Master Class – Propellerhead Reason’s CV Secrets
PROPELLERHEAD REASON isn’t just an integrated recording program with multitrack
audio and a suite of built-in instruments and effects—it’s also a giant modular
synthesizer, thanks to an exceptionally versatile patch-cord-based modulation
routing system. Making connections among Reason modules using the rear panel
CV (control voltage) jacks is a great way to add color and excitement to your music.
|Fig. 1. CV connections in Reason are on the modules’ rear panels. The Subtractor synth module has three CV outs and 17 ins. The knobs next to the modulation input jacks can reduce the levels of the incoming signals.
|Fig. 2. The default routing of the Matrix Note and Gate CV outputs to the Sequencer Control inputs on a Subtractor. The unipolar/bipolar switch on the Matrix affects only the Curve CV output.
|Fig. 3. Using track automation clips rather than CV signals will produce identical results, but more editing will likely be needed. Here, the filter resonance of a Subtractor is being swept repeatedly by identical two-measure automation clips to produce an LFO-like effect.
This Master Class explains the basics of Reason’s CV patching, as well as
potential applications; you can download Reason song files that demonstrate many
of the techniques from Electronic Musician’s website (emusician.com). Most of
these concepts work fine with anything from version 4.0 forward, but we’ll also
look at a few of the new CV processing modules that are available as optional Rack
Extension (RE) plug-ins starting with Reason 6.5.
What’s a CV? The CV concept dates back to the early days of analog synthesis.
Control signals were routed from a modulation source to a modulation destination
within a hardware modular instrument by plugging in patch cords. The control
signals were rising and falling electrical voltages—hence the term control voltages.
Because Reason lives inside a computer, its CV signals are streams of digital
numbers—but they work very much the way analog control voltages used to work
(and still do, if you own an analog synth). If you want to be technical, you can call
Reason’s CVs control values.
If you create a Subtractor synth and hit the Tab key, you’ll see its rear panel (Figure 1). There’s only one audio output;
those other 17(!) jacks are for patching CVs. In
Reason, the audio jacks are a bit larger than
CV jacks, but no worries—Reason won’t let you
make connections that wouldn’t work. Many of
the CV inputs have trim pots for scaling back
the amount of signal being received.
The Subtractor’s rear-panel upper-left
corner shows CV inputs labeled Gate and CV.
If you create a Matrix Pattern Sequencer below
the Subtractor, the Matrix’s Note CV output
patches automatically to the Subtractor’s
CV input, while the Matrix Gate CV output
patches to the Subtractor’s Gate input. This
patching suggests an important fact about
Reason’s CVs: While the input and output jacks
are all alike, CV signals are not all alike.
|Fig. 4. For animated wave sequencing, try controlling a Subtractor’s oscillator phase, FM amount, and filter cutoff frequency from three Matrix curves.
|Fig. 5. Three Subtractors have been installed in a Combinator, and their LFO outputs are being used as CV inputs to the Combinator. The CV destinations would then be set up in the Combinator’s Programmer section, as shown in Figure 6.
Gate signals correspond to MIDI NoteOn
messages, and like NoteOns, they contain some
additional information—velocity for an actual
NoteOn, or a level value for a gate CV. The
gate value ranges from 0 to 127. The CV input
in Subtractor’s sequencer control section (as
in other Reason synth modules) corresponds
to the MIDI note number value, which again
ranges from 0 to 127.
The sequencer control CV inputs are
designed to receive notes from the Matrix,
but can usefully receive messages from other
sources. A Redrum or Kong, for instance,
can send a gate signal each time a drum
sound is triggered.
You can patch an LFO from another device
into a gate input; this works perfectly for
triggering notes. However, patching a CV from
anything except the Matrix into the CV (note)
input in the sequencer section probably won’t
give anything useful.
General-purpose CV signals can be either
unipolar (0–127) or bipolar (from –127 to +127).
Some devices, such as the Matrix, have rear-panel
switches for selecting either unipolar or
bipolar mode (see Figure 2). This works with the
Matrix’s curve CV output, not its note or gate
CV outputs. An envelope generator naturally
produces a unipolar signal, because its output is
zero when no envelope is being generated, and
rises while the envelope is happening. LFOs
normally produce bipolar signals—but the mod
generators in Malström, which are most often
used as LFOs, have several unipolar waveforms,
as you can tell by looking closely at the waveform
graphic on the front panel. There are no rules
about whether to use unipolar or bipolar CVs—
use whichever suits your musical needs.
CVs vs. Automation You can automate
any CV-controlled synthesis, effect, or
mixing parameter in a Reason sequencer
track: Just select the track for the device you
want to automate, hit Record, and move the
knob or fader. So why use CV signals rather
For a periodic parameter change, a CV
(perhaps from an LFO or a Matrix) would be
a better choice. You can get the same result
by recording a brief automation clip into the
sequencer and then copying it over and over
down the track, as shown in Figure 3—but if
you later decide you want to change it, you’ll have to erase all of the copies, record a new
clip, and then copy it over and over. Making
a single LFO adjustment is much easier. And
if you want to control several parameters
on different devices in the same way, using
a single CV source and splitting it using a
Spider CV Merger & Splitter module will
often be easier than automating the various
A CV is also ideal if you want to extract one
module’s behavior, and apply it to another. Kong
and Redrum have CV gate outputs from their
individual drum sounds, so every drum generates
a gate that can feed a different module—perhaps
an ECF-42 Envelope Controlled Filter that’s
processing the drum sound. If you change the
drum pattern, the other module will follow right
along with the new pattern.
Still not sure how you’d use a CV? Here are
some ideas to get you started.
Subtractor Oscillator Phase Stepped
rhythmic modulation of the Subtractor
oscillator phase parameter can be a nice
alternative to step modulation of filter cutoff,
as the latter is a bit of a cliché. The Matrix
Curve CV output is ideal for stepped CV
patterns. With this patch, you’ll have to set
the Subtractor oscillator to the – or x setting,
as the o setting doesn’t respond to phase
changes. For more complex patterns, create
three Matrixes and patch their curve outputs
to the Subtractor’s phase, FM amount, and
filter cutoff inputs (see Figure 4). Set each of
the Matrixes to a different pattern length. [file:
Subtractor Versatility Here’s a simple
but useful patch. When using t he front-panel
controls, the Subtractor’s LFOs can each
be routed to only one destination. If you
need to modulate three different Subtractor
parameters from LFO 1 (while LFO 2 is doing
something else), create a Spider CV Merger
& Splitter, flip around to the back panel, and
patch the Subtractor’s LFO 1 output to one
of the Spider’s Split inputs. Now you can
modulate one Subtractor parameter from LFO
1’s front panel button and other parameters
using its CV output. [file: SubtractLFO.reason]
|Fig. 6. The Programmer panel in the Combinator makes almost any parameter in a Reason device available as a destination for CV control. The routings are programmed in the list on the right.
|Fig. 7. To program your own patterns for the Alligator, hook up three Matrix sequencers as shown.
Subtractor’s filter and mod envelopes
have both gate inputs and CV outputs, so
they’re available as general-purpose sources
for envelope CVs. However, these CVs will
only be produced when Subtractor is playing
notes. One way to work with this is to put the
Subtractor, the gate source (perhaps a Redrum
for programmable rhythm patterns), and the
devices that will receive the envelope CVs
all into a Combinator. When the Combinator
receives notes from your keyboard or a
sequencer track, the notes will trigger both
the synth that you want to listen to and the
Subtractor. If you don’t attach the Subtractor’s
audio output to anything, you won’t hear it—
you’ll just be using its envelope generators.
Envelope Following Generating CVs from
within Reason’s own devices is easy—but what
if you want to modulate something in sync with
audio, such as an acoustic drum or electric guitar
track you’ve recorded? Simply feed the audio
through a device that has an envelope follower.
Three Reason devices—the Pulveriser, the
MClass Compressor, and the BV512 Vocoder—
have envelope followers with CV outputs.
In fact, the Vocoder has 16 envelope
followers, so you extract and use different
parts of the frequency spectrum of a complex
audio signal. It also has attack and decay knobs
for smoothing out the envelope or making it
more “spiky.” When using the Vocoder this
way, set its front panel switch to 16-band
mode. Try feeding a drum loop into the
Vocoder and use one or two of the CV outputs
to control parameters on another device, such
as the filter cutoff on a Subtractor playing a
bass drone. Another trick you can play with
this patch is to delay the audio signal using a
DDL-1 before it enters the Vocoder, so the CV
pulses will always be a few sixteenth-notes late
in relation to the audio coming directly from
the drum loop. [files: DrumVocode.reason,
CV Control Over Everything Many of
the parameters in Reason’s devices have no rear-panel CV inputs. Using a Combinator,
however, you can control just about anything
from a CV. The trick is to install the device(s)
you want to modulate in the Combinator.
Patch the CV signals into the Combinator’s
Rotary 1 through Rotary 4 CV inputs if you
want to use a CV to duplicate the function
of a front-panel Rotary knob, or click the
Combinator’s Show Programmer button,
which reveals four more CV inputs on the
rear panel (see Figure 5).
The Programmer’s front panel interface lets
you select any of these inputs as the source for
a modulation routing. This type of patching is
important to advanced Reason programming,
so let’s take a quick look at exactly how to
do it. Referring to Figure 6, the Combinator
Programmer panel lists, in the left column, all
of the devices residing within the Combinator.
When you click on one of these devices to
select it, you will then see a set of ten possible
modulation routings for it on the panel’s right
side. You can choose a source and target for
each routing using drop-down menus, and
then set a minimum and maximum value for
|Fig. 8. The ReVolt CV Processor is an optional add-on. It has handy front-panel data displays and more than 20 CV connections on the rear panel.
This is a great way to control parameters
like envelope attack and decay time from an
external, free-running LFO, so as to change the
articulation from note to note. You can adjust
the amount of CV modulation using the rearpanel
trimpot, or by setting the Programmer’s
Min and Max values. [file: CombinMal.reason]
Unusual Destinations Using a CV to
control a synthesizer’s filter cutoff or oscillator
pitch is an obvious technique, and often useful.
Here are some less obvious CV destinations
that are worth exploring:
The Malström synth has inputs for its
oscillators’ Index and Shift parameters. These
parameters affect the tone colors produced by
Malström’s wavetable-based synthesis.
The Thor synth module has several CV
inputs for its step sequencer. After defining
a 16-step pattern of note pitches, you can
transpose some of the notes, on some
repetitions of the sequence, using a Matrix’s
note CV output. (Set all of the notes to the
bottom octave in the Matrix, as the lowest
notes in this octave produce a transposition
value of zero.) Then use the Matrix Curve
output to add extra gate time to certain notes.
Propellerhead’s new PX7 synthesizer, based
on the classic FM synthesis design of Yamaha’s
DX7, has a CV input for the level of each
operator. In FM synthesis, these inputs will
change the timbre if the operator is a modulator
rather than a carrier. Try patching several of
these to different LFOs, all set to very low levels,
for a tone color that changes over time.
The rhythm patterns in the Alligator Triple
Gate effect are preset, but after deactivating
the front-panel On button, you can easily
attach three Matrix Pattern Sequencers to the
rear-panel gate inputs and create your own
complex, editable rhythms. Controlling the
frequencies of the three Alligator filters from
the curve CV outputs of the Matrixes (Figure
7) will add to the fun. [file: GatorGate.reason]
The Mixer 14:2 is no longer needed for
output mixing and mastering in newer
versions of Reason, because those functions have been taken over by the much more
comprehensive mixing console. But the 14:2
is still very useful as a submixer, and each
channel has CV inputs for level and panning.
Try using these inputs for cross-blending
various signals in a complex lead or pad patch,
or for controlling the amount of return from a
delay line or reverb.
I seldom use the RPG-8 Arpeggiator,
because I prefer to record arpeggiating
patterns myself, one note at a time. But the
RPG-8 has a useful feature: It can transmit
MIDI mod wheel and pitchbend messages as
CVs. This feature lets you use your mod and
pitch wheels to control just about anything
in Reason. You can use the wheels live, or
record your moves to an RPG-8 track in the
sequencer. (It’s also effective to put the devices
you want to control into a Combinator and
then use the Combinator’s Programmer to set
up the modulation.)
CV Processing (Beef Up Your Rack)
The new Rack Extensions implementation in
Reason 6.5 has opened the door not only to
some extremely cool audio effects and third-party
synthesizers, but also to a variety of new
CV processing modules. These devices tend to
be so inexpensive (like, $9 each) that they’ll be
a good investment even if you’re not sure yet
what you’ll use them for. These modules add
significantly to Reason’s creative possibilities.
Reason’s basic device for CV processing
is the Spider CV Merger & Splitter. It does
exactly what its name implies—and not
much more. The merger’s four inputs have
attenuator knobs, so you can mix several CVs at various levels before sending them on to a
single destination; the splitter section has an
inverted output, which is handy if you want
to flip a CV signal from an envelope generator
upside down, so that it drops when a note
starts rather than rising.
If you need more control over CVs, you can
now add the Quadelectra CV Line Processor,
the ReVolt CV Processor (see Figure 8), or
the Volt SH-1 and CB-1 to your rack. Each
of these has its own unique features, and
this is not the place for a feature-by-feature
comparison. All of them are available as 30-
day trial downloads, so you can explore them
for yourself. (Note that the manuals are not
currently available on the Propellerhead
site. You’ll need to use a search engine to
find and download the manuals from the
manufacturers’ own sites.)
As to what might you want to do with a CV
processor, ReVolt can limit the range of a CV
sweep, so that it “maxes out” and has a flat top
when it hits the upper threshold, or never falls
below a floor that you’ve set. This is different
from attenuation, because it affects only the
signal’s highest and/or lowest values. ReVolt
also lets you use one CV to gate another one or
switch between two signals.
The Line Processor and SH-1 can shape a
CV signal in various ways. The SH-1 has two
resonant filters—not for audio, but for the
CV signal itself. Resonance adds fluttering to
the output when the input changes rapidly.
It also has a syncable sample-and-hold for
turning a smooth input into a series of stair-stepped
Propellerhead’s own Pulsar provides a dual LFO with some extremely useful extra
features, such as the ability to modulate one
LFO from the other or sync one to the other.
It also has a simple attack/release envelope
that can control LFO rate and level. Before the
advent of Pulsar, many Reason producers used
a Subtractor as a handy source for extra LFO
CVs, not using its audio output at all.
If you want to generate CVs, you can
also install the Probability CV Trigger and
Probability Drum Trigger from Ochen K.
Both are 16-step randomizing sequencers. I’ve
found the Drum Trigger very useful for adding
occasional extra hits to a drum pattern. [file:
Final Mix Even if it didn’t have CV routings,
Reason would be a very sophisticated music
production platform. The CV implementation,
especially when combined with the new Rack
Extensions for CV processing, pushes it totally
over the top. If you haven’t yet discovered the
power of CV control, get ready to be amazed.
Jim Aikin started at Keyboard in 1975, and
has been writing about music and technology
ever since. His recent books include Csound
Power! from Cengage Learning.