Why do I need a MIDI loopback application?

Soft Arranger sends MIDI data which your DAW needs to receive. In a physical world outside of a computer this would be similar to a hardware sequencer sending data to a sound module. In the physical world we would connect them both with a MIDI cable. Inside a computer when we want to connect two MIDI applications instead of a MIDI cable we use a loopback application. 

Normally when you plug a MIDI device (a MIDI keyboard, a control surface, a MIDI interface, etc…) to a computer what happens is that a MIDI port is automatically created so that you can connect your applications to it. If you open your DAW and look at the MIDI devices available for connection you should see all your connected devices listed there. 

What the loopback application does is that it allows us to create a virtual device so your computer will think that you have plugged in a new USB device and it will create a MIDI port for it. Once we have a loopback MIDI port both of our applications can connect to it and thus we can create a MIDI connection.

Notice that if for example you open Ableton live and Cubase and you look at the list of MIDI devices in each DAW they won’t see each other so you can’t connect them to each other via MIDI. If you create a loopback MIDI port called “Joe’sPort” for example. Then you would see that Joe’sPort appears in the list of MIDI devices for both applications and you could for example connect the MIDI output of Ableton to the input of Joe’sPort and the MIDI input of Cubase to the MIDI output of Joe’sPort to create a one way MIDI communication.