In addition to MIDI, another way to get information in and out of Sonic Pi is via the network using a simple protocol called OSC - Open Sound Control. This will let you send messages to and from external programs (both running on your computer and on external computers) which opens up the potential for control way beyond MIDI which has limitations due to its 1980s design.

For example, you could write a program in another programming language which sends and receives OSC (there are OSC libraries for pretty much every common language) and work directly with Sonic Pi. What you can use this for is only limited by your imagination.

By default when Sonic Pi is launched it listens to port 4560 for incoming OSC messages from programs on the same computer. This means that without any configuration, you can send Sonic Pi an OSC message and it will be displayed in the cue log just like incoming MIDI messages. This also means that any incoming OSC message is also automatically added to the Time State which means you can also use get and sync to work with the incoming data - just like with MIDI and synchronising live_loops - see sections 5.7 and 10.2 to recap how this works.

A Basic OSC Listener

Let’s build a basic OSC listener:

In this example we described an OSC path "/osc*/trigger/prophet" which we’re syncing on. This can be any valid OSC path (all letters and numbers are supported and the / is used like in a URL to break up the path to multiple words). The /osc prefix is added by Sonic Pi to all incoming OSC messages, so we need to send an OSC message with the path /trigger/prophet for our sync to stop blocking and the prophet synth to be triggered.

Sending OSC to Sonic Pi

We can send OSC to Sonic Pi from any programming language that has an OSC library. For example, if we’re sending OSC from Python we might do something like this:

Or, if we’re sending OSC from Clojure we might do something like this from the REPL:

Receiving from External Machines

For security reasons, by default Sonic Pi does not let remote machines send it OSC messages. However, you can enable support for remote machines in Preferences->IO->Networked OSC->Allow OSC from other computers. Once you’ve enabled this, you can receive OSC messages from any computer on your network. Typically the sending machine will need to know your IP address (a unique identifier for your computer on your network - kind of like a phone number or an email address). You can discover the IP address of your computer by looking at the IO section of the preferences pane. (If your machine happens to have more than one IP address, hovering the mouse over the listed address will pop up with a list of all known addresses).

Note, some programs such as TouchOSC for iPhone and Android support sending OSC as a standard feature. So, once you’re listening to remote machines and know your IP address you can instantly start sending messages from apps like TouchOSC which enable you to build your own custom touch controls with sliders, buttons, dials etc. This can provide you with an enormous range of input options.

In addition to receiving OSC and working with it using Time State, we can also send out OSC messages in time with our music (just like we can send out MIDI messages in time with our music). We just need to know which IP address and port we’re sending to. Let’s give it a try:

If you run the code above, you’ll notice that Sonic Pi is sending itself an OSC message! This is because we set the IP address to the current machine and the port to the default OSC in port. This is essentially the same as posting a letter to yourself - the OSC packet is created, leaves Sonic Pi, gets to the network stack of the operating system which then routes the packet back to Sonic Pi and then it’s received as a standard OSC message and is visible in the cue logger as the incoming message /osc:127.0.0.1:4560/hello/world. (Notice how Sonic Pi automatically prefixes all incoming OSC messages with /osc and then the hostname and port of the sender.)

Sending OSC to other programs

Of course, sending OSC messages to ourselves may be fun but it’s not that useful. The real benefit starts when we send messages to other programs:

In this case we’re assuming there’s another program on the same machine listening to port 123456. If there is, then it will receive a "/hello/world OSC message with which it can do what it wants.

If our program is running on another machine, we need to know its IP address which we use instead of "localhost":

Now we can send OSC messages to any device reachable to us via our local networks and even the internet!