arts is the sound system of KDE 3. The principle of arts is to create/process sound using small modules which do certain tasks. These may be create a waveform , play samples, filter data, add signals, perform effects like delay/flanger/chorus, or output the data to the soundcard. By connecting all those small modules together, you can perform complex tasks like simulating a mixer, generating an instrument or things like playing a wave file with some effects.