Ring mod question
  • In the Library of Babel ring mod module, how is the carrier inverted? I see the split, the AM section, and the re-summing, but not how the summing removes the carrier (which in a modular would be accomplished by inverting the non-AM'd carrier). Is it occurring in the summer itself, in some way that's not obvious by inspection?
  • I don't know enough about the fundamentals to answer your question, but for a ring mod, I've just used the math mult node. E.g. For a dalek voice, a 30hz sin osc X the microphone works pretty convincingly.
  • Ring Modulation as a concept is just signal multiplication. If you want to add those other things, use an interver module and a sum module to phase cancel the carrier. :)

    "Ring modulation is [...] performed by multiplying two signals, where one is typically a sine wave or another simple waveform."

    https://en.m.wikipedia.org/wiki/Ring_modulation
  • I've done a little poking around, and have resolved my concern. Please bear with me on this.

    First, here's a link to how I learned (and taught) to do ring modulation on a Moog modular, without using a ring mod module. I think the patch is from Allen Strange.

    http://i.imgur.com/w9SiY9x.png

    The idea is to produce the sidebands on the carrier, then remix that modulated signal with an inverted copy of the original carrier to suppress the carrier in the final signal.

    The significant distinction between ring modulation and simple AM is the suppression of the carrier. If you check the Wiki on "ring modulation" you'll see:

    "This process of ring modulation produces a signal rich in partials. As well, neither the carrier nor the incoming signal are prominent in the outputs, and ideally, not at all."

    What I *didn't* know, because I had forgotten the underlying electronics, was that ring modulation could be produced by simply multiplying the signals. And in fact, later in that same entry:

    "Some modern ring modulators are implemented using digital signal processing techniques by simply multiplying the time domain signals, producing a nearly-perfect signal output."

    Now, if you listen to your ring mod module, you'll hear the carrier quite clearly, because it's re-added to the signal after the multiplier. I think this amounts to AM with carrier.

    *But!* if you remove that added carrier and just listen to the signal of carrier x program, you'll hear the true, klangorous tone of ring modulation (with suppressed carrier).

    Give it a try and I think you'll hear something more like the atonal effect we know and love :-)

    I hope this all makes sense! Let me know your thoughts.

    Oh look... I can attach a file. Let me see if I can upload the screenshot...
    Screen Shot 2016-01-02 at 8.59.11 AM.png
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  • Thanks! Yeah thats a type of ring mod effect but it is not mere ring modulation. Perhaps a more musically useful one and I can add it to the module library no problem.

    Honestly this is really just my personal opinion and mostly based on my interaction with ring mod guitar pedals...but I dont like this effect at all lol, perhaps why I didnt spend too much time diving into it. However I have noticed in places Ive read that its great for percussion (makes sense) so if you dont whip your diagram up I will later :)

    Can you see how to use the modules youve been given to do this?

    Carrier = Sine
    OpAmp Inverter = 1 signal thru inverter module (-),1 signal around or past it (+)
    Blank triangle = Ring Mod module
    Program = your sound source (i.e. What you want to affect with the effect lol)
    Sum = Sum module

    Forgive me if you know this already will be edifying for lurkers tho :)
  • I found it edifying, for what it's worth. :)
  • Just for the edification: in the diagram, the triangles refer to VCAs on a conventional analog modular. One of the nice things about the Moog VCA was that it provided both normal and inverted outputs.

    And yes, the carrier-suppressed ring mod (which is what I still think of as "ring mod" as opposed to AM) is exactly that weird, ugly guitar effect. But well tuned and filtered, it's a great effect for synthesis, particularly of metallic/bell tones.

    And we don't need any extra modules to create it, unless we want to provide level controls and so on. It really is just signal multiplication, apparently.

    What I now really want to work out is frequency shifting. The Bode shifter was basically a ring modulator with the upper and lower sidebands separated into different signals. I don't know if that can be done without circuit emulation (I don't think filters will suffice). I'll have to see if there's a multiplier/summer combo that might get me there.