This project turns any Raspberry Pi into a USB host MIDI hub. The simplest case is to plug two USB MIDI devices into the MIDI hub. The Pi hub automatically routes MIDI IN to MIDI OUT of the two USB MIDI devices. No user intervention is required. Once setup, the MIDI hub is as easy to use as an Ethernet hub/switch. For example, plug in a guitar amp/effects box and a MIDI stompbox controller. If DIN interfaces are needed, there are many USB MIDI to DIN cables.
Linux supports USB MIDI devices but user intervention is required to patch MIDI IN to MIDI OUT. This project automatically detects and cross connects MIDI IN to MIDI OUT for all MIDI devices it finds.
In addition, ipMIDI is supported for all USB MIDI devices so MIDI devices may be connected to other computers or other MIDI hubs. To run ipMIDI on Mac or Windows see https://www.nerds.de/en/ipmidi.html.
Two Raspberry Pi boards running the this project, communicate over Ethernet so MIDI devices on both boards are connected. A simple case is to plug a MIDI keyboard into midihub-A and a MIDI synth into midihub-B. Connect the midihubs to a Ethernet hub or switch. multimidicast moves MIDI over UDP multicast over Ethernet. Ethernet cables may be much longer than USB or MIDI cables so two or more midi hubs may be used a MIDI over Ethernet extenders.
Do not using using WiFi because it adds delays and packet loss.
https://github.com/schuyberg/rpi-midi-hub
https://m635j520.blogspot.com/2017/01/using-raspberry-pi-as-midi-usb5-pin.html
https://llg.cubic.org/tools/multimidicast/
The easiest way to install is to download midihub.run to the Raspberry Pi then run it.
$ sudo sh midihub.run
This will extract and install all the required files. The other files are only required if you want to change the default behavior or settings.