I want to create a really simple Ableton plugin with a GUI. The only functionality I want is taking the keyboard signal and manipulate the midi output (For example, if I press A from keyboard -where it normally plays note in Ableton, I want to midi output C-maj - 3 notes).
I found a library called Juce but it's pretty expensive. The other libraries I found are for advanced stuff like making a synthesiser. What is the best/easiest way to achieve manipulating midi input? Or is low level code required for such task?