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Digital Circuits

Discussion in 'Effects [BG]' started by Derek Balonek, Aug 17, 2012.

  1. I believe I've brought this up in a different thread before, but it's still something that I'd like to see. It seems possible and I believe it could revolutionize digital modeling.

    It's simple really; just a digital representation of an effects circuit. We already have circuit modelers such as SPICE, so modeling a circuit is doable. You'd just need a A/D converter to change the audio signal into a digital representation of the voltages, currents, etc. and then you could run it through the circuit. SPICE already has a symbol for a wave input with all the necessary values, so why couldn't it be a signal?

    Think of the things this could do. Instead of modeling the response and behavior of, say, a Big Muff, you'd model its components and circuit and the response would follow. You could have a reasonably close tube tone by modeling an actual tube. And it could be better too, if you'd like. Instead of being limited by the constraints of real components, you could use the ideal. A capacitor with no ESR, an ideal current source, resistors that are exactly in spec.

    I realize there are some difficulties. Specific active components (tubes, transistors, etc) would require a lot of coding. You'd have to input the device gain, it's input and output resistances, stray capacitances and many more variables. But we already have reasonable models of the real thing in modeling programs, so it might not be too difficult. Say, a table with entry points for device characteristics. You could even use the datasheets for that. Perhaps it would even allow for a range of tolerances that it could randomly select from.

    I realize there would be limitations; for example it would be tough to model the output of a power amp as the power supply would have to be big enough to put out the actual swing. I'm sure it would likely require a decent amount of processing power as well.

    Still, wouldn't it be cool to have?
  2. Bassamatic

    Bassamatic keepin' the beat since the 60's Supporting Member

    I think that this is already being done to a great extent. Just look at the Line 6 and TC Electronics products, just a couple of many. Peavey, Fender and others are also doing this with amp modeling.
  3. Thanks for the info.

    I see that Line6 does do that. I forgot they did things that way. I know they have a user editable piece for the Tonecore series, I need to look into that. I wonder how versatile it is. I was more or less hoping for SPICE that processes signals.

    I though the TC stuff was just standard modeling though.

    It's good to know it's out there though. I really think it will improve modeling effects significantly.
  4. Skrogh


    Jan 28, 2010
    Spice is way too slow for realtime processing.
  5. rsmith601

    rsmith601 Gold Supporting Member

    Apr 14, 2009
    Boston, MA
    President, Source Audio
    Things work well when one is modeling LINEAR circuit elements. Things get much more difficult when one tries to model non-linear behavior.

    There are now many good examples of modeled tube and solid state distortion from many companies (Line 6, TC, Fractal, and....yes....SA).

    Modeling some of the analog compressor circuits is still a bear. The characteristics of how those non-linear circuits behave (and as Skrogh noted making it work in realtime) is not happening yet.
  6. Thanks Roger, I was hoping someone with your experience would respond. I didn't even think about non-linear response. It is a big factor, that's part of the reason the Fuzz Face had a good sound. Modeling it would be much harder since it's less consistent. I'd assume removing non-linearities would be beneficial, but I suppose that's part of the sound. Do you think it would be feasible to code in some of the non-linear functions? Perhaps with some kind of random generator srt to be in a certain range. Of course, the complexity may be excessive there.

    Skrogh, I agree SPICE would be too slow. I was mostly referring to a GUI similar to it. Like, you lay out a schematic on a virtual rather than real circuit board.
  7. rsmith601

    rsmith601 Gold Supporting Member

    Apr 14, 2009
    Boston, MA
    President, Source Audio
    From my point of view is it less about trying to model and more about creating the sound. Some of the old pedals sound great, but not all!! This video tells the story of how we went about addressing this challenge. If you do not get too bored, there is a second part of it too.


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