Software

Enabling memlock for rtpmidi on Ubuntu 20.10

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In version 0.5.2 of McLaren Labs’ rtpmidi, we made the use of locked memory the default. Locked memory dedicates fixed RAM to the rtpmidi process, and prevents it from being swapped to disk. The use of locked memory (through the mlockall() function call) can be a benefit to realtime applications like MIDI and Audio, but its use can be to the detriment of other processes. So it should be used carefully.

On Ubuntu 18.04 and 20.04 enabling memlock as the default option seemed benign enough. On Ubuntu 20.10, however, this default caused problems. With memlock enabled, the process printed strange errors and aborted. Example:

***MEMORY-ERROR***: rtpmidi[2023]: GSlice: failed to allocate 8176 bytes (alignment: 8192): Cannot allocate memory

Ubuntu 20.10 (Groovy Gorilla) accounts for locked memory pages differently, and even though the memory limit is higher, with all things accounted for, it is not enough.

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Run rtpmidi as a service on Raspberry Pi

A service is a program that the operating system automatically starts when it boots. On the Raspberry Pi “buster” operating system, the daemon that starts and stops services is called “systemd.” You can read about creating services here:

https://www.raspberrypi.org/documentation/linux/usage/systemd.md

McLaren Labs rtpmidi can be run as a service so that whenever you start your Raspberry Pi rtpmidi can be ready to go. This is especially useful in a headless system where you want rtpmidi to route incoming RTP MIDI sessions to a specific MIDI destination.

One of our customers wanted to know how to do this, so we wrote up this HOWTO guide. Here we will show how to create a service that

  • listens for incoming RTP-MIDI connections
  • connects to MIDI Alsa port 128
  • announces itslef on UDP Port 5006
  • logs its output to Syslog
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McLaren Labs rtpmidi Version 0.5.0

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This month McLaren Labs releases rtpmidi version 0.5.0 for Ubuntu and Raspberry Pi. This release brings some great new features, and also provides a few performance and installation improvements.

More MIDI message types … including SysEx

McLaren Labs rtpmidi has always supported the following message types with full Journal capability for sending and receiving. (Note: The Journal is part of the error correction mechanism that recovers lost messages that occur when sent over a network.)

  • Note On, Note Off
  • Control Change
  • Program Change
  • Pitchwheel
  • System Reset

With this release, we also add the following to provide a complete set of MIDI message types including System Exclusive.

Read More »McLaren Labs rtpmidi Version 0.5.0

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.

Read More »The State of Network MIDI (2019)

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

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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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