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MIDI RX (Sysex and RX callback)

For easy use, MIDI RX is accessible without coding: MIDI RX Block

Below are some examples of using the MIDI RX callback and the MIDI SysEx RX callback.

Using the MIDI RX Callback in the System Element Setup​

To handle incoming MIDI messages, you need to use the following callback function in the System element's Setup:

self.midirx_cb(self, header, event)

header Parameter​

The header parameter is useful for filtering incoming messages. We typically use header[1] = 13, which means the message is coming from a DAW, synth, or other external gear.

event Table Structure​

  • event[1]: Channel (0–15)
  • event[2]: Command (e.g., CC: 176, Note On: 144)
  • event[3]: Param1 (usually the CC or Note number)
  • event[4]: Param2 (usually the value)

Example: How to Receive Program Change Messages with Encoder​

MIDI RX callback

1. Load the Correct Profile​

  • Load the profile from Profile Cloud: "midi rx program change".

2. Enable Advanced Editing​

  • In the editor (top-right corner), turn OFF Minimalist Mode.
  • Go to:
    • Encoder → Setup
  • You will see the code blocks.

3. Understand the Parameters​

  • parameter == 0
    → corresponds to Program Change (Pgm1) in Ableton.
  • self.cc == 1
    → means the encoder sends on CC 1.

4. Prepare Ableton Live​

  • Open Preferences → MIDI.
  • Enable:
    • ✅ Track
    • ✅ Sync
  • Enable these for the MIDI port connected to Grid.

5. Send Program Change from Ableton​

  1. Create a new MIDI Track.
  2. Create a MIDI Clip.
  3. Start the clip.
  4. Insert Program Change messages:
    • Bank: 1 Sub
    • Programs: 1 / 2 / 3 (or as needed)

6. Set the MIDI Channel (Optional)​

  • In the code: channel == 0

means MIDI Channel 1.

  • Change this value if you want to receive messages on another channel.

Receiving Sysex​

Usually, you have a custom SysEx implementation. You can use this function, which listens to MIDI SysEx messages. From there, you can parse them and, for example, use them to update Element values.

self.sysexrx_cb = function(self, header, sysex)
    print(sysex)
end

Example:

self.sysexrx_cb = function(self, header, sysex)
  -- Convert hex string to bytes
  local bytes = {}
  for hex_byte in sysex:gmatch("%x%x") do
    bytes[#bytes + 1] = tonumber(hex_byte, 16)
  end
  -- Extract data
  local data = {}
  for i = 5, #bytes - 1 do
    data[#data + 1] = bytes[i]
  end
  print("Manufacturer:", bytes[2])
  print("Device ID:", bytes[3])
  print("Command:", bytes[4])
  print("Data bytes:", #data)
  -- Print data
  if #data > 0 then
    for i = 1, #data do
      print("Data[" .. i .. "]:", data[i])
    end
  end
end