Any pitch signal from any source.
To get the signal into the arduino you will need extra hardware. For a MIDI you will need an interface. This shows MIDI being channelled to solenoidal but the could easily be LEDs.
http://www.thebox.myzen.co.uk/Hardware/Glockenspiel.html
Where as to input audio you need hardware something like this:-
http://interface.khm.de/index.php/labor/experimente/arduino-realtime-audio-processing/
For a microphone you need an amplifier in front of the audio input circuitry.