The State of Network MIDI (2019)

Network MIDI was invented sometime around 2004 to send MIDI messages over an IP network. To handle network loss, a protocol known as RTP-MIDI was created and documented as RFC-4695. Network MIDI is built into OSX computers and iOS devices. Apple music creators think nothing of connecting MIDI equipment using Ethernet and WiFi, instead of MIDI cables.

Sometime around 2009, Network MIDI was built into iPads and iPhones. This made building touch-based control surface Apps easy, and ensured they integrated with MIDI Workstations over WiFi. While this capability created many cool demos, the unpredictable latency and jitter of WiFi made MIDI-over-WiFi not attractive where timing is important. MIDI-over-Bluetooth became a standard in the last few years, and seems to be the preferred method for sending MIDI over wireless links.

But Network MIDI persists, and new implementations of the protocol as software pop up, as do new hardware products implementing the protocol. This article is a round-up of some of the implementations available in 2019.

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Why McLaren Labs uses Objective-C

McLaren Labs was started with the idea that music and media creation on Linux should be as easy and fluid as Mac OSX. We had been inspired by AVFoundation and the modular way its pieces fit together. We loved being able to build media pipelines with sources and sinks that cleaned up after themselves when you were done with them them.

Many of the facets of the OSX components we liked were provided by ObjC features enabled by the Clang compiler and LLVM tool suite. LLVM has revolutionized language development by paving the way for Swift and Rust. Back at the time we were getting started, Swift on Linux was gaining traction and we considered adopting it. However, after some initial explorations with Swift and libdispatch, we discovered that libdispatch just wasn’t ready with Swift on Linux. That was in 2015 – Swift on Linux is much more mature. The equation might be different today … but it might not too.

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Yamaha MD-BT01 Bluetooth MIDI adapter to Raspberry Pi

The Yamaha MD-BT01 is a nifty little MIDI 5-pin DIN to Bluetooth adapter.  It plugs into the MIDI In/Out ports of MIDI controllers to connect wirelessly to a computer with Bluetooth.  A typical use for this adapter is to connect legacy MIDI keyboards to a computer without using a 5-pin MIDI to USB adapter on the computer.  Since most computers have Bluetooth built in these days, this makes for a tidy work-area since it eliminates at least one of the cables in your MIDI studio.


The MD-BT01 has a very smart appearance – it consists of just two large plugs connected by a single wire.  It runs off of the current already provided by the 5-pin MIDI signal.  Just plug it in, and it advertises itself as a Bluetooth MIDI connection point.    Since it uses the Bluetooth MIDI standard, it can connect to many different devices.  We tested it with Raspberry Pi and it works fine with Raspbian Stretch.  If you have followed the steps in our previous article (https://mclarenlabs.com/blog/2019/01/15/korg-microkey-air-37-bluetooth-midi-keyboard-with-raspberry-pi/) then your Pi is ready to go.
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Korg Microkey Air 37 Bluetooth MIDI Keyboard with Raspberry Pi

Do you want to have even more fun with your musical Raspberry Pi? Use an external Bluetooth MIDI keyboard with it! For this project, you need to download and compile a new version of the Bluetooth drivers for Linux. If you don’t already have compilation tools installed, you’ll need those too.

We will tell you how to compile and install the necessary Bluetooth driver, and then describe how to pair a Bluetooth MIDI Keyboard.

Prerequisites

You should have a Raspberry Pi 3 with built-in Bluetooth adaptor.
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Punching it Up: Low-latency notes

Sometimes you want a really “punchy” sound. To a musician, this means a sound with a rapid attack and a quick reaction from the keyboard. To a software developer, this means a sound with a very low attack rate and a very low latency through the synthesizer from the keyboard to the audio output. To make a punchy sound, we’re going to use an external USB audio card, and also adjust the sound card settings.

What is Latency?

Latency is the delay from when you hit a note on the keyboard until you hear the sound. Musicians deal with latency all the time, because there are audio delays inherent in all of our equipment. Pipe Organ players have long been accustomed to experiencing a delay between the keyboard action and the sounding of a pipe. However,  organists learn to adapt.
If the value of the latency between the keypress and the sound is constant, a musician has a good chance of being able to compensate. If the latency is unpredictable, even a tiny bit, then a musician will have a harder time keeping their music sounding rhythmic. We are going to try to adjust our organ to reduce latency, and also the variance of the latency.

Why not the internal sound device?

The internal sound chip of the Raspberry Pi 3 is good enough for desktop sounds and casual listening to music, but if you want clearer sounds, and lower latency you will want an external USB sound card. The actual experience you have will vary with the sound card you choose. Here at McLaren Labs we use a Yamaha MG-10XU mixer with USB input as an external sound device and it works great.
Read about how we reduced latency and created a “punchy” sound below the break.
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