There are many ways to do MIDI. This article will break these down into the various methods of connecting multiple MIDI devices.
IDAM - Inter-Device Audio and Music
If you're looking to connect your iPad or iPhone to a Mac computer, look no further than your humble sync/charge cord that you use to charge. Simple plug your device into your Mac using a USB port. Then open a Finder window on your Mac and choose Applications > Utilities > Audio MIDI Setup. In the Window menu, ensure that you are showing the Audio Devices window. Your iOS/iPadOS device will appear on the left side of that screen with an Enable button. Click on the enable button to enable IDAM. This will transmit MIDI between the connected device and your Mac while also charging. Learn more about IDAM on the Apple website.
MIDI is best known for its "5-DIN pin" cables that have transmitted music in digital form since 1984. One of the design concepts of MIDI was the ability to "daisy chain" devices together. This works in a fashion similar to traditional plumbing where one line was used to feed multiple water-consuming devices. In MIDI you chain devices together by plugging in a cable into the "IN" port of the MIDI device and then coming out the "OUT" port to connect to another "IN" port of another device. This can then be connected to a host computer for sending and receiving MIDI through the chain. Of course if you are using an iOS device, you'll need a MIDI adapter to connect to the port on your iPad or iPhone.
The system is simple to understand and works for basic and some advanced situations. However it presents an issue with routing signals as each MIDI device may choose to alter the MIDI events as they are passed. For this reason, some MIDI instruments include a third, "THRU" port which passes the MIDI directly around the chain without alteration. Other devices may offer this as an option for the "OUT" port. These setups can be quite complex and require that reconnected cables are done consistently.
You can learn more about connecting MIDI devices with the traditional MIDI cable to an iPad or iPhone in our MIDI Setup Tutorial Video.
USB cables became predominate at the turn of the century as a means to transmit digital data. MIDI followed suit and has since allowed MIDI transmissions to occur on top of the USB data link. MIDI calls these various ways to connect peripherals "transports" as the MIDI concepts remain the same even if the cable, or lack there of, is how the data is being sent.
When you have MIDI equipment with a USB port, you may be able to send MIDI over that transport. You may need to check with the manufacturer to make sure that the device supports MIDI over the MIDI port. When it does, you simply connect devices in a similar fashion to other USB peripherals. You can connect multiple devices using a USB hub, limited only to the USB standard being used. Most USB hubs support between 4 and 16 devices. You can add more with more hubs with a maximum number of devices of 127 including each hub. USB cables are limited to 3 meters (10 feet) between powered hubs. While this approach allows you to use many devices, they still can only connect to one host device.
A big plus to using USB as a transport for MIDI is that it can also provide power to the instrument. The downside to this is that iPads and iPhones are mobile devices that don't have a USB cable so you'll need to purchase a USB Camera Connect Kit from Apple. In addition, mobile devices limit the power sent over the USB port which can cause the device to not connect. Check with your manufacturer to see if the device can be used with an iOS device. You can learn more about connecting USB equipment to an iPad in our MIDI Setup Tutorial Video.
At the advent of personal computer networking, the MIDI protocol could travel on another transport – Ethernet. The topology of networks allows for many more devices to be connected. Since each device is a node on the network, it allows for these virtual MIDI ports to be much more flexible. For instance, MIDI sent from one computer could be "heard" from every other computer on the network session. With wireless networks, this becomes even more exciting as complex MIDI arrangements can be designed without the tangle of wires. With proper firewall and router configurations, MIDI could even travel around the world.
The challenge with MIDI over networks is latency. While hard-wired copper wires like Ethernet are low-latency, MIDI over WiFi incurs any latency in the wireless system. While this has gotten better in recent years, there is still an inherent latency that prevents you from performing more time sensitive features like MIDI clock. This also requires a MIDI Network Session to be started and maintained by a host. This is easily possible using Apple macOS and the Audio MIDI Setup tool, but it more challenging on other platforms. It also requires a computer which may be an additional expense and complexity.
You can learn more about setting up a network session in our MIDI Facebook Live Broadcast.
MIDI has recently moved into the realm of low energy Bluetooth promising a future without wires. There are low-cost adapters on the market that you can use to connect instruments with transition MIDI ports or USB ports to become Bluetooth-enabled. Because Apple macOS and iOS operating systems have MIDI built-in with great Bluetooth support, this is even available between Apple devices. One drawback to this transport is that Bluetooth is typically point-to-point, pairing to a single host device. But if you want to simply connect Bluetooth peripherals to an iPad, you can easily connect up to 16 devices without wires. Just keep in mind that because this is wireless, you shouldn't depend on Bluetooth for applications that require extreme low latency like MIDI clock. You can learn more about Bluetooth MIDI in beginning of our BeatBuddy Tutorial Video.
If you are looking to control multiple iPads, computers, MIDI hardware, etc... things get more involved depending on what transports you have available and the equipment you are using. The best way to manage this is through a MIDI hub. iConnectivity sells the iConnectMIDI4+ which can connect up to three computers and four MIDI devices (in/out) as well as has an Ethernet cable to connect to a router for setting up a MIDI network session too! It's a very powerful piece of kit for complex MIDI tasks. It also comes with software that allows you to do some advanced routing of MIDI signals. For instance, if you want the input from MIDI #3 to go to Computer #1, etc.
While you typically need to connect hardware together like instruments, effects processors and computers, more and more these devices are available as software running on increasingly powerful computers like the Apple MacBook Pro. In these cases, no transport is needed, but MIDI can still be used to communicate between software applications. Virtual MIDI allows developers of this software to configure virtual ports that other software running on the same machine can use to send and receive MIDI. You can learn more in our Virtual MIDI Tutorial Video.
Be sure to watch all of our MIDI Tutorial Videos to learn more about the potential of using OnSong to control your entire rig.