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Thread: high level question- commercial 'analog' synths compared to audio library

  1. #1

    high level question- commercial 'analog' synths compared to audio library

    I went to the city last week and was chillin at the music stop and I noticed a lot of newer synths like the moog grandmother and the roland SE-02 that were marketed as being analog which confused me. To me an analog synth would have some sort of mechanical or tube oscillator. I am guessing all of these using some sort of digital generation of waves and digital code for manipulating and modulating those waves? if all of this is digital logic when can you call a synthesizer 'analog'?
    Same thing with the eurorack modular synths. Apparently they are passing analog signals between the modules but most of the modules appear to be DSP based. Is that considered analog or digital?
    Hopefully not too off topic for this forum, I am just getting into some FM synthesis on my latest build and this guy was asking me if it was analog or digital and I was not sure how to answer.

    https://hackaday.io/project/168299-c...ynth-version-2

  2. #2
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    That's not really how that works.

    The grandmother and SE-02 are analog synths because they use discreet components and analog ICs to generate the waves, modulations, VCAs, filter signals, and mixing of signals. Digital circuitry/microcontrollers might be used to recall presets and supply control voltages to analog portions of the circuit, but because the signal generation -> filtering -> modulation -> mixing is never digital, these are considered analog synths. Sometimes you find digital/analog hybrid synths where the oscillators are generated digitally (via wavetables), but all further processing is done in the analog domain.

    Not the same thing with eurorack synths. There are many DSP based modules true, but many many more analog modules. You mix and match them up as you please. It's harder to properly labels eurorack as analog/digital because of that. bIt depends which modules you're using. I could have an entirely analog euro system (and have in the past) with not a single digital chip in the entire thing, or I could have a hybrid system (as I do currently).

    FM is something else. It *can* be done analog, and is pretty popular in eurorack in west-coast synth philosophy. I put my dixie II, rubicon, VCA and a wavefolder euro modules together, hook them up in a certain way and I have a pretty powerful FM oscillator (all analog). But it tends to be digital in keyboards because its high parts count and technical complexity. And when you want to start mixing more than one modulator (or "operator"), it just makes more sense to do it digitally. Sheer parts count.

  3. #3
    Quote Originally Posted by bacteria View Post
    That's not really how that works.

    The grandmother and SE-02 are analog synths because they use discreet components and analog ICs to generate the waves, modulations, VCAs, filter signals, and mixing of signals. .
    Super helpful, thanks!

    What sort of integrated circuit would produce a purely analog wave? I just do not know much about it.

  4. #4
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    Quote Originally Posted by colorado_hick View Post
    Super helpful, thanks!

    What sort of integrated circuit would produce a purely analog wave? I just do not know much about it.
    There are so many options!

    A few opamps hooked up together can be set up, roughly speaking, to have a voltage rise at a certain speed, and when it hits a certain point, the voltage descends. If you hook up such a circuit so that it looks, you have a very rough triangle oscillator, though not stable or consistent.

    https://www.eeeguide.com/wp-content/...ing-Op-amp.jpg

    You can make simple oscillators like this more consistent over large frequency ranges with more components, and different ways of achieving the same "stages". Maybe you'd like to generate the square waves another way. Adding analog comparator stages, diode limiters and whatnot will yield sine waves, sawtooth, etc. Add another oscillator to it and you can sync, ringmod, FM, really fun.

    An even more fundamental way of doing this is substituting opamps for discreet transistor circuits. Parts count goes way up though, so I don't think we see it that often.

    Another option is the myriad of "synth parts on a chip" chips. Like the CEM/SSM series. They're essentially custom analog circuits in a chip that are fine-tuned for synths. So instead of needing half a dozen opamps, 4 diodes, 15 caps, several transistors and 40 resistors for a basic square/tri/sine oscillator that has 1-volt-per-octave tracking, you'd only need the one custom chip that has most of that integrated and calibrated, and a dozen external components. When you're an 8-voice analog polysynth manufacterer in the 80s such as korg or rolands, saving this much PCB space and manufacturing cost is extremely appealing. Same goes for filters, VCA's envelopes, all kinds of functions. And good news for DIY, a lot of them are available as clones.

    https://en.wikipedia.org/wiki/CEM_an...M_ICs_they_use

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