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Master Class – Propellerhead Reason’s CV Secrets

April 16, 2013

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.
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.

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 ( 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 than automation?

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 parameters separately.

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: OscPhaseMod.reason]

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. [file: SubEnvelopes.reason]

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, EnvelopeFollow.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 the modulation.

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. [file: ThorSeqXpose.reason]

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 values.

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: GatorGate.reason]

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.

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