thumb | right | iPad running [[TouchOSC]]
Open Sound Control (OSC) is a protocol for networking sound synthesizers, computers, and other multimedia devices for purposes such as musical performance or show control. OSC's advantages include interoperability, accuracy, flexibility and enhanced organization and documentation. Its disadvantages include higher bandwidth requirements, increased load on embedded processors, and lack of standardized messages/interoperability. The first specification was released in March 2002.
Motivation
OSC is a content format developed at CNMAT by Adrian Freed and Matt Wright comparable to XML, WDDX, or JSON. It was originally intended for sharing music performance data (gestures, parameters and note sequences) between musical instruments (especially electronic musical instruments such as synthesizers), computers, and other multimedia devices. OSC is sometimes used as an alternative to the 1983 MIDI standard, when higher resolution and a richer parameter space is desired. OSC messages are transported across the internet and within local subnets using UDP/IP and Ethernet. OSC messages between gestural controllers are usually transmitted over serial endpoints of USB wrapped in the SLIP protocol.
Features
OSC's main features, compared to MIDI, include:
OSC is the heart of the DSSI plugin API, an evolution of the LADSPA API, in order to make the eventual GUI interact with the core of the plugin via messaging the plugin host. LADSPA and DSSI are APIs dedicated to audio effects and synthesizers.
In 2007, a standardized namespace within OSC called SYN, for communication between controllers, synthesizers and hosts, was proposed.
Design
OSC messages consist of an address pattern (such as <code>/oscillator/4/frequency</code>), a type tag string (such as <code>,fi</code> for a float32 argument followed by an int32 argument), and the arguments themselves (which may include a time tag).
Messages may be combined into bundles, which themselves may be combined into bundles, etc. Each bundle contains a timestamp, which determines whether the server should respond immediately or at some point in the future. This human-readability has the disadvantage of being inefficient to transmit and more difficult to parse by embedded firmware, however.