several complex-oscillator based systems were capable of replicating each others sounds that some COs are much easier to find the sweet spot and manipulate usefully in realtime than others.

What that would be is probably different from person to person. So, this exploration is helping me figure out what that would be for me.

In the explorer patch that I just posted, the results are quite different with a few VCAs.

Here is a better version of the AM explorer. I adjust the settings of the various VCAs to adjust perceived volume and the settings of the individual VCAs so that they don’t clip too much. For a fairer comparison, it would probably better to expose some of their controls so that one doesn’t have to go inside the AM module.

Here it is in all its ragged glory:

AM Explorer Multi 0.93.audulus (185.8 KB)

AM Explorer Simple wf (Bass Bins).audulus (1.1 MB)

  • That vca switch in the other patch is a good time.

Cool patch. It looks like the modulator oscillator became disconnected in your version. Was that intentional? I connected it back after downloading then had a lot of fun playing with it.

The last version that I uploaded has 7 AM mid flavors to play with.

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That’s funny I didn’t notice. Because you can pretty much route anything in Audulus, when I hear something I really like from patching here and there, it often leaves some key element out. In this case, basically the main part. It’s always interesting when you stumble upon new tones you have never landed on.

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Here is a much more interesting version of the Amplitude Modulation explorer.Hopefully it is self-explanatory. I’ve added text in all the sub-patches with explanations for anything that might not be obvious. It is ugly looking, but then again it is really a research tool at this point as opposed to an instrument.

I’ve added some envelopes you can wire in and Roberts dynmc module from 0-Toast. Also, you can toggle between using MIDI input or a rudimentary tuned pulse.

I think it is now a useful tool. And I am finding the tonal possibilities of the different AM methods interesting and not subtle.

I plan to do a similar exploration for wavefolders and FM algorithms.

I’ll also make it easier to change where the wavefolding happens:

AM Explorer Multi 0.942.audulus (252.5 KB)

Coming along. Next step is adding FM. This new version has a double pulser which is fun for creating polyrhythms. To use one pulser only, set the other pulser to 0. Use the ‘resync’ button to resync the two pulser. It can be fun to play the resync button to create nice rhythms. I also dropped in the reverb from @robertsyrett’s Cortini drone patch. This version has lots of attenuverters and AR’s to create fun modulations.

I hope you will have fun. If you play with these, I would love to now which AM-type you prefer:

AM Explorer Multi 0.945.audulus (394.6 KB)


OOPS! I just noticed that the version of the patch that I posted has the level knob disconnected in the output patch!

Sorry about that.