Open Sound Control (OSC)

Open Sound Control (OSC) is an open, transport-independent, message-based protocol for communication between computers, sound synthesizers, lighting software and other multimedia devices. It was created by Matt Wright and Adrian Freed at CNMAT, University of California, Berkeley, and version 1.0 was published in March 2002. DMXDesktop implements OSC in both directions: it receives commands from external controllers and broadcasts state changes to other applications.

Where DMX512 sends a fixed stream of numbered slots, OSC sends named messages. That is the whole difference in one sentence. An OSC message has three parts:

• An address pattern, a text string that starts with a forward slash and reads like a URL path, for example /master/dimmer.
• A type tag string, a comma followed by one letter per argument. Every OSC implementation supports i (32-bit integer), f (32-bit float), s (string) and b (binary blob).
• The arguments themselves, in the order the type tags declare. All numbers are big-endian and every value is padded to a multiple of 32 bits.

Two things surprise people arriving from MIDI or DMX. First, OSC has no official port number. The specification is deliberately transport independent and assigns none, and there is no registered OSC port at IANA either, so each application picks its own and you set it at both ends. DMXDesktop listens on port 8000 by default and sends output to port 9000.

Second, OSC address patterns support wildcards, so one message can reach several destinations at once: ? matches any single character, * matches any sequence of characters, [abc] matches any character in a set, and {foo,bar} matches any string in a list.

OSC also has bundles: several messages grouped together with a 64-bit time tag in NTP format, so a receiver applies them as one atomic group, either immediately or at a scheduled moment. OSC carries the time tag but does not synchronise clocks itself, so both machines need their own correct time.

A note on versions, because it trips people up: OSC 1.1 exists, but there is no 1.1 specification document. Its authors published a paper for NIME 2009 instead and let it stand as the reference. OSC 1.1 keeps the 1.0 message format, promotes several optional types such as True, False, Null and Impulse to required, and adds the // multi-level wildcard. Messages written for 1.0 still work with 1.1 receivers.

1. Open DMXDesktop and navigate to Settings → General
2. In the OSC section, you'll find:
   • Enable/Disable OSC Input toggle
   • Network Interface selection
   • Input Port number (default: 8000)
   • Protocol selection (UDP/TCP)
   • Enable/Disable OSC Output toggle
   • Output Host and Port (default: 127.0.0.1:9000)
3. The discovery service runs on port 9000 and allows compatible apps to automatically find DMXDesktop on the network

• Ensure your device and computer are on the same network
• If using a firewall, allow incoming connections on ports 8000 and 9000
• For optimal performance, use a dedicated network or 5GHz WiFi connection
• For OSC Output, configure the target host IP and port in Settings