OSC Support

Overview

Most Faust architectures provide Open Sound Control (OSC) support (the implementation is based internally on the oscpack library by Ross Bencina). This allows applications to be remotely controlled from any OSC-capable application, programming language, or hardware device.

OSC support can be added to any Faust program (as long as the target architecture supports it: see tables below) simply by adding the [osc:on] metadata to the standard option metadata:

declare options "[osc:on]";

The following tables provides a list of Faust architectures providing OSC support.

Linux Faust Architectures with OSC Support

Audio System Environment
Alsa GTK, Qt, Console
Jack GTK, Qt, Console
Netjack GTK, Qt, Console
PortAudio GTK, Qt

OSX Faust Architectures with OSC Support

Audio System Environment
CoreAudio Qt
Jack Qt, Console
Netjack Qt, Console
PortAudio Qt

Windows Faust Architectures with OSC Support

Audio System Environment
Jack Qt, Console
PortAudio Qt

Other Faust Architectures with OSC Support

Environment
Android
iOS
JUCE
Bela

Simple Example

To illustrate how OSC support works let's define a very simple noise generator with a level control (we'll call it noise.dsp):


import("stdfaust.lib");
process = no.noise*hslider("level",0,0,1,0.01);

This example can be compiled as a standalone Jack Qt application with OSC support simply by running the following command:

faust2jaqt -osc noise.dsp

When the generated application is ran from the command line:

./noise 

various information is printed in the standard output, including:

Faust OSC version 0.93 application 'noise' is running on UDP ports 5510, 5511, 5512

Hence, the OSC module makes use of three different UDP ports:

These OSC parameters can be changed from the command line using one of the following options:

For example:

./noise -xmit 1 -desthost 192.168.1.104 -outport 6000

will run noise with transmission mode ON, using 192.168.1.104 on port 6000 as destination.

Automatic Port Allocation

In order to address each application individually, only one application can be listening on a single port at one time. Therefore when the default incoming port 5510 is already opened by some other application, an application will automatically try increasing port numbers until it finds an available port. Let say that we start noise and mixer (two Faust-generated applications with OSC support) on the same machine, we'll get the following:

$ ./noise &
...
Faust OSC version 0.93 application 'noise' is running on UDP ports 5510, 5511, 5512
$ ./mixer
...
Faust OSC version 0.93 application 'mixer' is running on UDP ports 5513, 5511, 5512

The mixer application fails to open the default incoming port 5510 because it is already opened by noise. Therefore it tries to find an available port starting from 5513 and opens it. Please note that the two outcoming ports 5511 and 5512 are shared by all running applications.

Discovering OSC Applications

The commands oscsend and oscdump from the liblo package provide a convenient mean to experiment with OSC control and potentially debug applications with OSC support.

`oscsend [hostname] [port] [address] [types] [values]`: sends OSC messages 
via UDP. `[types]` is a string, the letters indicates the type of the following 
values: `i=integer`, `f=float`, `s=string`, etc.
`oscdump [port]`: receives OSC messages via UDP and dump to standard output

Note that OSC messages can be sent from any OSC-compatible applications (e.g., PureData, Max/MSP, etc.).

In the following examples, we'll use two separate terminal windows. The first one will be used to send OSC messages to the noise application using oscsend. The second terminal will be used to monitor the messages sent by the application using oscdump. Commands executed on terminal 1 will be preceded by T1$. Messages received on terminal 2 will be preceded by T2:. To monitor on terminal T2 the OSC messages received on UDP port 5511, oscdump will be used:

T2$ oscdump 5511

Once set we can use the hello message to scan UDP ports for Faust applications. For example:

T1$ oscsend localhost 5510 "/*" s hello

gives us the root message address, the network and the UDP ports used by the noise application:

T2: /noise siii "192.168.1.102" 5510 5511 5512

Discovering the OSC Interface of an Application

The OSC interface of an application (the set of OSC messages we can use to control it) can be discovered by sending the get message to the root:

T1$ oscsend localhost 5510 /noise s get 

As an answer to this OSC message, a full description is printed in terminal T2:

T2: /noise sF "xmit" #F
T2: /noise ss "desthost" "127.0.0.1"
T2: /noise si "outport" 5511
T2: /noise si "errport" 5512
T2: /noise/level fff 0.000000 0.000000 1.000000

The root of the OSC interface is /noise. Transmission is OFF, xmit is set to false. The destination host for sending messages is 127.0.0.1, the output port is 5511 and the error port is 5512. The application has only one user interface element: /noise/level with current value 0.0, minimal value 0.0 and maximal value 1.0.

Widget's OSC Address

Each widget of an application has a unique OSC address obtained by concatenating the labels of it's surrounding groups with its own label.

There are potential conflicts between widget's labels and the OSC address space. An OSC symbolic name is an ASCII string consisting of a restricted set of printable characters. Therefore to ensure compatibility spaces are replaced by underscores and some other characters (asterisk, comma, forward, question mark, open bracket, close bracket, open curly brace, close curly brace) are replaced by hyphens.

Here is as an example, a very simplified monophonic audio mixer with 4 inputs and one output. For each input we have a dmute button and a level slider:


input(v) = vgroup("input %v", *(1-checkbox("mute")) : *(vslider("level", 0, 0, 1, 0.01)));
process = hgroup("mixer", par(i, 4, input(i)) :> _);

If we query this application:

T1$ oscsend localhost 5510 "/*" s get 

We get a full description of its OSC interface on terminal T2:

T2: /mixer sF "xmit" #F
T2: /mixer ss "desthost" "127.0.0.1"
T2: /mixer si "outport" 5511
T2: /mixer si "errport" 5512
T2: /mixer/input_0/level fff 0.0000 0.0000 1.0000
T2: /mixer/input_0/mute  fff 0.0000 0.0000 1.0000
T2: /mixer/input_1/level fff 0.0000 0.0000 1.0000
T2: /mixer/input_1/mute  fff 0.0000 0.0000 1.0000
T2: /mixer/input_2/level fff 0.0000 0.0000 1.0000
T2: /mixer/input_2/mute  fff 0.0000 0.0000 1.0000
T2: /mixer/input_3/level fff 0.0000 0.0000 1.0000
T2: /mixer/input_3/mute  fff 0.0000 0.0000 1.0000

As we can see, each widget has a unique OSC address obtained by concatenating the top level group label "mixer," with the "input" group label and the widget label (see the Labels as Pathnames Section). Please, note that blank spaces are replaced by underscores and metadata are removed during this operation.

All addresses must have a common root. This is the case in our example because there is a unique horizontal group mixer containing all widgets. If a common root is missing as in the following code:

input(v) = vgroup("input %v", *(1-checkbox("mute")) : *(vslider("level", 0, 0, 1, 0.01)));
process = par(i, 4, input(i)) :> _;

then a default vertical group is automatically create by the Faust compiler using the name of the file mix4 as label:

T2: /mix4 sF "xmit" #F
T2: /mix4 ss "desthost" "127.0.0.1"
T2: /mix4 si "outport" 5511
T2: /mix4 si "errport" 5512
T2: /mix4/input_0/level fff 0.0000 0.0000 1.0000
T2: /mix4/input_0/mute  fff 0.0000 0.0000 1.0000
T2: /mix4/input_1/level fff 0.0000 0.0000 1.0000
T2: /mix4/input_1/mute  fff 0.0000 0.0000 1.0000
T2: /mix4/input_2/level fff 0.0000 0.0000 1.0000
T2: /mix4/input_2/mute  fff 0.0000 0.0000 1.0000
T2: /mix4/input_3/level fff 0.0000 0.0000 1.0000
T2: /mix4/input_3/mute  fff 0.0000 0.0000 1.0000

Controlling the Application Via OSC

Any user interface element of the application can be controlled by sending one of the previously discovered messages/addresses. For example, to set the noise level of the application to 0.2 the following message can be sent:

T1$ oscsend localhost 5510 /noise/level f 0.2

If we now query /noise/level we get, as expected, the value 0.2:

T1$ oscsend localhost 5510 /noise/level s get
T2: /noise/level fff 0.2000 0.0000 1.0000

Turning Transmission ON

The xmit message at the root level is used to control the realtime transmission of OSC messages corresponding to user interface's actions. For example:

T1$ oscsend localhost 5510 /noise si xmit 1

turns transmission in ALL mode. Now if we move the level slider we get a bunch of messages:

T2: /noise/level f 0.024000
T2: /noise/level f 0.032000
T2: /noise/level f 0.105000
T2: /noise/level f 0.250000
T2: /noise/level f 0.258000
T2: /noise/level f 0.185000
T2: /noise/level f 0.145000
T2: /noise/level f 0.121000
T2: /noise/level f 0.105000
T2: /noise/level f 0.008000
T2: /noise/level f 0.000000

This feature can be typically used for automation to record and replay actions on the user interface, or to remote control from one application to another. It can be turned OFF any time using:

T1$ oscsend localhost 5510 /noise si xmit 0

Use the ALIAS (xmit = 2) mode if you need to restrict the access to your program: when the ALIAS mode is used, only aliases of input elements (sliders, buttons...) can be used to control them, and output elements (bargraph) will only emit on their aliases.

Filtering OSC Messages

When the transmission of OSC messages is ON, all the user interface elements are sent through the OSC connection.

T2: /harpe/level f 0.024000
T2: /harpe/hand f 0.1
T2: /harpe/level f 0.024000
T2: /harpe/hand f 0.25
T2: /harpe/level f 0.024000
T2: /harpe/hand f 0.44
T2: /noise/level f 0.145000
T2: /harpe/hand f 0.78
T2: /noise/level f 0.145000
T2: /harpe/hand f 0.99

We can choose to filter unwanted parameters (or group of parameters). For example:

T1$ oscsend localhost 5510 /harpe si xmit 1 xmitfilter /harpe/level

As a result, we will receive:

T2: /harpe/hand f 0.1
T2: /harpe/hand f 0.25
T2: /harpe/hand f 0.44
T2: /harpe/hand f 0.78

To reset the filter, send:

T1$ oscsend localhost 5510 /harpe si xmit 1 xmitfilter

Using OSC Aliases

Aliases are a convenient mechanism to control a Faust application from a preexisting set of OSC messages.

Let's say we want to control our previous noise example with TouchOSC on Android. The first step is to configure the TouchOSC host to 192.168.1.102 (the host running our noise application) and outgoing port to 5510.

Then we can use oscdump 5510 (after quitting the noise application in order to free port 5510) to visualize the OSC messages sent by TouchOSC. Let's use for that the left slider of "simple layout". Here is what we get:

T2: /1/fader1 f 0.000000
T2: /1/fader1 f 0.004975
T2: /1/fader1 f 0.004975
T2: /1/fader1 f 0.008125
T2: /1/fader1 f 0.017473
T2: /1/fader1 f 0.032499
T2: /1/fader1 f 0.051032
T2: ...
T2: /1/fader1 f 0.993289
T2: /1/fader1 f 1.000000

We can associate this OSC message to the noise level slider by inserting the metadata [osc:/1/fader1 0 1] into the slider's label:

Several osc aliases can be inserted into a single label allowing the same widget to be controlled by several OSC messages

import("stdfaust.lib");
process = no.noise*hslider("level[osc:/1/fader1 0 1]",0,0,1,0.01);

Because the range of /1/fader1 is 0 to 1 (like the level slider), we can remove the range mapping information and write simply :

import("stdfaust.lib");
process = no.noise*hslider("level[osc:/1/fader1]",0,0,1,0.01);

TouchOSC can also send accelerometer data by enabling Settings/Options/Accelerometer. Using again oscdump 5510 we can visualize the messages sent by TouchOSC:

T2: ...
T2: /accxyz fff -0.147842 0.019752 9.694721
T2: /accxyz fff -0.157419 0.016161 9.686341
T2: /accxyz fff -0.167594 0.012570 9.683948
T2: ...

As we can see, TouchOSC sends the x, y and z accelerometers in a single message, as a triplet of values ranging approximately from -9.81 to 9.81. In order to select the appropriate accelerometer, we need to concatenate to /accxyz a suffix /0, /1 or /2. For example /accxyz/0 will correspond to x, /accxyz/1 to y, etc. We also need to define a mapping because the ranges are different:

import("stdfaust.lib");
process = no.noise * hslider("level[osc:/accxyz/0 0 9.81]",0,0,1,0.01);
alias description
[osc:/1/rotary1 0 1] top left rotary knob
[osc:/1/rotary2 0 1] middle left rotary knob
[osc:/1/rotary3 0 1] bottom left rotary knob
[osc:/1/push1 0 1] bottom left push button
[osc:/1/push2 0 1] bottom center left push button
[osc:/1/toggle1 0 1] top center left toggle button
[osc:/1/toggle2 0 1] middle center left toggle button
[osc:/1/fader1 0 1] center left vertical fader
[osc:/1/toggle3 0 1] top center right toggle button
[osc:/1/toggle4 0 1] middle center right toggle button
[osc:/1/fader2 0 1] center right vertical toggle button
[osc:/1/rotary4 0 1] top right rotary knob
[osc:/1/rotary5 0 1] middle right rotary knob
[osc:/1/rotary6 0 1] bottom right rotary knob
[osc:/1/push3 0 1] bottom center right push button
[osc:/1/push4 0 1] bottom right push button
[osc:/1/fader3 0 1] bottom horizontal fader
[osc:/accxyz/0 -10 10] accelerometer
[osc:/accxyz/1 -10 10] accelerometer
[osc:/accxyz/2 -10 10] accelerometer
**_Examples of OSC Message Aliases for TouchOSC (Layout Mix2)._**

OSC Cheat Sheet

Default Ports

Port Description
5510 default listening port
5511 default transmission port
5512 default error port
5513 alternative listening ports

Command Line Options

Option Description
-port n set the port number used by the application to receive messages
-outport n set the port number used by the application to transmit messages
-errport n set the port number used by the application to transmit error messages
-desthost h set the destination host for the messages sent by the application
-xmit 0|1|2 turn transmission OFF, ALL or ALIAS (default OFF)
-xmitfilter s filter the Faust paths at emission time

Discovery Messages

Message Description
oscsend host port "/*" s hello discover if any OSC application is listening on port p
oscsend host port "/*" s get query OSC interface of application listening on port p

Control Messages

Message Description
oscsend host port "/*" si xmit 0|1|2 set transmission mode
oscsend host port widget s get get widget's value
oscsend host port widget f v set widget's value

Alias

Alias Description
"...[osc: address lo hi ]..." alias with , mapping
"...[osc:' address]..." alias with min, max clipping