From LQWiki
aRts (analog Real time synthesizer) is an application that simulates a synthesizer under KDE. A component of aRts is the soundserver (aRtsd) which mixes several soundstreams in realtime. aRts is free software, distributed under the terms of the GNU GPL.
The aRts platform also includes aRts builder — an application for building custom sound configurations. Other realtime soundservers are jack and ESD. It is also common to use ALSA's software mixing instead of aRtsd.
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