You can connect a MIDI keyboard to your computer to play software instrument patches or to use with external MIDI devices such as synthesizers or sound modules.
When you connect a device with MIDI In and MIDI Out ports, be sure to connect the MIDI Out port to a MIDI In port on a MIDI interface, and connect the MIDI In port on the keyboard to a MIDI Out port on the MIDI interface using MIDI cables.
Do one of the following:
For keyboard controllers without tone generators: You only need to connect the MIDI Out port of the keyboard to a MIDI In port on your MIDI interface, using a MIDI cable.
For keyboards with tone generators: You should also connect the MIDI Out port of the MIDI interface to the keyboard MIDI In port. If your MIDI interface offers more than one MIDI output, connect any other tone generators (or other MIDI devices, such as control surfaces that require bidirectional MIDI communication) to these.
If your MIDI interface has a single MIDI output: You need to connect the MIDI In of the second tone generator to the keyboard MIDI Thru port. A third device can be connected to the MIDI Thru port of the second unit, and so on.
The MIDI Thru port replicates the signals coming into the MIDI In port of the device. It is preferable to use a direct connection from the computer MIDI Out port to a device, rather than chaining too many units, one after the other. Doing so can cause timing problems in the chain, if numerous MIDI commands are sent quickly. This is due to the slight delays introduced by each MIDI In to MIDI Thru transaction. As such, a multi input/output MIDI interface is recommended in studios with several MIDI tone generators and controllers.