How to send LED feedback to an input via Reactions

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This guide shows how to use a reaction to control an LED on your MIDI controller — turning it on when playback starts in Ableton Live and off when playback stops.

More details: How Reactions work

The article assumes that:

  • you have already configured CSS settings menu correctly.
  • You have added and opened a script.
  • You have attached a controller template to the script and it contains at least 1 MIDI input which you can use to send LED feedback to (for this example we have a button configured named button 32 which has an LED that can be turned on/off and have its color set).

Create a New Reaction

  1. In the Script Panel, add a new Reaction from the mapping type menu.
  2. Name it something descriptive, such as playback LED On off.
  3. Leave the Mode set to the global mode.

Add a Listener for Playback Status

  1. Open the reaction’s settings menu and scroll to the Listeners section.
  2. Add a listener for the event: Live Object Model > Song > Song is playing.
  • This will trigger the reaction every time playback starts OR stops in Ableton Live.

Use Conditions to Filter Playback States

Next, we only want the LED action to trigger when playback starts, not every time the listener fires.

  1. In the Action Block, open the Conditions section.
  2. Add the condition:
    live object model > Song > Song is playing → is equal to → true
  3. Add a new action:
    Send MIDI velocity value to input
  • Input: Button 32
  • Velocity value: 127
  1. Save the reaction and generate the script into Ableton.
  2. Reload the MIDI Remote Script.

Now, when playback starts, the LED on Button 32 turns on.

Turn Off the LED When Playback Stops

To turn the LED off when playback stops:

  1. Duplicate the existing Action Block.
  2. In the new block:
  • Change the condition to:
    Song is playing → is equal to → false
  • In the Action, change the MIDI velocity value being sent to: 0.
  1. Save the changes, generate the script, and reload it in Ableton.

When playback is stopped, the LED now turns off.

Name the Action Blocks

To make the reaction easier to manage in future:

  1. Rename the first action block to: If playback started, turn LED on
  2. Rename the second action block to: If playback stopped, turn LED off