Members ripe Posted April 14, 2009 Members Share Posted April 14, 2009 I have always wondered why there are so few analog synths with voltage control of the filter resonance... this is of course excepting complete MIDI controlled analogs with patch storage, etc. I assume it is because the audio passes directly through the resonance potentiometer, rather than being "controlled" by a resistance? Maybe we could get a list going of what analog filters have external resonance control? Does anyone know how the problem was tackled in these devices? digital potentiometers? resistance ladders? * ebbe und flut* serge VCFQ * ? cheersripe Link to comment Share on other sites More sharing options...
Members The Real MC Posted April 14, 2009 Members Share Posted April 14, 2009 Usually controlled by an OTA, but not always a clean solution as you are inserting an active component in the audio path thus altering the timbre of the resonance. Link to comment Share on other sites More sharing options...
Members soundxplorer Posted April 14, 2009 Members Share Posted April 14, 2009 I assume it is because the audio passes directly through the resonance potentiometer, rather than being "controlled" by a resistance? Hmm? Not sure what you mean by "audio passes directly through the resonance potentiometer". You can think of a resonant filter as an EQ circuit. Sort of. An EQ that "boosts" a narrow band of frequencies right around the Cutoff frequency (the boost being the Resonance).Audio is passing through the EQ circuit. The potentiometers just control aspects of that circuit. There is no audio signal passing through those pots. I'd say most analog synth manufacturers, IF they want to include CV inputs, decide on a handful of what people consider to be the most useful inputs, and control over the filter Frequency is going to be way more useful to most people. Otherwise they would be increasing cost for something that doesn't get much use. The Moog MF-101 has Res CV input. I've never found much of a use for it. Link to comment Share on other sites More sharing options...
Members mate_stubb Posted April 14, 2009 Members Share Posted April 14, 2009 In analog, resonance is caused by a positive feedback loop around the filter. Control it with a pot, and you have manual resonance. Control it with a VCA, and you have voltage controlled resonance. Link to comment Share on other sites More sharing options...
Members ripe Posted April 14, 2009 Author Members Share Posted April 14, 2009 Awesome, thanks for the replies. It makes things a bit clearer. In my performance tweakings, I would say that filter cutoff and resonance have equal importance, but "resonance modulation" (via a true modulation source) would not be as important of a parameter to externalize... cheersripe Link to comment Share on other sites More sharing options...
Members soundxplorer Posted April 14, 2009 Members Share Posted April 14, 2009 Control it with a pot, and you have manual resonance. Control it with a VCA, and you have voltage controlled resonance. VCA? A Voltage Controlled Amplifier? If the synth is completely analog, everything is controlled by voltage. A pot is a variable resistor that controls the amount of voltage passing through it. The question was, which synths have a jack on the back that allow other voltage sources to control the resonance. Link to comment Share on other sites More sharing options...
Members ripe Posted April 14, 2009 Author Members Share Posted April 14, 2009 I think what he meant was that the feedback loop (resonance) is an audio signal that is attenuated by the resonance pot. This could effectively be replaced by a VCA (not the onboard synthesis VCA) to control resonance, because it attenuates the feedback signal. So you would end up with voltage controlled resonance via a VCA. cheersripe Link to comment Share on other sites More sharing options...
Members ElectricPuppy Posted April 14, 2009 Members Share Posted April 14, 2009 I think what he meant was that the feedback loop (resonance) is an audio signal that is attenuated by the resonance pot. This could effectively be replaced by a VCA (not the onboard synthesis VCA) to control resonance, because it attenuates the feedback signal. So you would end up with voltage controlled resonance via a VCA.cheersripe ^ Correct. Link to comment Share on other sites More sharing options...
Members soundxplorer Posted April 14, 2009 Members Share Posted April 14, 2009 I think everyone is throwing around terms that don't quite fit together, without quite understanding what they mean, and making things way more complicated than they need to be. I'm going to leave this thread now, because I feel like I'm on the internet version of Candid Camera. Am I being PUNK'd? Heh. Anyone else? Anyone? Link to comment Share on other sites More sharing options...
Members ripe Posted April 14, 2009 Author Members Share Posted April 14, 2009 Well, I'll freely admit I don't know the exact details. So hopefully this thread will provide some accurate information. Also, I'm sure the details would depend on the specific filter implementation, my only experience comes from 303 (and 303 clone) type filters. cheers ripe Link to comment Share on other sites More sharing options...
Members ElectricPuppy Posted April 14, 2009 Members Share Posted April 14, 2009 I think everyone is throwing around terms that don't quite fit together, without quite understanding what they mean, and making things way more complicated than they need to be.I'm going to leave this thread now, because I feel like I'm on the internet version of Candid Camera. Am I being PUNK'd?Heh.Anyone else? Anyone? Please to explain where you think some terms are being used incorrectly? Looks cricket to me. Link to comment Share on other sites More sharing options...
Members Meatball Fulton Posted April 14, 2009 Members Share Posted April 14, 2009 Why is a good question. One possible answer is that noone cared until acid house came along PAiA 9700 and MFB Kraftzwerg both have CV resonance control despite being the cheapest modulars on the planet. Moog Modular filters didn't, so many of the recreations (like the dotcom ladder filter) don't either. I don't have my PAiA schematics any more to check how they implemented resonance. Link to comment Share on other sites More sharing options...
Members ElectricPuppy Posted April 14, 2009 Members Share Posted April 14, 2009 Why is a good question. One possible answer is that noone cared until acid house came along Truth. And witness the LACK of resonance on late '80s/'90s gear. Link to comment Share on other sites More sharing options...
Members ripe Posted April 14, 2009 Author Members Share Posted April 14, 2009 Looking at some of those Kraftzwerg videos online, it seems like a pretty nice sounding machine... would go real nice with the FR XS, which *doesn't* have CV reso unfortunately. cheers ripe Why is a good question. One possible answer is that noone cared until acid house came along PAiA 9700 and MFB Kraftzwerg both have CV resonance control despite being the cheapest modulars on the planet. Moog Modular filters didn't, so many of the recreations (like the dotcom ladder filter) don't either. I don't have my PAiA schematics any more to check how they implemented resonance. Link to comment Share on other sites More sharing options...
Members Meatball Fulton Posted April 14, 2009 Members Share Posted April 14, 2009 PAiA used an OTA for the filter. It's not much different than the VCF example given in the National Semiconductor data sheet for the LM13700, resonance is controlled by the amplifier bias input. In the PAiA circuit they passively mix the CV jack voltage with the voltage out of the resonance pot. Link to comment Share on other sites More sharing options...
Members ElectricPuppy Posted April 14, 2009 Members Share Posted April 14, 2009 Did I read somewhere that the venerable 3080 OTA is being phased-out by all the semi manufacturers? WTF? How's a hobbiest supposed to play anymore? Link to comment Share on other sites More sharing options...
Members mate_stubb Posted April 14, 2009 Members Share Posted April 14, 2009 VCA? A Voltage Controlled Amplifier? If the synth is completely analog, everything is controlled by voltage. A pot is a variable resistor that controls the amount of voltage passing through it. The question was, which synths have a jack on the back that allow other voltage sources to control the resonance. What I said was correct. Because the feedback path around the filter is an audio signal, you must run it through a VCA in order to control it with a voltage. Whether this control input is made available to the user via an external jack varies. For instance, to control the resonance parameter of a Prophet 5 filter, there is an extra VCA in the circuit. The control voltages to control that resonance are not made available externally, but they DO come from the CPU so that resonance can be controlled from stored presets. Link to comment Share on other sites More sharing options...
Members soundxplorer Posted April 14, 2009 Members Share Posted April 14, 2009 Whether this control input is made available to the user via an external jack varies. Right, that's what I thought the original question was all about. Sorry guys, maybe I don't completely understand the internal workings of a resonance circuit. But still, I thought that no matter how the circuit worked, you were still controlling the amount of resonance with voltage when you turned the knob. The concept that you'd be running an audio signal through the Resonance potentiometer seemed a bit strange to me, but maybe that's how some of the old circuits worked. My bad. Link to comment Share on other sites More sharing options...
Members The Real MC Posted April 14, 2009 Members Share Posted April 14, 2009 Did I read somewhere that the venerable 3080 OTA is being phased-out by all the semi manufacturers? You read correct. They're still around but not recommended for new designs. Hell, even the LM13600 is destined for the hall of unobtanium. WTF? How's a hobbiest supposed to play anymore? Yeah, it's getting tough. Non-SMT ICs are getting scarce. I'm still in the inline world but my next project may have to be SMT. Link to comment Share on other sites More sharing options...
Members ElectricPuppy Posted April 14, 2009 Members Share Posted April 14, 2009 it's getting to the point where we'll have to build opamps from transistors again, but then suffer from mismatches and temperature problems, things these chips solve for us. Feh! Link to comment Share on other sites More sharing options...
Members Heathfinnie Posted April 14, 2009 Members Share Posted April 14, 2009 Roland system 700 does, as does the Matrix-12/Xpander Link to comment Share on other sites More sharing options...
Members Purity_Control Posted April 14, 2009 Members Share Posted April 14, 2009 Possibly a lot of analogs don;t have it because with a lot of filter designs, changing the resonance amount also plays hell with the overall volume of the filter, and the crappness of that may outweigh the benefits of being able to mod the resonance. And while i'm here, Doepfer A121 Multimode filter lets you mod it, A120 'Moog' and A124 'Wasp' filters do not. Link to comment Share on other sites More sharing options...
Members urbanscallywag Posted April 15, 2009 Members Share Posted April 15, 2009 Did I read somewhere that the venerable 3080 OTA is being phased-out by all the semi manufacturers? WTF? How's a hobbiest supposed to play anymore? You must be new here. Link to comment Share on other sites More sharing options...
Members deadvolvo1 Posted April 15, 2009 Members Share Posted April 15, 2009 Modulate it yourself on your average synth by hand and see what happens.....Nothing spectacular. Take a whole bank of filters set at different frequencies and what do you get? An amazing effect such as a vocoder. Thus its an added feature at the added cost of not only $$ but making the fundamental architecture and design more complicated. Can anyone think of anything in the musical instrument world that uses modulating resonance at just one frequency (with very little harmonics) as a key aspect of the sound? Thus I share your frustration, but in a different sense....I would like to see a some synths that employ a bank of multi-mode filters with modulation capabilities that extend beyond just cutoff and resonance. Link to comment Share on other sites More sharing options...
Members urbanscallywag Posted April 15, 2009 Members Share Posted April 15, 2009 I think I remember using VC resonance to push a filter into overdrive which did sound neat. There's an interesting blurb by the Fenix people about why they didn't include VC resonance somewhere. Link to comment Share on other sites More sharing options...
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