Musik im Raum - ZKM

3 Software
The system is controlled by the open source software sWONDER, which has been redesigned for
this purpose. 3 The software can be controlled via OpenSoundControl (OSC) 4 , and there have been
several tools created to use the system, ranging from LADSPA 5 and VST 6 plugins to a 3D graphical
interface.
3.1 Control unit
sWONDER is a “distributed application” that communicates over OSC as shown in figure 5. cwonder
is the glue part that each of the other parts communicates with. The only thing the other parts
need to know is the address of cwonder which can be retrieved from a configuration file. The other
parts, or other applications, can connect to different streams that cwonder sends out:
–
–
–
–
/WONDER/stream/render contains all information to render the audio for the sources.
/WONDER/stream/score contains all information to record and play the source movements.
/WONDER/stream/visual contains all information to display the status of all the sources and
settings.
/WONDER/stream/timer gives a regular update on the current time of the system.
When connected to a stream, cwonder sends out regular messages (“ping”) to which needs to be
replied (with “pong”). If a program that is connected does not reply for a certain amount of time,
cwonder will stop sending data to that program.
Marije Baalman „How to Control 840 Channels“
fig. 5: Schematic overview of the different parts of the sWONDER software. The control unit can communicate with an
arbitrary number of realtime renderers, offline renderers and user interfaces.
3.2 Audio rendering
The real-time render unit is responsible for the actual audio signal processing. It has several ways to
deal with the audio streams: playback of direct sound, utilising weighted delay lines, convolution of the
input sound for early reflections, and convolution of the input sound for reverb followed by a weighted
delay lines to create plane waves with the reverb tail. Schematically this is shown in figure 6.
The rendering engine consists of two parts: twonder for the delay line implementation, and
fwonder for the convolution. Both programs are controlled by OSC; audio input and output has the
audioserver JACK (1http://jackaudio.org) as the audio backend. twonder can deal with the different
type sources: a point source (both behind and in front of the loudspeakers) and plane waves (see
fig. 7).
54