OSC and MIDI Networking
Definition
Control protocols carry commands between devices: a playback system triggering the lighting, a tablet driving a console, or a show controller firing cues across several departments. OSC (Open Sound Control), whose 1.0 specification was published in 2002, is a message protocol independent of its transport. It is usually sent over UDP, and it can also run over TCP or over serial links with SLIP framing. Its messages use readable address patterns such as /cue/12/go and carry typed data, and wildcards in the pattern let one message reach several destinations.
The guide
MIDI is an older standard that remains widely used. The original MIDI 1.0 link is a serial connection at 31.25 kilobaud. MIDI also travels over USB and over IP networks, for example as RTP-MIDI (RFC 6295), which removes the limits of the original cabling. MIDI Show Control (MSC), ratified by the MIDI Manufacturers Association in 1991, adds show commands such as GO, STOP and RESUME, and ordinary note and control-change messages are also used for triggering and automation.
A control path carries neither audio nor video, yet it is part of the show. A lost OSC packet or a stalled MIDI link means that a cue does not fire, and the audience perceives the result in the same way as a dead speaker or a black screen. Control links are therefore included in line-checks and in redundancy planning like the media paths.
The rule
A failed control link has the same effect on the show as a failed audio or video link.
Sources
- CNMAT, The Open Sound Control 1.0 Specification (2002) : protocole indépendant du transport, UDP, TCP, motifs d'adresse et caractères génériques · opensoundcontrol.stanford.edu
- Freed et Schmeder, Features and Future of Open Sound Control version 1.1 (NIME 2009) : transport série avec encadrement SLIP · opensoundcontrol.stanford.edu
- MMA, MIDI 1.0 Electrical Specification Update (CA-033) : liaison série à 31,25 kbauds · midi.org
- IETF RFC 6295 (2011) : RTP Payload Format for MIDI (RTP-MIDI) · datatracker.ietf.org
- MIDI Manufacturers Association, MIDI Show Control 1.0 (RP-002, 1991) : commandes GO, STOP, RESUME · richmondsounddesign.com
- MIDI Association, MIDI Show Control : RP-002 publié en 1991 · midi.org