Tobias Erichsen's rtpMIDI brings networked MIDI to the PC. MIDI (Musical Instrument Digital Interface) is a longstanding protocol for digitally transmitting musical information such as notes, the velocity with which a key or drum was hit, and much more. You might also recognize the name from those files used for ring tones in cell phones--just one of the myriad of uses for the protocol.
Originally married to a rather slow serial interface, MIDI is actually hardware-agnostic. With the advent of both wired and wireless networking, the advantages of piggybacking that communications standard became apparent. Apple stole a march on Microsoft by including networking MIDI with its Core MIDI API as of Mac OS X 10.4 (Tiger). With Core MIDI you can musically connect Macs with other Macs--and importantly, with devices such as iPhones and iPads running iOS 4.2 or higher.
Core MIDI and rtpMIDI both are largely based on the RFC-4695 standard developed by Jeff Lazzaro, which utilizes the open data streaming standard RTP (Real-time Transport Protocol) used in Voice over IP and lots of other stuff. But Apple used its own session initialization--and networked MIDI is still not part of the Windows operating system.
To the rescue comes Tobias Erichsen with his rtpMIDI service and virtual MIDI driver, which allow you to connect your PC via MIDI with Macs, iPhones, and iPads. That is a very cool thing as there are numerous IOs apps that let you control recording software and play instruments (software or hardware) remotely--TouchOSC, Lemur, V-Control, MIDI Designer, and ProRemote, just to name a few. Just one application is using the iPad in a vocal booth to control your recording software remotely. It's not as good as having an audio engineer, but cheaper.
Installing rtpMIDI is easy, but you must have Apple's Bonjour installed and enabled or you'll have issues. The well-written installation and configuration instructions can be found on Tobias's site. It took me a reboot before rtpMIDI would work, and you may have to forward the TCP/UDF ports used by the program (5004 and 5005) in your router and/or the Windows firewall before it will function correctly. Once installed, you must run the rtpMIDI client to establish a connection between your PC and your IOs device. The client is a clone of the Audio MIDI window on the Mac.
To get the best performance out of rtpMIDI you need a wireless dongle for your PC configured to create an ad hoc network. You can connect via your main router's Wi-Fi, but latency (the lag between and action and the musical result) will be anywhere from 20 to 100ms--far too slow for real time use. On an ad hoc network the latency will drop significantly to less than 5ms in some instances, which is almost imperceptible. Note that you might still have 20-25ms of additional lag if you're not using ASIO drivers, as this is natural for the normal Windows WDM drivers.
RtpMIDI is a game changer for PC MIDI users, so throw Tobias a couple of bucks via PayPal if you find it useful. iPad developers should contribute also, as being able to control PCs in addition to Macs is bound to increase their sales.
Note: The Download Now button takes you to the developer's website, where you can download the latest version of the software.