Embedded Wireless MIDI Control over IEEE 802.11 using RTP MIDI

Wednesday, April 1, 2009 - 17:30
TH 331
Alison Hughes, Apple

This talk presents an embedded transmitter system that can send MIDI note commands wirelessly to a Macintosh computer using the RTP MIDI protocol. The RTP MIDI stream is used to control a software synthesizer running locally on the Macintosh. Because wireless communication exposes the stream to data loss, this implementation includes RTP MIDI's Recovery Journal system. To conserve bandwidth, it employs a highly compressed feed forward mechanism instead of packet retransmission to protect the MIDI stream from artifacts in the case of lost packets. The project's development hardware consists of a Macintosh computer with a wireless card, an AirPort Express Base Station, and a USB MIDI controller keyboard. The MIDI controller connects to the AirPort Base Station via a USB cable and the AirPort sends MIDI data to the Macintosh over radio frequency using 802.11 transmitter hardware. This embedded solution demonstrates that an RTP MIDI transmitter can feasibly be integrated into a MIDI controller device, eliminating the need for an external transmitter device altogether. A real world application might take the form of a battery operated MIDI controller surface that has the 802.11 hardware integrated inside the device. The user of this device could move about freely and untethered, playing a computer software instrument from any place within range of the wireless network.


Alison Hughes is an audio software engineer working at Apple in the CPU hardware group since 2006. She interned at Apple from 2004 to 2005 where she completed two projects: a MIDI test tool suite and an embedded low latency wireless audio streaming implementation. She currently maintains Apple's USB audio class driver. Last December, she finished her master's degree at SFSU in computer science.