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Fundamentals Of Modular
Synthesis
by Gryphon O'Shea
1
Introduction:
I decided to write this document because though there is a plethora of info
available online about modular synthesis, I fi nd that it is very diffi cult 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
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 fi lter, then into the output. envelope 1 controls fi lter cutoff, envelope 2 controls
volume.
3
CHAPTER 1: Control Voltage
First thing is fi rst - 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 fi lter's cutoff (turning a fi lter's cutoff knob
down) will turn down the cutoff frequency of the fi lter, outputting a low passed sound.
Applying more voltage to an LFO frequency (turning LFO Freq knob up) will make the
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.
EVERY CHANGE YOU MAKE ON A
4
SYNTH IS JUST CHANGING A VOLTAGE VALUE
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/output calibrated to send/
receive a voltage that is scaled to pitch intervals of notes. This is how it works: for every
1V received by a 1v/oct 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
specifi c 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-
confi gured 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 fi lter 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
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 amplifi er, so no sound is
produced. When a key is pressed, the gate goes high, immediately outputting a signal
of 5v, telling the amplifi er's gain to turn up by 5v, letting a sound pass through
immediately when the key is pressed, then continues to be amplifi ed 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
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
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
nstead
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-specifi c. 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
specifi c 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 amount,
8
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 specifi ed) 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 fi lter cutoff frequency.) The
input jack on the fi lter module will have a knob next to it labeled "cv amount." This knob
determines how much the LFO will will now effect the fi lter cutoff. When this
cv amount
knob
is all the way down, the LFO voltage will have no effect on the fi lter cutoff. As you
turn it up however, the amount of voltage from the LFO that is let through to the fi lter
cutoff increases, turning the fi lter 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 fi lter 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 fi ngers. 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 fi lter, 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 -> fi lter input,
fi lter 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 fi lter.
Patch an LFO's sine wave output into the cv input for fi lter cutoff. Now, the fi lter cutoff
9
CV knob (not the actual fi lter cutoff knob) will control how much that the LFO will "turn
the knob" of the fi lter 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 fi lter 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 fi lter 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 fi lter 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
