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In this article, we will talk about the physical connections of MIDI devices — wired and wireless.

In previous articles, we have written a lot about MIDI messages which are transmitted between devices.
Though originally intended just for use with the MIDI DIN transport as a means to connect two keyboards, MIDI messages are now used inside computers and cell phones to generate music and are transported over any number of professional and consumer interfaces (USB, Bluetooth, Wi‑Fi, FireWire, etc.) to a wide variety of MIDI‑equipped devices. There are many different cables and connectors used to transport MIDI data between them.

Wired connections

• Classic
  MIDI devices are typically connected to each by MIDI cables. All MIDI cables use the same wiring and have the same type of 5‑pin DIN‑type male connector on each end.
  In the past few years, MIDI hardware products have become smaller and smaller, especially since many of them are intended for use with mobile computing devices. But this has caused some issues due to the fact that 5‑pin DIN MIDI plugs are pretty big. Currently many products include a stereo 3.5 mm mini‑jack connector in the product itself, with a breakout cable to a female 5‑pin DIN MIDI connector.
• USB
  Some instruments offer MIDI communication with the computer using a standard USB cable instead of a MIDI cable. This has many advantages – in addition to sending MIDI events, the devices can be powered by the same cable. Also, most operating systems, both desktop ( Windows, MacOS, and Linux) and mobile (iOS and Android), do not require any additional drivers or interfaces. All USB Class Compliant MIDI Devices work in plug&play mode.
• FireWire
  FireWire supports peer‑to‑peer connections which are also common in MIDI systems, but it lacks a connection management standard, so most FireWire MIDI devices end up connected directly to computers instead. As with a USB connections, MIDI devices can be powered via a FireWire cable.
• Ethernet
  This type of connection is based on the same standard as Wi‑Fi. In both cases, MIDI messages are sent over a LAN (wired in this case). There is more information about this protocol below, with a description of the wireless Wi‑Fi connection, because it is much more commonly used.
• Internal
  Many instruments also use MIDI on the inside as a way for one internal component to talk to another. These private conversations happen under‑the‑hood, using internal MIDI wiring you obviously don’t see.

Wireless connections

• Wi‑Fi
  Both Ethernet and Wi‑Fi connections are based on the RTP‑MIDI protocol developed by Apple. It was initially introduced as a part of their operating system, Mac OS X 10.4, in 2005, but now it is completely open and free (no license is needed).
  Compared to serial MIDI connection, RTP‑MIDI includes new features like session management, device synchronization and detection of lost packets, with automatic regeneration of lost data. RTP‑MIDI is compatible with real‑time applications, and supports sample‑accurate synchronization for each MIDI message.
• Bluetooth
  Everything is becoming mobile, and music creation is no exception. There are hundreds of music‑making apps for tablets and smartphones, many of which are equipped with Bluetooth Low Energy (Bluetooth LE or BLE) wireless connections. Though Bluetooth technology is similar to Wi‑Fi in that it cannot always guarantee the timely delivery of MIDI data, in some devices Bluetooth requires less battery power to operate than WiFi, and in most cases will be less likely to encounter interference from other devices (because Bluetooth is designed for short distance communication).
  Interestingly, the first MIDI over BLE implementation was also developed by Apple, which introduced support for this standard in iOS 8 and OS X 10.10 in the summer of 2014.

Both types of wireless communication - Wi‑Fi and BLE - are supported in the iOS mobile app Wah‑Wah Controller, which allows to control instruments not only wirelessly, but also without using your hands or feet.

MIDI Jacks

A typical MIDI device provides MIDI jacks, or “ports”, into which you can plug a MIDI cable’s connector. There are three types of MIDI ports, and a device may offer one, two, or all three, depending on what the device does:

• MIDI IN jack receives MIDI data from some other MIDI device.
• MIDI OUT jack sends MIDI data produced by the device, out to another MIDI device.
• MIDI THRU — a device’s MIDI IN port receives MIDI data and passes it back out unchanged through the MIDI THRU port. Some devices have a “soft THRU.” These devices have no actual MIDI THRU port, but their MIDI OUT port can be set to act as one.

MIDI devices which communicate via USB, FireWire or Ethernet, may not provide MIDI ports as these are forms of two-way MIDI communication.

MIDI Interfaces

MIDI interfaces available on the market are devices which allow to connect many devices (instruments and computers) often based on various MIDI connection standards. Some of them can convert, merge, duplicate, and route MIDI messages.
Be careful of the cheapest ones which almost never implement the full MIDI specification. A common problem with cheap DIN to USB adapters is the lack of support for Realtime messages (i.e. MIDI Clock, which I will write about in one of the next articles).
With a clear conscience, I can recommend iConnectivity devices, e.g. the iConnectMIDI4+.

MIDI Adapters

It is also possible to convert devices which are not compatible with MIDI, e.g. an expression pedal or foot‑switch, into full‑fledged and fully functional MIDI foot controllers that can be connected to a computer via USB using appropriate adapters, e.g. EX2M, FS2M, or E&F2M combining both functionalities.