MIDI Thru is a lightweight application that helps link MIDI inputs with the MIDI outputs connected to your computer. Residing in the menu bar, the app comes in quite handy when you only want to run your MIDI keyboards and your MIDI modules. MIDI Thru, or MIDI Through, is a MIDI device connection protocol that passes on an exact version of the information present at your device’s MIDI In. This is different from MIDI Out that could at times pass on the input’s copy, but typically has other data on it created by the equipment in question.