MIDI triggering in Propellerhead Reason

In this guide, you'll learn how to use MIDI notes in Reason to trigger LFOs in ShaperBox (NoiseShaper, VolumeShaper, TimeShaper, DriveShaper, FilterShaper Core, CrushShaper, PanShaper, WidthShaper), VolumeShaper 4, PanShaper 1, FilterShaper 3, MidiShaper and PanCake.

When this technique is used, the LFO will play from the beginning every time a MIDI note is received. Thus, the LFO can be triggered in any rhythm you like — sidechain your bassline to a non-4/4 kick drum pattern, for example.

1. Create a virtual MIDI port

Reason cannot route MIDI directly to VST effects, so you will need to install a virtual MIDI port. This is a piece of software that enables MIDI signals to be routed 'behind the scenes', like a virtual MIDI cable. We’ll be using it to plug Reason’s MIDI output back into its MIDI input — a technique called 'MIDI loopback'.


macOS’ built-in IAC driver is all you need for MIDI loopback.

Open the Audio MIDI Setup application, which you can find in the Applications/Utilities folder, or by doing a Spotlight search (⌘-Space) for 'audio midi setup'.

In the Window menu, select 'Show MIDI Window', double-click the IAC Driver and make sure 'Device is online' is checked.


On Windows, you'll need to install free third-party software to provide the virtual MIDI port – for example, LoopMIDI.

2. Enable MIDI Trigger mode

In ShaperBox 1, VolumeShaper 4 or PanShaper 1, select a 'MIDI Triggered' or 'MIDI 1-Shot' triggering mode. In ShaperBox 2, set the MIDI Trigger mode to 'On' or 'On (1-shot)'.

3. Add the EMI device in Reason

In Reason, add an Instruments >> Reason Devices >> External MIDI Instrument (aka EMI) device. Set its output to the virtual MIDI port you set up in Step 1 (eg, 'IAC-driver 1').

4. Add the triggering MIDI notes

On the EMI track, insert MIDI notes in the rhythm with which you want to trigger the Cableguys plugin.

Any note will work, except when ShaperBox or ShaperBox 2's Wave-switching MIDI Trigger option is enabled, in which case only C notes will retrigger the LFO Wave.