CV in Reason: Behind those front panels

RE Shop CV Utilities

Soon after Rack Extensions were made available to Reason users, we’ve seen a clear growth of utility-type devices specifically dealing with Control Voltage (CV for short).

To better understand why that happened, what missing features these devices are trying to cover and how to get the most out of the existing and new devices, there are a few basic principles about CV that beginners in computer-based music production and even experienced DAW users new to Reason need to keep in mind. Even experienced Reason users that dismissed CV as an uninteresting tool may end up getting something out of these basic notions when reading our reviews and tutorials.


So let’s start with the basics by first looking at the “Control” part of “Control Voltage” before getting into any apparently messy wiring.

Controlling Reason’s Rack devices

Different users, with different backgrounds and interests will have different perspectives of what Reason is and will inevitably grasp it in a couple of different ways.

For this tutorial, let’s look at it as a virtual rack of devices usually seen in a studio hardware rack all connected to a Sequencer.


Inspecting the rack view of a Reason song (press F6), you end up seeing rack mounted Instruments and Effects (and other devices), with those front panels full of displays, buttons, switches, sliders and knobs for you to tweak and control.

When playing an electronic or any other instrument going through a chain of effects, you expect to change things, to turn knobs, tweak parameters as part of the performance to add some movement and texture to the notes being played and Reason allows us to do that in various ways, so let’s see what the various methods available are:

GUI i.e. Mouse and Computer Keyboard


You can use your computer keyboard and mouse to tweak, in real-time, all the controls you see in the front panels of each device, just as you would do on equivalent hardware (physical) devices using your hands.


You can also use your computer keyboard or mouse to play the instruments through the On-Screen Piano Keys (press F4 to bring it up).

Remote i.e. Controller Surfaces and Music Keyboards


You can also get closer to the “hardware-feel” by using MIDI Controlling surfaces or Keyboards, getting the same real-time control of what’s on Reason’s virtual rack but with a better haptic feedback only a physical controller can provide.


Both this method, and the GUI method of  interaction can be used to record all the front panel control actions into the song automation lanes as any keyboard playing is recorded as MIDI Note tracks.

Direct MIDI i.e. Advanced MIDI Device


A related 3rd method of control and an exception to this recording capability, happens when you control your rack devices through the Advanced MIDI Device, which bypasses the Sequencer and Remote layer, directly controlling the device to which the Port+Channel is connected to.

Unless you fully understand what this is, the safest way to deal with MIDI Keyboards and Controllers is using Reason’s Remote capabilities through the Control Surfaces list (to check it, go to Edit, Preferences, Control surfaces).

Internal Modulation i.e. Patches


A 4th method relates to Sound or Patch Designing and varies according to each device’s internal capabilities of allowing certain sections – modulation sections – to automatically change other sections of the device. This is known as internal modulation and involves routing modulation sources to modulation targets.

This type of control or parameter “tweaking” happens purely inside the device. The thing to keep in mind here is that it allows another level of automatic changes, usually cyclical or triggered by events like playing a note that affect the timbre of the sound you’re playing without manually changing all the controls (knobs, faders, etc) involved.  If you have some basic sense of synthesis, a good example of what we’re talking about is LFO or Envelope modulation of a filter.  But of course, much more complex internal modulations are also possible.

Manual vs Automated vs Automatic


So as you can see, the first 2 manual methods of tweaking controls can be recorded allowing you to automate them and free you and your attention to other things in the song, like playing it while sound changes are being handled by the Automation lanes in the Sequencer.

The same holds true if the sounds you’re playing have themselves automatic changes (i.e. internal modulation) that happen either through time or whenever some event happens.

What if… ?


What if you need to change the Squash level of a Pulveriser according to the Filter Envelope of a Thor or trigger a Kong kick drum whenever a new slice of a Dr.OctoREX loop starts?

Would it be possible to pass along some of the automatic changes happening inside a device to another device?  ie. to use some of the modulations sources in one device to control a totally different device’s parameters.

You could certainly do that manually, record it or painfully draw that as automation in sequencer lanes but as soon as you change the Thor patch, tweak that Filter Envelope or change the REX Loop being played, all that work you did as an automation won’t change itself automagically.

There’s got to be an easier way to do these things, this kind of automatic control between devices that none of the previous methods allow as easily.  Enter CV!

Control Voltage aka CV


Reason allows a 5th method of changing those device parameters and note playing.

Control Voltage (CV for short) is how one Reason device can modulate other devices using it’s internal modulation sources.

This is how we achieve inter-device control, how to output modulation control from one source device into the input of a target device, and how one rack device can play notes on another.


Flipping the rack (by pressing TAB) to access the back of devices is how Reason allows us the freedom of CV wire routing, just like we’re allowed to do with those thicker audio cables.

This freedom can be a little frightening to the unprepared but it’s a flexibility that turns into a “super-power” when properly mastered and correctly understood.


…and that’s what the next CV tutorials in this series will try to achieve – stay tuned!

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Musically inclined I.T. professional, technically minded Reason user since 2009, with infrequent acts of Sound Designing released in the wild, some captured in Propellerhead Record 1.5, Reason Essentials and Reason 6 Factory Sound Banks as well as in a few Rack Extension factory patch banks. Propellerhead Remote technology coder and enthusiast, having contributed to extending the existing factory Reason maps to new rack devices since 2010.