notes
To connect the Sparkfun MIDI shield, all you need connect is rx, tx, gnd, and 5v
Here is documentation for MIDI library:
http://arduinomidilib.sourceforge.net/a00001.html
Midi thru is enabled by default and can be disabled by MIDI.turnThruOff()
There were problems running MIDI library on an arduino UNO with the USB cable hooked up. So I’m not sure what interaction is happening with the Serial comm stuff in that case, but everything works fine with external power source.
(Update) tried running the shield with minimal connection as above and had no problem using USB power connection.
MIDI out via USB
cable converter:
http://shiftmore.blogspot.com/2010/01/quick-and-dirty-arduino-midi-over-usb.html
Midi In via USB Host shield (for MIDI devices that normally hook into a computer via USB)
http://www.circuitsathome.com/mcu/interfacing-midi-devices-with-arduino-using-usb-host-shield
http://www.circuitsathome.com/products-page/arduino-shields/usb-host-shield-2-0-for-arduino/