Arduino Midi Audio Controller

Hello, I want to make a midi controller using my arduino uno i've found a lot of good tutorials explaining how to do it but i don't find any way to send audio buffer to arduino so i can plug a monitor headphone to my controller and sending midi data at the same time. sorry for my english. thanks

but i don't find any way to send audio buffer to arduino so i can plug a monitor headphone to my controller

That is because you can't do that. Audio has nothing to do with MIDI anyway.

Set up the monitor via a USB audio interface. I got one on eBay for like £3 a while ago. Then build your controller with arduino to handle the MIDI side of things.