Fundamentals Of Modular Synthesis. by Gryphon O'Shea

Transcription

1 Fundamentals Of Modular Synthesis by Gryphon O'Shea!1

2 Introduction: I decided to write this document because though there is a plethora of info available online about modular synthesis, I find that it is very difficult for a beginner to start off without proper knowledge of basic terms, processor types, concepts, techniques, and everything else that makes it possible to understand and apply modern synth documentation and discussion to your applicable knowledge base, as well as taking the ball and running with it on your own sound design adventure. I plan on doing my best to describe every fundamental sound design component, technique, etc. in the most comprehensive and applicable and terms that you can understand without having prior knowledge, to provide a ideal starting point for any future independent study. Though I will be covering lots of basic synthesizer terms since it is important to think of them from the ground up to get the most of them in he modular world (by understanding what the are really doing under the hood) it is assumed that you are familiar with synthesis and basic voice structures. I will ned be describing what an LFO/ Envelope is, etc. I may repeat things many times and come across as redundant. This is me trying to drill this stuff into your brain and make sure it sinks in! I may describe the same thing 5 ways, but as this is not an essay written for english class, I think it's better to maybe give 5 descriptions of the same exact function, because if the reader doesn't understand 4 of the function/technique's descriptions, and the 5th just click with them, that is more important to me than the redundancy. Pictures are not drawn to scale. They are dawn out on my ipad to give the reader some visual indication of the function I am describing. Sometimes I am only referring to a waveform's change in amplitude throughout a wave drawing. This does not mean that since I drew the cycles a little closer together that I am saying the frequency has also increased. Please take the drawings in context, and use them as reference for helping you to understand the point at hand.!2

3 A Quick Reference/Preface Patch Though it is assumed that you have basic knowledge of synthesis, I am going to write out a general subtractive monosynth voice patch that should be fairly obvious to those with knowledge, but might help to remove some frustration from the beginning chapters, and to help you to get a sound out of your system to follow along with the concepts of how to patch intuitively. Basic 2 Oscillator Subtractive Synth Patch: CV Keyboard/Sequencer Module CV output -> Oscillator 1&2 1v/oct inputs via Mult Oscillator 1&2 desired waveform outputs -> Mixer Inputs 1&2 Mixer Output -> Filter Input Filter Output -> VCA Input VCA output -> System Output (Speakers/Soundcard/Multitrack Recorder) CV Keyboard/Sequencer Module Gate Output -> Envelope 1&2 Gate Inputs Envelope 1 Output -> Filter Cutoff CV Input Envelope 2 Output -> VCA Input There you have your basic monosynth patch. 2 oscs with levels set by a mixer, go into a filter, then into the output. envelope 1 controls filter cutoff, envelope 2 controls volume.!3

4 CHAPTER 1: Control Voltage First thing is first - Control Voltage. You will no doubt have heard this term everywhere you go when reading up on Modulars. Here is what it is, how it works, and what it is used for: Synthesizers use oscillators to generate a tone, and this is the most fundamental part of a sound. However with just a tone, we have no musicality, as listening to one tone with no motion or change in quality throughout, playing constantly with constant volume, pitch, timbre, etc., and that is useless. Control Voltage (CV from here on out) gives us the ability to control all of this using any circuit that outputs a voltage, and connecting that voltage output to the parameter we wish to control. Consider a keyboard: A keyboard in its most basic sense uses only keys to control its output, and only has 2 factors that determine this: "if" a key is played, (determining whether there is output or not) and "which" key is played (determining the pitch of the output.) what the keys on a synthesizer are doing is actually producing 2 calibrated CVs to convey this information to the sound generating engine - one CV to tell the engine wether a key is pressed or not to generate a sound (a "gate" voltage,) and one tell the oscillators what pitch to play (a calibrated CV.) simply put, a gate is used to turn something on/off and a cv is used to control something's level. Though these are some common cv types, it is worth stating that the voltage on a circuit is synonymous with that parameter's level. When you turn a parameter's knob up, the voltage applied to that parameter's circuit increases, turning that parameter up. Applying more voltage to pitch (turning the pitch knob up) results in a higher pitch. Reducing the voltage applied to a Lowpass filter's cutoff (turning a filter's cutoff knob down) will turn down the cutoff frequency of the filter, outputting a low passed sound. Applying more voltage to an LFO frequency (turning LFO Freq knob up) will make the!4

5 LFO cycle faster, and so on. This is all just VOLTAGE. All a synth does is routes voltage around its circuits to generate musical results. I hope to describe how you can become a voltage wizard in the following text to make any sound you want. 1V/Octave CV 1V/Oct is a common term referring to a cv input calibrated to receive a voltage that is scaled to pitch intervals of notes. This is how it works: for every 1V received by a module, it increases in intervals of 1 octave. Consider a keyboard controlling the pitch of an oscillator: the keyboard is outputting a cv value for each key on the keyboard so that the lowest possible C is calibrated to produce a specific voltage (let's say 1V) and each step produces a 1/12th of this voltage, up to 2V resulting in C1,3V resulting in C2, etc. In a hardwired synthesizer, all of this is pre-configured inside the circuitry, so that pressing the keys will always be routed straight to the oscillator pitch by default. In a modular synthesizer, you have no hardwired connections, so modules with need to track their controls by musical intervals (like oscillators) are given a 1V/oct input to patch the control source (such as a cv keyboard or sequencer) into. In use: note-pitch and filter keytracking inputs jacks are generally labeled as 1V/oct to show that they are calibrated to receive scaled cv as their control input. It means this is where you plug in your pitch CV. The "MIDI Note #" of the cv world. 1V/Hz CV Though 1v/oct is the common standard for modular synthesis nowadays, there are some exceptions to the rule (such as Korg synthesizers) tat use a linear 1V/hz approach to cv tracking. As octave intervals are the result of doubling the frequency of a note (i.e. A0=220hz, A1=440hz, A2=880hz, A3=1760hz, etc) a 1v/oct Oscillator is calibrated in an exponential manner making it so that each volt received tells the oscillate to double the!5

6 frequency for each additional 1V it receives. 1V/hz callibrated modules however produce a liner response in hertz rather than a musical response in notes, so if each 1V = 440hz (A1) on your 1v/hz synthesizer, 2V will produce 880hz (A2) but then 3V will produce 1320hz, falling halfway between A2-A3. So if you plug a 1v/Octave keyboard into a 1V/Hz oscillator, you will get this atonal response as you play up the keys, and the same goes for plugging a 1v/hz keyboard controller into a 1v/oct calibrated osc. In use: if you have an old synthesizer that you wish to incorporate with modern gear, check whether it is 1v/oct or 1v/hz. If it is 1v/hz, you will need a converter (such as the English Tear by The Harvestman) to convert the cv signal from one to the other. 1v/ hz is no longer common, so this is not a huge issue, but should be addressed. Gates & Triggers A gate is a signal that only lives in 2 states: On ("high",) or Off ("Low".) When low, a gate output will put out 0v, having no effect on whatever it is patched into. When it goes high (turns on) it moves immediately from 0v to its full strength (typically 5v or 10v depending on the module) and outputs that until it is turned off again, falling immediately to 0v again. The easiest way to imagine this is again using the keyboard example: when no key is pressed, the gate is low, outputting 0v to the amplifier, so no sound is produced. When a key is pressed, the gate goes high, immediately outputting a signal of 5v, telling the amplifier's gain to turn up by 5v, letting a sound pass through immediately when the key is pressed, then continues to be amplified while the key remains pressed as the gate is "high" (active, producing 5v) and then goes silent once the key is released causing the gate to go "low" (off, outputting 0v.) Of course this is what you get by just patching a gate signal directly into a VCA's level CV input. Modules like envelopes are used to add a shape to a gate, so to utilize an envelope in this example, you can plug a gate output into a an envelope's gate input which will make an envelope begin its ADSR journey (staying at the sustain point as!6

7 long as the gate is high, just as it would on a hardwired keyboard.) and then when the gate goes low, the envelope begins its release stage, dropping back down to 0v at the time set by the Release knob. So, to utilize this envelope to control volume, you would take a Gate generator (such as a keyboard controller, sequencer, anything that outputs gates,) patch its gate output into an envelope generator's gate input, then patch the envelope cv output into the VCA's gain cv input. In use: A gate is a signal used to tell something to turn on by outputting 5v when "high" then when to turn of when outputting 0v when "low." It only lives in the high/low states, and is never in between. Patch it into other modules gate inputs to have control over them being on/off. Patch it into cv inputs to have control over 0v or +5v level control (off to full.) The "MIDI Note On/Off" of the cv world, which can also be patched into anything (not just a VCA) to have turn it up 5v whenever the gate is high. Triggers are very similar to gates in the sense that they are also used to send a +5/+10v signal out to trigger the functions of other modules. The difference between a trigger and a gate is that while a gate stays high while it is held, a trigger is a instantaneous signal (or "pulse" as they are also referred to) which sends a very short +5/10v voltage out, then drops immediately back to 0. Triggers are generally produced by Clock modules (outputting a constant flow of pulses at a set tempo to sync modules) sequencers with a per-step trigger output (to trigger an envelope per step,) keyboards with a trigger output separate from the gate output (so a gate can be used to control one sustained envelope that will not re trigger when playing legato, while a envelope triggered by the Trig output will re-trigger every time a new key is pressed) and as a feature available on some special modules depending on their settings (Eg. EoR trigger on a Makenoise Maths.) In use: Triggers are commonly used to trigger envelopes with no sustain, to send an instantaneous trigger to a module with a triggered function (changing the direction of a sequencer with a "direction" input, for example, or triggering a drum sound on a drum!7

8 module) and for the example stated above when used above when used in collaboration with gates. Note: just like the 1v/hz note there is another for gates. Some old synthesizers use an inverse gate voltage called an S-trig i read of the common standard v-trig used nowadays. If this is the case for your vintage synthesizer, you will need a converter (again, English Tear works) to interface it with standard v-trig gear. Control Voltage for Function Generators Though the most common and simple way to use cv is to control a 1v/oct oscillator via a 1v/oct cv source to play notes, it is probably the least exciting. There are many, many modules in the modular world that are used to create common (LFO/ envelope) cv mod sources, as well as much more complex mod sources and functions which are module-specific. What's more, most parameters on every module have cv inputs to use cv to control them. As I stated in the intro paragraph to this chapter, any parameter's level is equal to the amount of voltage applied to it (by turning its knob, as the simplest example.) This is not very exciting, as you can turn a knob on any synthesizer's parameter's to change their levels. This is where CV Function Generators come in, ad where things start to get really fun. A cv function generator is any module that is used to create moving voltages in a specific shape or pattern that is used to control ("control" voltage!) another parameter. This is where your envelopes, LFOs, and all mod sources come in. A cv is essentially a mod source: it is used to modulate another voltage, whether that is the 1v/oct cv controlling the pitch's voltage producing notes, or the envelope's cv output being used to control the level of the VCA passing audio out to your speakers. The main difference between cv from function generators and 1v/oct cv is that 1v/oct cv is calibrated to control a parameter such as an oscillator's pitch by a set!8

9 amount, resulting in musical note intervals. A cv from a function generator (which will be referred to from here on out as just "cv" and only 1v/oct cv will be specified) let's your control the amount of the cv strength via a cv amount knob at the destination's input. Here is how patching cv works: you take the cv that you want to use to control another parameter (let's any sine wave LFO) and patch its cv output jack into the cv input jack of the parameter you want it to control (let's say filter cutoff frequency.) The input jack on the filter module will have a knob next to it labeled "cv amount." This knob determines how much the LFO will will now effect the filter cutoff. When this cv amount knob is all the way down, the LFO voltage will have no effect on the filter cutoff. As you turn it up however, the amount of voltage from the LFO that is let through to the filter cutoff increases, turning the filter cutoff up and down (in a sine wave shape, as we are modulating it with a sine wave LFO.) since what we are doing is applying a rising and falling voltage to the filter cutoff circuit, we are essentially doing the exact same thing as turning the cutoff knob up and down repeatedly, except that the LFO is doing it for us, rather than manually doing it with our fingers. So with CV and function generator models that produce it, we can essentially "use any module outputting a voltage to turn the knob of any parameter with a cv input." This is the fundamental technique used to program a modular synthesizer. Consider a patch with an oscillator being controlled by a cv keyboard, going into a filter, going into a VCA whose level is being controlled by an envelope, which is being triggered by the cv keyboard's gate: Kbd key -> 1v/oct input on oscillator, sawtooth output from oscillator -> filter input, filter lowpass output -> VCA input Kbd Gate output -> Envelope generator gate input, Envelope output -> VCA cv input This is a very basic synth patch, and the only cv modulation going on is the envelope controlling the shape of the volume. We can make it into a little bit of a more useful synth patch by using the CV output from an LFO to control the cutoff of the filter. Patch an LFO's sine wave output into the cv input for filter cutoff. Now, the filter cutoff!9

10 CV knob (not the actual filter cutoff knob) will control how much that the LFO will "turn the knob" of the filter cutoff back and forth (in the shape of a sine wave.) We can control anything like this - LFOS into VCA to control how much of a VCA's input passes through to its output, envelope to Filter cutoff/resonance etc, LFO into Envelope Generator's Attack, making it so the attack stage becomes faster or slower each time it's triggered as the Attack knob is being turned up and down by the LFO.. Your imagination is the limit. Summary: As all parameter's on a synth module are controlled by voltage (this is what turning the knobs do to parameters - apply/reduce a voltage to turn them up/down) you can use cv from modules to control each other's parameters, essentially having control over the knob of any parameter they are patched into. Standard cv outputs are the "Mod matrix SOURCE" of the cv world, cv inputs are used to make a parameter the "destination" of this mod source, and cv amount knobs are the "mod amount" of this mod path. Note: sometimes a parameter's FM input will be labeled as a FM input. This is seen sometimes in filter modules for the cutoff cv, ad occasionally on other modules. If you see no cv input jack but you do see an FM jack, use this FM jack to input your cv. The reasoning behind this will be explained in the FM sections of the Audio Signals chapter. Mixing Control Voltages & Modules with Multiple CV Inputs Though mixers are usually thought of as a way to mix audio signals going into the same destination, one of the beauties of modular synthesis is that there are very few rules, and both audio signals and cv are voltages, so they can both be patched into the same modules to be effected the same way (though the result is not always useable.) Mixers, however, are extremely useful for mixing cv signals together to control the same parameter. Take filter cutoff for instance - you may want to be able to use an LFO and and envelope to control the cutoff. In this case, since this filter only has one input for cutoff cv, you would stick an LFO and and envelope into the inputs on a mixer module, patch the mixer's output into the cutoff cv input, then use the mixer's level knobs to assign how much of each cv goes through to the output. The overall modulation amount!10

11 is still dependent on the cutoff cv amount knob, but the ratio of the strength envelope and the strength of LFOS that arrive at the cutoff cv input is set on the mixer. This is how mixing cv result: As you can see (hopefully, apologies for the crude drawing,) the solid mix graph represents the mixed cv's effect on the filter cutoff - it is being modulated in the shape of the LFO, while also being modulated in the shape of the envelope (indicated in dotted lines,) making for a more interesting sound which has repetitive movement from the LFO cv, and movement over time from the envelope cv. When a module has 2 cv inputs for one parameter, it has an internal mixer that mixed both of the cv inputs to affect the one parameter, at levels set by the cv amount knobs. Sometimes it will feature a 1v/oct cv input (for things such as filter cutoff, which will track pitch when the filter resonance is self-oscillating) with no cv amount knob, plus a cv input with amount knob. What this means is that the 1v/oct input has a set cv!11

12 amount (calibrated to receive 1v/oct cv and let it affect the parameter at musical 1v/oct intervals, for instance in the self oscillating example I gave, patching a cv keyboard's output into this Jack will result in the self oscillating filter playing the note intervals played on the keyboard. It can also be used for exponential FM - remember, 1v/oct is an exponential calibration as octaves are exponentially increasing hertz -if an audio source is patched here, but we will get into audio rate cv later.) and the 2nd cv input with cv amount knob is meant to be used for modulation cv. Multing: Multing is a way to duplicate one cv signal signal for use with multiple destinations. This is done either with a Mult module, or with Stackables (cables inspired by the banana cables used by Buchla and Serge modules which allow you to stack multiple cable by plugging cables into other cable heads via a socket on the back of the tip.) a Mult module has 4 sockets. Patch your cv into one Jack, and the other 3 Jack will now contain copies of that voltage ready to patch int 3 different cv inputs to modulate 3 different parameters with the same cv. Note: Multing works for cv signal (outputs) only! You cannot use a Mult to give an input 3 jacks. Use a mixer to feed multiple cv's into a single input. Also, regular mults can only accept one cv signal, then the other jacks must be used to patch that signal into other modules' inputs. (There re some exceptions for multifunction mults such as Mutabl Instrumens' Links module.) Study Points & Terminology covered in this chapter What control voltage is What a 1v/oct cv is and what it is used for What a 1v/hz cv is and what it is used for What a Gate is and what it is used for High/Low state of the gate What a Trigger/Pulse is and what it is used for Sustained envelopes vs pinged envelopes What turning a knob is really doing Using standard cv to control modules with other modules How to mix cv Why some parameters have 2 cv inputs Multing a cv to route it to multiple destinations!12

13 Chapter 2: VCAs How to properly think of VCAs Most people coming from a hardwired synthesizer background think of a VCA as the amplification stage of the sound design process, and as a kind of volume control. While this is the most common and basic use of a VCA, this in not how you should think of it, and not what it is. A VCA is something that takes a signal at point A (whatever you patch into the VCA input) and gives you control over how much of that signal is passed through to point B (whatever the VCAS output is plugged into) as determined by the voltage applied to the VCA's gain. Usually a VCA will feature one of more channels, each equipped with an input Jack, a gain knob, a cv input Jack, a cv amount knob, and an output jack. When you plug a signal such as an audio signal into the input and plug the output into a destination (such as the input to your speakers,) the gain knob will apply voltage to the gain circuit (remember, turning a knob just applies voltage!) and the signal will pass through to the output. It is like a dam that blocks the input from flowing into the output, and whatever voltage is present on the gain is the amount of signal that the dam lets through. In this instance, turning the gain knob to apply voltage to the VCA's gain will let a constant stream of audio through to the speakers at the level set by the gain knob. Constant sound. No on/off. Not very useful, as we could just do this with a mixer. But with modular synthesizers, we have this amazing thin called control voltage! So... CVing VCAs Since letting a constant stream of signal through the VCA is not what makes a VCA special, we are going to ignore the boring gain knob which only applies a set!13

14 voltage to the gain circuit. What we're going to focus on is the CV area on the VCA. Let's turn the gain knob all the way back down and focus on the CV input and amount knob of the VCA, as this is far more useful. The CV input is where you can patch a cv in that you want to control the level of gain, as any amount knob (as any cv amount knob does) scales the voltage that this cv applies to the circuit (so if you apply 10v to the CV input and turn the amount knob up 80%, 8V will be applied to the gain circuit.) This lets you use cv to control the amount of signal A reaching signal B. As the simplest example, using the Gate output of a cv keyboard will apply 5V to the gain circuit when a key is pressed and the gate goes high, then immediately go back to 0V letting no signal through when the key is released and the gate goes low. In our patch, this results in no sound output (0v of gain,) to hearing full level output when the gate goes high (5v of gain) to hearing no sound output as soon as the gate goes low (0V.) this is what is happening inside of a hardwired synthesizer when the VCA is set to Gate Mode (a feature on synths such as the Roland SH101.) As this is also pretty boring, using a gate signal to turn the VCA's gain to either +5V or 0V with no movement and no points in between nothing and full, we will instead use a better suited cv source for the job - an Envelope. As we still want the keyboard pressed/unpressed (gate high/low) to determine whether a sound plays or not, we will still use the keyboard's gate output, but to tell the envelope whether to play or not, rather than to tell the VCA gain whether to let signal through or not. For this patch, we will patch the keyboard's gate output into the Envelope Generator's gate input jack to tell it when to play and how long to sustain (as long as the gate is high) and when to release (when the gate goes low) then patch the envelope output into the VCA cv input. We must then turn up the VCA's cv amount knob to set the amount that this envelope will control the gain. All the way up = the envelope's highest point will let maximum signal through, and lesser points will scale the amount down relatively. This is how you use a an envelope to control a VCA to control the level of your audio signal going out into the speakers. Which though incredibly useful, is not extremely exciting, as it is a standard feature on most hardwired synths. It does however give you the option to use any cv generator in your system to control the level of the audio output, which can be cool for drones and that kind of thing. Set the gain knob high so there is some constant sound present, then patch a slow sine wave LFO into the VCA cv input, and turn the cv amount up a little bit to let the LFO slowly make the sound get louder and quieter, giving it some constant movement. That's kind of cool, way more control than a standard hardwired synth.. Anyway, the truly cool part is coming up now!!14

15 VCAing CVs "You can never have too many VCAs!!" This is a frequently quoted sentiment in the modular synth community and leaves some new users thinking "Why? I can't possibly have that many sounds going simultaneously to control the volume of..." Which brings me around to the reason why I opened this chapter the way I did, and why I put a whole chapter aside for VCAs: "A VCA controls how much of ANY signal at point A goes through to ANY destination at point B." And what signals do we like to patch around between points a lot on modular synths? That's right! A VCA's biggest use in a modular synthesizer (and one that really increases your synthesis capabilities exponentially" is to control the amount that a cv goes into the destination that it wants to modulate, and to have cv control over that amount! So what can you do with this? A LOT! Let's go to another simple example: some VCA'd LFO modulation of filter cutoff. When you patch an sine wave LFO into a filter module's cutoff cv input, it makes the cutoff go up and down by an amount set up by the cutoff's cv amount knob. But when we patch the LFOS first into a VCA input, then patch the VCA output into the cutoff cv input, we no have voltage control over how much o that LFO goes into that cutoff cv input, essentially allowing any cv we want to turn that cv amount knob automatically. So... Let's choose an envelope to cv the VCA gain (amount of LFO passing through the VCA to control the filter cutoff.) turn the VCA gain knob down, and turn the VCA cv knob up to the amount of LFO that we want the envelope to let through. This is the result we get:!15

16 As you can see, the LFO has no effect on the filter cutoff until the envelope is gated. Once the envelop starts rising, the envelope' voltage is applied to the VCA's gain circuit, letting more of the LFO through as the envelope goes higher, less of the LFOS through when the envelope decays, and then fading down to 0 passing through (unmodulated cutoff) when the gate controlling the envelope is released. If this envelope is also multed to cv a VCA which is controlling the audio output to the speakers like in our last example, when a key is pressed and the envelope is gated, the amount of LFO filter modulation will fade in an become stronger as the audio fades in and becomes louder, decay as the volume decays, sustain at a constant level of filter modulation when the volume sustains, then fade out along with the volume when the gate goes low and the envelope releases. Another thing you could do with this patch is turn up the VCA's gain knob a little to mix it's constant voltage in with the gain circuit's voltage controlled by the envelope's cv. so use the exact same patch we had, but turn the gain knob up a little bit on the VCA as well. This will make it so that there is constant LFO passing into the filter cv input when the gate is low, and when the gate goes high and the envelope runs, the envelope's voltage adds to the amount of LFO passing through to the filter cutoff. This is the result:!16

17 As you can see, there is a constant gain when no envelope is running, then when a get goes high triggering a envelope, the running envelope adds to the constant level of LFO the VCA was already passing through via the gain knob. Here is an example when another and wave LFO (Let's call it LFO2) is applied to the VCA cv instead of the envelope:!17

18 This illustration only represents effect of the AMOUNT of LFO1 modulating the filter (the frequency remains unchanged from the original LFO at the VCA input) but notice that when the LFO at the VCA cv input (LFO2) goes higher, LFO1 effects the filter cutoff more strongly. This is because when the LFOS is higher and it i CVin the VCA, the VCA's gain circuit is receiving more voltage from LFO2, letting more of LFO1 pass through it into the filter cutoff CV input. MASTER THIS STUFF!!! It is one of the most powerful parts of modular synthesis and vastly expands your modulation capabilities. You can seriously never have too may VCAs - it essentially gives you cv amount control to ANY parameter - even a cv amount knob! VCAs as voltage controlled Mixers Many multi-channel VCAs (modules that feature multiple VCA circuits or "channels" in one module) have a "sum" output, which is essentially a mixer that sums the output of each VCAS together into an equally mixed (all VCAs added together in unity, no level control) sum output. This allows your to take multiple signals, and mix!18

19 them together into a destination, each with independent cv control over how much each signal reaches the destination. This essentially essentially makes the sum jack an output that uses let's the VCA a mixer as described in the CV section, but instead of having only having manually adjustable level controls (which the gain knobs will act as in this situation, as they provide a set level of the VCA input running into the output, just like the level controls on a mixer) you have voltage control over the levels using the cv inputs on each VCA. for example, you can use 3 different audio signals (let's say 3 different waveform outputs of a single oscillator - saw, sine, and square) and you run them into each channel of a 3 channel VCA module with a sum output. Now patch 3 different LFOs (lfo1= sine, 2=square, 3=saw) running at different rates into the cv inputs of these channels. Observe the result:!19

20 Now what you get is all 3 Oscillator outputs running into their destination (usually a filter, then into a VCA, then out into speakers) at levels controlled by these 3 LFOs. So the LFO1 makes osc 1 louder and quieter back and forth in a sine shape, LFO2 makes osc 2 full/off in a square shape, and saw LFO3 makes osc 3 rise from 0 linearly to full then drop back to 0 in a saw shape. And this is all at different rates out of sync, so the levels and combination of each oscillator waveform output will be constantly moving around eachother, layered at different levels at different points, creating a very alive and full sound with 3 layers to it, all moving in different directions at different rates. And this is just with 3 waveforms of the same oscillator playing the same pitch, and modulated only by LFOs. We could have 3 completely different audio sources patched into this VCA's inputs (a full synth sound, a full drumbeat, and a bass drone for instance) and have 3 totally different voltages controlling their levels (LFO, Envelope, and envelope follower for instance) giving us some pretty damn crazy mixing capabilities, all by utilizing a single 3-channel VCA module. And lee in mind you can also do this with CV signals. Running 3 different CVs into one cv input, all having the amount that they pass through to affect that cv input controlled by other CVs... This stuff gets crazy quick. Already we are beyond what most hardware and software synthesizers can do, and we are just scraping the surface on basic use of VCAs. Again... Take your time with this stuff. Try it, experiment with it until you understand it!! It is a vital tool and you won't be taking advantage of having a modular synthesizers until you completely understand using VCAs. This is probably the most important chapter of this whole document, as these techniques give you arguably more control over your sound design than any other module. VCAs are essentially the "Mod AMOUNT control of the modulation matrix of the cv world" with the ability to also give that "amount" a mod source. Study Points & Terminology covered in this chapter What a VCA really does Using VCAs with audio Using cv on VCAs to control amount of signal passing from the VCA input to the VCA output Using VCAs to cv modulate the cv amount of another modulation (processing cv through a VCA)!20

21 Mixing the voltage from a VCA's cv input and gain knob to blend external and constant voltages controlling amount of signal passing through the VCA Using a multi-channel VCA as a voltage controlled audio/cv mixer Chapter 3: Audio Signals in a Modular Synthesizer What is an audio signal, actually? In this chapter, I am going to start addressing audio signals and how the work in a modular system, a lot of which you may not have experienced or considered coming from a hardwired synth background. First, we have to address what an audio signal actually is. An audio signal is actually identical to CV in the sense that it is exactly the same type of signal - a Voltage! When an audio cable sends a sound out to a set of speakers, what it is really doing is sending a voltage down a copper wire, to be amplified and converted into audible sound which is played through he speakers. The the difference between an Oscillator and an LFO is that an oscillator generates a voltage in the shape of a specific waveform with a speed of above 20hz (20 cycles per second, the lowest threshold of perceivable audio to the human ear.) ad LFO is a sub 20hz oscillator that can't be heard, but rather is used to create voltage in the shape of a!21

22 waveform that is used to modulate (virtually turn to knob on) any other parameter. The reason we use different waveform outputs from oscillators is to produce different audible timbres with different harmonic content. The reason we use different waveform outputs from LFOs is to create a voltage which rises and falls in the actual shape of that waveform (sine rises and falls constantly, saw rises to a point then drops immediately to 0V, etc.) to apply a moving voltage (aptly called a cv, as it is used to CONTROL something, not to hear on its own) to a circuit in order to control the level of that parameter in that shape. A 1hz waveform goes through 1 full cycle per second (for instance, it will take 1 second for a 1hz sine wave to move from 0v to +5v down through 0v to -5v, then back up to 0v to complete its full sine wave cycle.) a 5hz LFO will produce 5 cycles in one second, and so on. Since an LFO and an oscillator are both outputting voltages in the shape of waveforms, they are both the SAME THING, just designed to excel at different uses, and dedicated modules usually feature additional parameters useful for timbre manipulation/shape manipulation etc, depending on whether it is a module meant to be listened to, or a module meant to have highly programmable control over other modules' parameter's (oscillator vs LFO.) What this means is that an oscillator can be used as a cv as well as output into a filter/speakers etc as a sound source. The only differences is that rather than slowly modulating a parameter moving it up and down repeatedly like a LFO, an audio source patched into a cv input will turn a knob up and down so fast that the change is not audible as modulation, but completely changes the timbre of the circuit it is modulating. This is known as FM (frequency modulation - modulation at AUDIO rate rather than subsonic CV rate) and is incredibly useful for a lot of deep timbre shaping. An LFO and an oscillator module's frequencies can generally run up/down into each others sub 20hz/20hz+ frequency rates. Imagine a 2hz sine wave LFO cv output into an oscillator's pitch cv input (cv modulation input - not 1v/oct input.) the LFO will make the pitch of the oscillator rise and fall twice or second, resulting in a kind of police siren sound. Now take the frequency knob of the LFO and turn that up slowly. As you turn it higher, the pitch will move up and down faster and faster until about 20hz (out of subsonic cv rate into audio rate,) when it will begin to move up and down so fast that the rises and falls are no longer perceived as such, but more as a buzzy sound, imparting harmonic content and distortion bands as the frequency keeps increasing. This is the result of FMing something, and it is what you get if you plug an audio oscillator's output directly into a parameter's cv input. I use the example of an LFO sweeping into audio range because it is important to understand exactly what a voltage moving at audio rate is doing to the signal it is modulating, and performing this frequency sweep starting from an LFO and rising to audio rates let's you actually hear it. It is also important to know!22

23 that these two are both the same exact signals, just running at different frequencies for different purposes. FM in a Modular System FM = Frequency Modulation, which means modulation turning a parameter up and down many hundreds/thousands of times per second to warp the sound into a new timbre. The most basic form of FM is plugging an oscillator's waveform output into another oscillator's pitch CV input, and turning up the CV amount to modulate the pitch. (FM technically means something else, but this is practical FM in modular synthesis, and is generally how we refer to this technique.) Any parameter can be modulated at audio rate, and though the effect may not be desirable or even audible, you should experiment with using audio rates to modulates plenty of parameters just to see what the effects are like, and what FM is capable of. Again, there are no rules in modular synthesis, and that makes it fun! Generally, pitch, VCA gain (Amplitude Modulation, or AM) and filter cutoff (Filter FM) produce a fairly predictable timbre when you FM them (which you will learn with practice, and which varies depending on both the qualities of the audio/waveform you use as the CV, and the qualities of the signal you will be modulating.) For instance, a square wave FMing a sine wave will sound different from a sine wave FMing a square wave which will sound different from a saw wave FMing a lowpass filter at low resonance which was sound different from a square wave FMing a band pass filter at high resonance.. Etc. FM between oscillators depends on a few factors: the waveform/frequency of the oscillator being used as the modulator, the waveform/frequency of the oscillator being modulated (referred to as the "carrier") and the amount that the carrier is being modulated by the modulator oscillator. Filter FM produces a similar type of effect to pitch FM, which relies on the waveform/frequency of the modulator oscillator, the filter type, and the resonance setting of the filter. Higher resonance sounds tend to produce more harmonic content in interesting peaks when FM'd, while low resonance filter fm ca be used to do more subtle!23

24 buzz, dirt, and grit (though a non resonant filter can still get extremely distorted when FM'd at a strong amount.) if you modulate filter cutoff slowly by hand or with a cv signal on a filter whose resonance is high and who is also being FM'd by an oscillator, you will get some very interesting activity in the harmonics and resonant peak bands, resulting in some weird scary monster throat sounds. AM is again similar but has one unique qualities (again, better to hear it an experiment with it than try to describe it or imagine it on paper.) It relies on the waveform/frequency of the modulator oscillator, and the quality of the sound at the VCA input. What AM is doing is turning the amount that a signal passes through a VCA to the VCA output up and down hundreds/thousands of times, again audibly warping the signal just like any type of audio-rate modulation. Note: This is why some cv input jacks are labeled FM input. A cv input Jack and FM input Jack are essentially the same thing, though sometimes you might have a linear/exponential fm input Jack with special calibration for different calibrations of how much the modulator effects the carrier when the cv/fm amount knob is turned up. Harmonic & Inharmonic FM: The Relationship Between Modulator & Carrier Frequency One thing that remains constant through every type of audio rate modulation type is the pitch & type of the modulator oscillator (again to specify, this is referring to the oscillator that you are patching out into something else's cv input to modulate that parameter at audio rate.) this is because the amount of hz (times the parameter is turned up/down per second) and waveform (the "shape" that it is turned up vs down, for instance equal rise/fall on a triangle wave, turn all the way up linearly with a saw wave then drop immediately to 0, etc) have a huge effect on the resulting sound. The relationship between the modulator frequency and the cutoff frequency actually have the biggest effect on the resulting sounds, as even intervals/ratios of the modulate's pitch and the carrier's pitch will produce more tonal, harmonic sounds, while totally odd, unrelated intervals between the two will produce more atonal "sounds" and "effects" such as clangs, bells, buzzes, etc. both have their uses, and both are valuable.!24

25 If you want an easy way to make your FM sound tonal, here is a quick and easy process: take 2 oscillator, and tune them against each other to a musical interval (for clearest results, tune them to the same frequency, or the same note on different octaves.) now patch one oscillator's output into the other's input, and Mult the same 1v/ oct cv signal (a keyboard cv output, sequencer, anything that will be tell an oscillator what notes to play) to both oscillators' inputs. As the 1v/oct source plays notes into these oscillator's, the will constantly play the same notes, which makes it so that the modulator will bring out the carrier's own harmonic overtones (as they share the same fundamental tone, even a different intervals) and will produce a coherent, musically tonal sound (it will produce actual notes.) If you FM an osc without tracking the 1v/oct on not oscillators from the same source, notes played into FM osc's may result as something completely different from notes, with no discernible interval relations between notes, and different timbres per note played. Also very useable, suited well for percussion, metallic sounds, fx, etc. To achieve these sounds, plug a 1v/oct cv into only the carrier oscillator, and run notes into it. As different notes are played, one the modulator stays at the same frequency while the carrier moves up/down. This means that the ratio relationships between the frequencies of the 2 oscillator's changes per step, and will produce entirely different fm tones at ever different frequency played. Using FM through a VCA FM can be run through a VCA just like any other signal. Connect the modulator signal to a VCA input, connect the VCA output to the carrier's cv input, and use on the VCA to control how much of the modulate signal passes through the VCA to FM the carrier. This lets you have cv control over the amount of FM imparted to a patch, in exactly the same way as you would control something like volume or filter cutoff. Fo instance, to create a buzzy destroyed transient, you could patch a very steep fast envelope with 0 sustain into VCA cv, and this will create a very intense amount of fm buzz/distortion of a split second whenever the envelope is gated, adding some initial strike to your sound. Or you could use along envelope to have the fm slowly fade in whenever the envelope is gated, then slowly fade out when the envelope is released. Or!25

26 mix long envelope's cv output and a LFO cv output in a mixer module, and use the combined output to create a constantly pulsating amount of fm that also rises and falls in the envelope shape whenever the envelope is gated... The possibilities are endless, and this is another great example of making use of a VCA in a way not normally considered in a hardwired synth. Study Points & Terminology covered in this chapter What a an audio signal really is (an audible voltage, the same as cv but at a much higher frequency to be used as an audio output or to FM something, rather than a control voltage which uses its rising and falling shape to control something, turning it up and down) How to use an audio signal as to FM another voltage (parameter level) What AM and filter FM are referring to That some LFOs can run into audio range, and vice versa, allowing you to sweep back & forth between slow cv modulation to audio rate FM. Using FM through a VCA to have cv control over FM amount, useful for producing progressive timbre changes/transients Chapter 4: Common Modules and their Functions!26

27 Now that we have discussed the fundamentals of connections and controls used in modular synthesis, I'm going to take a bit of a look at some common module types that you will encounter in module systems, their basic functions, common cv inputs, and how they differ from their hardwired synth counterparts. Sequencers in a Modular System Though we have used a lot of examples of a cv keyboard to describe most of the initial 1v/oct and gate functions, this was mainly to give you a tangible visual example to easily understand those basic functions. In reality, though it's perfectly possible to play a modular synthesizer with nothing but a cv keyboard, this is not extremely common, as it limits your musical output to wha you ca physically play with your fingers. Modular synthesizers go far beyond this, and are just as much melody/rhythm generators as the are sound generators. The most common way to perform melodies with your synthesizer is with modules called sequencers, and it is much more exciting, as voltage does a much better job controlling sequencer parameter's than it does controlling your fingers' parameters. A standard sequencer module features a way to set a tempo (either via a tempo knob, or via sync to external tempos, as addressed in the upcoming Clock Generators section of this chapter,) a series of programmable step controls (generally a knob for each step, usually 4, 8, or 16 steps) which determine the voltage that the sequencer outputs, depending on which step is currently active, and a reset input (which resets the sequencer to first step whenever it receives a trigger/pulse) A sequencer is programmed by its step controls. When you turn one of its step knobs, you are setting the voltage that the sequencer will output when this step is selected as the active step. The sequencer progresses through the steps on every beat of the selected tempo (or every time it receives a trigger/pulse at the sync input.) so let's say you have a 4 step sequencer running at 120BPM with its division set to quarter 16th notes, and the steps turned to up to output 1V on step 1, 2V on step 2, 3V on step!27

28 3, and 4V on step 4. You want this sequencer to control the notes played by an oscillator, so the first thing you want to do is tune the oscillator to its base pitch without any external voltage applied (Let's say we turn the pitch knob until the oscillator is playing a C1 note), then patch the sequencer's output into the 1v/oct input of an oscillator. Whichever step in currently active will now apply its voltage to the existing voltage on the oscillator's pitch circuit (the voltage that setting the pitch to C1.) so what we end up with when the sequencer is running is a looping progression of C2, C3, C4, C5 (since we are patched into the oscillator's 1v/oct input, each 1V that is added to its internal voltage will result in the oscillator adding one octave to its pitch.) As this is great in theory, how do we turn the sequencer's steps so that they output the exact voltages required to make the oscillator play the musical notes in a scale? Well, this is not humanly possible as voltages are analog and smooth with no stepping in between values, so we use a circuit/module called a quantizer. A quantizer is a circuit that has the exact voltages required to make a 1v/oct-calibrated oscillator play musica note intervals memorized, and will take any voltage that you patch to its input, and output the exact voltage for the closest note to the voltage patched to its input. So say (these numbers are arbitrary, but it is the concept that matters) you sequencer is playing a 1.447V signal which does not fall on an exact note value of a 1v/oct callibrated oscillator. You patch the sequencer output to a quantizer module's input instead of straight into the oscillator. The quantizer knows that a 1v/oct calibration recognizes 1.36V as A1 and 1.5V as A#1. Since the 1.447V is closest to the 1.5V A#, the quantizer outputs a 1.5V cv which you then patch into the oscillator's 1v/oct input, and the oscillator will now play an exact A# (assuming you have tunes its own Pitch knob) rather than the exact voltage of 1.447V from the sequencer, which falls in between notes. A quantizer has many other functions for processing CV, and those will be addressed in a dedicated Quantizers section of the Voltage Processors chapter. Some sequencers have quantized output jacks built into the module, which will always output note quantized voltages, eliminating the need for a dedicated quantizer module. Unquantized sequencer outputs are also useful, as sequencers aren't just for sequencing notes: as a sequencer just outputs cv, you can use it as a rhythmic mod!28