Arduino as midi host

HI all I've got a midi keyboard that has onlya usb port to be connected to a personal computer. I'd like to connect this port to an arduino board and to manage midi signals coming from midi keyboard as if my arduino were a pc. That to say, arduino would receive midi signals and would transmit that signal thru a real midi port. Further arduino could do some processing beforetrasmit midi signals, for example holdin a chord or gatin a chord.

So I would could use my keyboard as master keyboard to drive other sound generators, keyboards with real midi port

Could you give me some hints? I read a lot about arduino or leonardo used as hid but never about host usb.

thanks in advance alex

A 'normal' Arduino board needs a USB host shield. https://www.sparkfun.com/products/9628

The Arduino Due can be USB host itself. http://arduino.cc/en/Reference/USBHost

Are you sure the keyboard has only a USB connector ? Is there some other connection inside it ? If you want to read the USB midi keyboard, you might need a driver, like the driver in Windows. That is not possible on the Arduino. Perhaps the Raspberry Pi can do that, that is like a mini pc with an operating system.