Circuitbenders Forum
Circuitbenders Forum => Circuitbending discussion => DIY Synths => Topic started by: jamiewoody on February 03, 2011, 10:53:03 PM
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i know this has been covered before, but please tell me if i have this right...
a synth block diagram is basically:
VCO>LFO>VCF>VCA...yes?
and VCFs are hi-pass, lo-pass, band-pass, band-stop?
also, when hooking up VCFs, is there a concrete way to do it? or is it a matter of taste? i mean in terms of series or parallel. should i think of VCFs similar to pedals on a guitar pedal board?
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The LFO shouldn't be there. The LFO is like an envelope generator in that it produces a signal, in this case probably a control voltage, that modulates parameters of the other sections. Other than that the basic signal flow is correct.
Most synths will have one multimode VCF, as opposed to several separate VCF circuits cascading into each other or running in parallel.
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i feel this would help me to actually LEARN how to build filters, instead of just copying an existing circuit. for some reason, the hands on approach helps me to learn better.
doesn't an lfp basically vibrate the frequencies of the vcf?
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an LFO can 'vibrate' or modulate the frequency of a VCF cutoff, or a VCF resonance amount, or a VCO pitch, or a VCA level, or a VCO waveform shape, or VCO pulse width, or just about anything else you can set up to have a CV input. Thats the wonderful world of modular synthesis!
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If anything, the LFO should go above or below the entire VCO>VCF>VCA, and have an arrow pointing to each stage. :)
Think in terms of synth signal flow, rather than synth logic.
As for parallel vs serial filters, both paths have their benefits and available techniques, I'm always happy to have 2 filters on a synth!
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ah, so the lfo should be parallel!
on the bass pedals, i will have to actually wire switches (heavy stomp style) for each function. but, on my keyboard, since i will be playing it with hands and not feet, a patchbay will prolly be cool! :o ::) ;D
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no , the LFO is NOT in the signal flow . it applys modulation to the modules that are part of the signal flow (vco vcf vca) or indirectly to other modules that modulates modules of the signal flow (others lfo'S, vco'S used as modulator, enveloppes ... )
the audio path (signal flow)
and the control volage connections are two different things but sometimes you can trow an audio signal in a control voltage input and it can give good results
i suggest you read a couple of the articles on this page , that what i do while i drink my morning coffee
http://www.soundonsound.com/sos/allsynthsecrets.htm (http://www.soundonsound.com/sos/allsynthsecrets.htm)
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confusing...that link just had articles on how to make a synth sound like a cowbell....lol
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go way down to the bottom of the page . its a serie of articles that were published monthly. the first 20 articles cover the basics and the later one cover more specific techniques . so go down to part 1 and begin from the start.
i'm somewere around part 26 . i'm not yet to the cowbell chapter
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thanks, i understand now. the LFO is not inseries but parallel...to modulate the VCFs.
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That's the idea. Bear in mind that it could also modulate the oscillator for siren effects, or the VCA for tremolo effects, or even modulate the speed of another LFO which is in turn controlling the VCF cutoff. It's like an automatic knob twiddler. :)
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i guess that is the appeal of a patchbay on a keyboard synth, to experiment with all the elements...ah, cool idea, more than one lfo!
while i am still DREAMING, i am thinking of building a basic vco/vcf/lfo (in no order) synth, but also making the box big enough for upgrades....like output tremolo, ring modulator, etc. this way, i can add more as i learn and at my own pace...
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on my keyboard, i have been wondering how many vcos i should build. should i make one? or several, to handle bass, mids, etc? the keyset i want to use is on a pcb strip with reed switches. it would be too hard to separate the keys.
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Typically the VCOs track the full range of the keyboard. Having more VCOs means you can create more complex sounds, but they should all handle the same frequency range.
One notable exception is the sub oscillators on the Korg Polysix and Roland Junos (and related models) which is a squarewave generated by passing the output of the oscillator into a divide-by-two or divide-by-four circuit.
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I'd say go for two or three oscillators. Three will give a good amount of sound making scope.
When you say one for the bass and one for the mids, do you mean them both to be components of the same sound? This way would make the most sense to me, for example one oscillator at C3, another a fifth above it, and another acting sub oscillator an octave or two below - the sub osc doesn't necessarily need to be a dedicated oscillator, see Gordon's tip on the frequency divider.
As you say, splitting the keyboard would be a bit harder... worth making a monosynth at this stage. I'd be inclined to say build up the basic monosynth you have planned, but make it all patchable for future expansion.
I'm gradually piecing the components together for my own DIY monosynth, but fitting it around all the other projects, a music career, a girlfriend, and necessities like sleep and food isn't easy!
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It's worth looking at offloading some of the duties to a microcontroller, especially if you're using a repurposed "toy keyboard" keybed that is already matrixed.
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actually, nope, i'm not going to use "toy keyboards"....i have decided i hate sensor based things on pcb....i am going to use real reed switch full size keys harvested from a spinet organ! ;-)
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Actually, it's fun to let the VCOs mod the filter cutoff frequency and pitch of other VCOs as well. Running these signals through an envelope (or LFO) to control the amount it affects them over the time of each keypress makes for a more dynamic sound. :)
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reed switches? don't mean to blow my own horn here, but maybe you should check out my blog.. i started modding a Hohner Bass3, which is basically a square wave oscillator (40106) controlled by reed switches. the square wave is then divided down into several suboctaves, and mixed together they form 1 'timbre'.
read more here: http://remork.blogspot.com/search/label/Hohner%20Bass3 (http://remork.blogspot.com/search/label/Hohner%20Bass3)
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Lots of useful suggestions in the thread. I would proceed in as gradual a way possible, with the simplest components at first just to learn things along the way.
I'd start with just a single VCO with a single waveform. Then, I'd do a simple lowpass VCF, not a multi-mode one. Then, I'd add the VCA. At each segment, I'd try to get a potentiometer for minimal control, e.g. just the frequency for the VCF.
This would give me the basic structure of a subtractive synth.
From there, you could explore each segment in more detail approximately like this:
1. VCO:
a. try to make it a multi-waveform one, i.e. it outputs Square or Sawtooth through a switch
b. next try to get both outputs simultaneously through a mixer
c. add more outputs
2. Add an LFO and make it control the VCO
3. Duplicate the VCO design in 1
a. Make VCO2 modulate VCO1 (Frequency)
b. Make VCO1 modulate VCO2 (x-mod)
c. Implement PWM
d. Implement OSC Sync
4. VCF (try to get 2 resonant 12dB filter chips, or two chips with 4 accessible poles, keep the second one for later)
a. Control the Resonance
b. Add Cutoff as LFO destination
c. Add Resonance as LFO destination as a switch
5. Think of a simple Envelope generator here
a. Add that to the Filter Cutoff
b. Add Faders for each Env segment
c. Duplicate the Env and add that to the VCA
From there, you can revisit every segment and improve each. Things that would be helpful:
6. Waveshapers
7. Ways to combine LFOs
8. Getting to Polyphony
9. Split keyboard operation (strive for 4 voice polyphony because then you can play a left-hand bass and a 3-note chord on the right, and that's a great basis for composing already)
10. Add Control Voltage input jacks for destinations and output jacks for sources, so that you can patch at will
11. Simple sequencer
12. Simple matrix modulation
13. Simple Flanger/Chorus/Delay effect
14. Cross-modulation/feedback possibilities with the Effects section and the main synth architecture
15. Implement multi-mode Filter segment
16. MIDI/CV operations
17. Micro-controllers
18. Digital Oscs inputs, e.g. Samples, Wave-Table
Some additional tips:
1. Think it terms of segments (i.e. basic synth architecture blocks). It will help you focus: say you have improved your VCO. Then, it's good to ponder on ways to improve the filter section, etc...
2. Try to read a lot about favourite existing synths and their architecture, find their block diagrams and then the schematics. Take note of particular features and the chips/circuits they use
3. When choosing mod sources/destinations on modifications to existing circuits, keep 'musical' mods, drop others.