Open Sound Control
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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. Bringing the benefits of modern networking technology to the world of electronic musical instruments, OSC's advantages include interoperability, accuracy, flexibility, and enhanced organization and documentation.
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, where higher resolution and a richer musical parameter space is desired. OSC messages are commonly transported across the internet and within home and studio subnets using (UDP/IP, Ethernet). OSC messages between gestural controllers are usually transmitted over serial endpoints of USB by being wrapped in the SLIP protocol.
OSC gives musicians and developers more flexibility in the kinds of data they can send over the wire, enabling new applications that can communicate with each other at a high level.
- Open-ended, dynamic, URL-style symbolic naming scheme
- Symbolic and high-resolution numeric argument data
- Pattern matching language to specify multiple recipients of a single message
- High resolution time tags
- "Bundles" of messages whose effects must occur simultaneously
There are dozens of implementations of OSC, including real-time sound and media processing environments, web interactivity tools, software synthesizers, a large variety of programming languages, and hardware devices. OSC has achieved wide use in fields including new computer-based interfaces for musical expression, robotics, video performance interfaces, wide-area and local-area networked distributed music systems, inter-process communication, and even from within a single application.
The TUIO community standard for tangible interfaces such as multitouch is built on top of OSC. Similarly the GDIF system for representing gestures integrates OSC.
OSC is used extensively in experimental musical controllers and has been built into several open source and commercial products, (See Implementations.)
The Open Sound World (OSW) music programming language is designed around OSC messaging.
OSC is also used as 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 synths.
OSC messages consist of an Address pattern, a Type tag string, Arguments and an optional time tag. Address patterns form a hierarchical name space, reminiscent of a Unix filesystem path, or a URL. Type tag strings are a compact string representation of the argument types. Arguments are represented in binary form with 4-byte alignment. The core types supported are
- 32-bit two's complement signed integers
- 32-bit IEEE floating point numbers
- Null-terminated arrays of 8 bit encoded data (C-style strings)
- arbitrary sized blob (e.g. audio data, or a video frame)
Applications commonly employ extensions to this core set. More recently some of these extensions such as a compact Boolean type were integrated into the required core types of OSC 1.1.
The advantages of OSC over MIDI are primarily internet connectivity; data type resolution; and the comparative ease of specifying a symbolic path, as opposed to specifying all connections as 7-bit numbers with 7-bit or 14-bit data types.
Examples of software with OSC implementations:
- Crystal Space
- Digital Performer
- Isadora (v.1.1)
- Overtone (Clojure)
- Pure Data
- Quartz Composer (as of v3.0 / Mac OS X v10.5)
- Traktor DJ Studio
Examples of hardware with OSC implementations:
- Schmeder, A., Freed, A., and Wessel, D., "Best practices for Open Sound Control", Linux Audio Conference, Utrecht, The Netherlands, 2010.
- Freed, A., Schmeder, A., "Features and Future of Open Sound Control version 1.1 for NIME", NIME Conference 2009.
- Wright, M., Freed, A., "Open Sound Control: A New Protocol for Communicating with Sound Synthesizers", International Computer Music Conference, Thessaloniki, Greece, 1997.