As I get lured back into eurocrack land, it's possibly time I finished this off. Can't remember when I started it but several years ago. Presumably it was intended for something but a (very) quick scan shows I probably tossed it off in a few spare moments. I don't know if it's useful or not, see what you think:
analogue
modular synths: a starter's guide
Getting
started with a modular can be a daunting thing and if you want to
make some noises quickly, hopefully this little, quickly-penned guide
will help describe the important connections, the modules, the
acronyms. It is neither complete nor exhaustive but could grow as
(if) more ideas and tips occur.
So
what's a modular synth anyway? A scary panel full of knobs and wires,
typically, but it's only when you break them down into individual
synthesizer modules with their specific functions and connections
that it starts to make sense. Maybe there will be a better answer to
this later or maybe it'll dissolve into philosophical pap, who knows?
Anyway,
a modular synth is one in which no connections are made between
the various synth components, the exception to this being some modulars with MIDI
interfaces and pre-wired connections - usually for the VCOs and
envelopes.
A
semi-modular synth (e.g. Korg MS20) is one where the most common patching is made
internally so you can make a noise without cables. There are patch
points too, so you can change the signal flow to a greater or lesser
extent depending on the synth.
The
most common terms
VCO
Voltage
Controlled Oscillator
- sometimes you'll hear of a DCO too, which is a Digitally Controlled
Oscillator. This is still analogue but with a digital clock
controlling tuning and probably not relevant to modulars.
The voltage control bit just means that voltage is used to set the
pitch so you can play it conventionally. Other oscillator terms that
come to mind include VCDO (Voltage Controlled Digital Oscillator) as
found in the Digisound modular.
The
VCO, often called simply the oscillator, is the heart of an analogue
synth and typically features a number of waveforms - ideally you'll
have sawtooth, square, triangle and, if you're lucky, sine. Of these
the square wave may be the only one whose pulse width is variable but
on some synths the other waveforms might allow this too. We'll look
at what you can do with pulse width a little later. Hopefully all
waveforms should be available simultaneously so you can pipe them
around your modular freely.
An
important point to remember early on is that modulars typically have
two types of signal - audio and control voltage. Some modulars even
suggest these should be treated separately while in other modulars
that idea is frowned upon. Although oscillators, noise generators
etc. are audio signals, they should still be candidates for sticking into voltage
control inputs, as we'll see.
To
start with, if you connect any of these waveforms straight to your
mixer or soundcard with no voltage control present, you'll hear a
constant tone. The sawtooth is the richest, most full-sounding
waveform and very popular in subtractive synthesis (i.e. synthesis
where you use a filter to remove harmonics). The square wave is more
hollow-sounding and contains only the odd-numbered harmonics. If
there's a pulse width control, adjusting this will change the sound,
gradually becoming a thin, nasal-like pulse. Tonally the transition
is roughly like a morph between a clarinet and oboe. Your VCO should have a
voltage input for pulse width and this can be used to simulate the
action of moving the knobs using a voltage source such as an LFO or
EG.
Drones
are all very well but sooner or later you'll want to play the VCO
from a keyboard or sequencer. For this a CV (Control Voltage) input is required. A VCO
will typically have a couple of voltage inputs at least, and if not a
mixer module will come in handy to mix voltages together. Initially
you'll connect the CV signal taken either from a MIDI interface or
from a CV keyboard - a CV derived from note pitch. Most modulars
these days are 1V/Octave meaning that for every volt supplied the
oscillator increases in pitch by one octave. If your modular has a
voltmeter you can even see this and get a feel for what's going on.
Your
VCO will probably have some CV inputs with an adjacent knob for "CV
amount". While not usually desirable for conventional keyboard
pitch, this is useful for other modulation types - for example if you
are modulating pitch by an LFO to obtain vibrato. The mod amount knob
or CV amount knob, whatever, is used to bring in the vibrato once the
LFO patch connection is made. When you start getting more advanced
you might use an envelope and VCA to fade in the modulation
automatically...
A
VCO might have octave switches, possibly labelled as in organ pipe
footages where a 16' pipe is an octave below an 8' pipe. Some have a
simpler octave up or down switch and some have none at all, or a
large frequency control, hopefully with a fine tune also. An
oscillator can also be synchronised to another - check if you have a
sync input. If so, connecting the output of a second VCO (a square
wave is typically ideal for synchronisation due to the hard edge of
its waveform but experiment with others) will cause the synced
oscillator to restart in line with the master. Here a diagram would
help but for now try it out and then experiment by changing the pitch
of the synced oscillator manually. If you like the sound, you'll
probably already be thinking about connecting a modulation source to
the oscillator's pitch to simulate your knob turning automatically.
If so you're getting the idea why modulars are so darn addictive!
VCF
The
Voltage Controlled Filter
is a key component of subtractive synthesis and many different types
are available to modular owners. A typical filter works by removing
some of the harmonics from your VCO waveforms and also emphasising
some of them at the cutoff point. The two main controls to achieve
this are cutoff frequency and resonance, the latter also known as Q
or emphasis - and probably even wackier things too. Filters are a big
subject so we'll look at them in more detail later but for now it's
enough to think of some of the most common sorts, which are low pass,
high pass and band pass. The names indicate the type of filtering
done - the low pass filter gradually filters out all but the lowest
harmonics. If you have a filter with these three modes it's sometimes
referred to as a multimode filter. Try out each and see what the
differences are.
If
starting with a pure waveform such as a sinewave you shouldn't hear much difference since a sine contains only the fundamental and no
harmonics. However, depending on the filter design and the resonance
amount, you may hear something change. This is because analogue
filters tend to introduce distortion - often almost imperceptible,
but when the input signal level is high the resulting overdrive can
be interesting. Sometimes you might even use an attenuator to boost
your signal in order to deliberately overdrive inputs. The Minimoog
Model D has an external input to the filter and if you routed its own
headphone output back into the filter, a classic Moog overdrive was
the result. Don't try this on a Voyager unless you're prepared for
disappointment though! OK, I digress.
Most
filters include voltage control over the cutoff frequency - so are
prime candidates for envelope, LFO or keyboard voltage control, to
name the obvious three usually included in hardwired synths. Keyboard
voltage is just another term for the pitch CV used to drive an
oscillator in tune. Some filters allow voltage control over resonance
and some even give you the individual outputs of each filter pole.
Ah, poles. Let's get to them later, no point getting bogged down in
details yet.
VCA
Voltage
Controlled Amplifier
- often used as the final output stage. In common with the filter,
the VCA's output is typically shaped by an envelope - so look for a
CV input to make the connection. Some VCAs have a gain control that
raises their level without needing an envelope - this should be fully
down if the envelope is used or there will be a scratching of heads.
As with many modules there should be several inputs for signals,
several for control voltages and at least one output, possibly a
couple of duplicated outputs. There may also be linear or exponential
inputs for the control voltages. We'll look at the difference in a
bit.
LFO
Low
Frequency Oscillator,
sometimes also known as a Modulation Generator (MG), by Korg anyway.
It is very like a VCO, in fact some are also voltage controlled but
the simplest ones don't offer this. It's an oscillator but if you
connect to a sound system, the chances are all you'll hear is a
series of pops. It's low, see. At its highest frequencies you should
hear a tone but this depends on the range of the LFO. The lower and
slower it goes, the longer you have to gradually open a filter or
sweep oscillator pitch. The faster it goes the more strange, atonal
stuff you get as you reach audio-level modulation.
An
LFO should have the same waveforms as a VCO, some might even include
sample and hold - or this could be available as a separate module
(we'll talk about it later as if it was). Connect the various
waveforms to your VCO and hear the difference. There's typically a
visual aid to the speed in the form of an LED. You want lots of LEDs
in your modular, no harm admitting it. If you are lucky enough to
have a voltage input, you can use other modulation sources, maybe a
second LFO, to vary the LFO speed.
ADSR
Attack,
Decay, Sustain, Release - the traditional 4-stage envelope used to
shape the level, the filter etc. Other envelopes are possible, such
as the simpler AR or AD envelopes sometimes seen and even complex
multi-stage envelopes can be found or VC-ADSR where voltage is used
to modify each envelope stage - lots of fun!
I
think the name is pretty self-explanatory and each stage easy to
understand without me going on about it. One thing that often
confuses people is that an envelope is essentially a slew generator -
it takes a certain time to reach its maximum voltage (attack time),
then if you keep the gate open takes time to decay to the sustain
level. Finally when you release the key, the gate ends and the
release phase kicks in, here it takes time to reach zero. As these
voltages are held in capacitors, a new gate played during the release
phase does not start from zero (a sin committed by lots of software
envelopes) but from the current voltage. It would take extra
circuitry to discharge the voltage at this point - but almost nobody
does this because it sounds shit when you do it. Not that this is, in
any way, a hobby horse of mine.
Envelopes
are triggered by a Gate signal - this is a voltage that remains on
until a key is released. They may also be triggered by a regular
pulse, say a square wave from an LFO or the clock signal from a
sequencer. The gate signal is the traditional output of a CV keyboard
or MIDI/CV convertor. Other terms you might hear are single or multi
triggering - this is usually the property of the keyboard itself.
Single triggering (e.g. the Minimoog Model D) allows smooth legato
playing, envelopes are not retriggered if you play legato. A multi
triggering synth (e.g. the ARP Odyssey) retriggers the envelopes for
every new note, regardless of the nuances of playing. Both have their
values of course and it's only flowery hippy types who always play
legato, isn't it?
EG
Envelope
Generator - another name for ADSR, typically.
Patches, patch
cords, patching, Apaches
You'll
have heard the term patch to mean a complete synth sound or program
and patch cords are just the bits of wire used to connect diffferent
modules together. With a modular synth you can make connections that
never occurred to anyone else and therefore never appear on a fixed
architecture synth. Whether you can remember what you did later is
another matter but that's part of the adventure. Digital cameras are
handy to "store" your patches made with a modular.
Ring
Modulator
A
module that takes two signals and outputs their sum and difference
combined. I think that explanation manages to make the ring mod sound
boring - but it isn't. You should experiment with sending two sine
waves (it's easier to hear what's happening with sines) at different
frequencies and hear the bell-like tones that result. Later you'll
send more complex waveforms but for now, the ring mod is not just
used for Dalek voices, OK?
What,
you really want to create a Dalek voice? You'll need a way to get
your voice in and combine it with a sine wave, its speed adjusted
until it sounds Daleky. I may flesh out this explanation if
necessary.
Envelope
Follower
It
strikes me that mention of external processing brings up the Envelope
Follower. This creates an envelope shape from an audio signal, so
it's very useful for external stuff. Vocoders use them to control
band pass filters, the more of these the more you can understand
what's being said. Not sure how I got onto that.
CV
Control
Voltage - voltage sources include envelopes, LFOs, VCOs, sequencers,
keyboards, joysticks, armadillos and aardvarks. Voltage is where it's
at and you should be aware of the voltage requirements for each
module, each input. If combining different modulars, there could be
large differences between the expected voltages, some might trigger
an envelope on a change between 0 and +5V, another envelope might sit
quietly until it is poked with +10V, for example.
PWM
Pulse
Width Modulation
You
remember twiddling the pulse width control manually? Well, with a
voltage input you can get an LFO to do it for you. Or another source.
If your VCO has a variable sawtooth wave, this gives an entirely
different sound to varying the width of a square wave. Check it out.
Faster PWM is commonly used as a source of rich, string-like patches.
Portamento/Glide/Slew
These
terms are often used interchangeably and the process is similar to
basic low pass filtering. Feed in a fast, complex LFO and a slew
generator will smooth it off, send in notes from a keyboard and hear
the differences between notes blur, you get the idea.
Linear/Exponential
these
are terms that are often used to describe the shape of an envelope
stage but apply more widely too. If an envelope has a linear attack
it rises steadily and predictably. An exponential curve sounds and
feels more natural and some synths even offer variations on the
shape, positive or negative curves and so on. For fast sequencer
pieces, an exponential curve on the filter envelope decay is
instantly recognisable and if you have a linear decay you sometimes
have to combine to two envelopes with two speeds of decay to simulate
this. Again, a diagram is in order.
Sequencer
An
analogue sequencer is a joy to behold, especially for the LED-fixated
(i.e. all of us). It consists of at least one row of knobs, each
sending a voltage. An input clock is used to step through the
sequence and each voltage is sent as the step is reached - simple.
Sequencers vary but some allow different directions to be selected
for each row, steps to be skipped, input voltages to transpose the
sequence and so on. Some sequencers can be clocked at audio speeds,
generating an audio waveform - think of this like an LFO running very
fast and into the audio range. I can either write a short amount
about analogue sequencers or a lot - better I write a short amount I
think.
CV
Mixer
You
know what an audio mixer is, a CV mixer might well be the same thing
depending on the modular manufacturer. Mixing voltages lets you feed
more complex signals into a single input plus you can get voltage
controlled mixers too in which a voltage source controls the levels.
This in turn opens up the possibilities for automated mixing,
panning, morphing between audio sources or voltage sources. Sky,
limit, that sort of thing.
Noise
Noise
- assuming you've watched X-Factor, you know what noise is. It
appears in different colours: white, red, brown and so on. White
noise contains an even mix of all frequencies while pink noise has
more emphasis on lower frequencies. Brown is lower still, blue higher
and so on. Noise makes a great modulation source as well as an audio
source for whooshes, surf, spacey wind and whatnot. It's an ideal
source for a sample and hold module to sample and hold...
Oh,
and sampled noise is rarely as good because it's not random and quite
often you can hear the loop.
Sample
and Hold
If
you feed noise into a sample and hold module, oh you need to clock it
too so the module knows how often to sample, you get a random voltage
output. You can feed it different signals too, standard waveforms and
mixed waveforms, if total randomness isn't your thing.
Multis or
Multiples
Some
modulars have banana jacks where you can stack connections on top of
each other. The rest have multiples, a line of jacks in series that
allow you to trigger multiple envelopes from a single source and
generally connect more inputs and outputs than you usually could. One
issue that is worth noting is multiples are not active or buffered.
So if you're using them in applications where precision is important,
such as oscillator CV input, you might notice some of that analogue
magic, reduced range. It depends on your modular, the number of
connections, the impedence and probably other stuff like solar
prominences, atmospheric neutrinoes and celebrity tweets.
Joystick
Distortion/Waveshaping
Quantization
BBD
modules
Bit
Crunching
Spring
Reverb
Ribbon
Controllers
Fixed
Filter Bank
Theremin
Voltage/Gate,
Trigger Delays
MIDI
A
serial interface invented in 1756 designed so that musicians could
mime effectively on stage. Superceded in 1822 by the Laptop.
(and here's my most recent module)
