The Analog Real-time Synthesizer (aRts) provides software that can simulate a complete "modular analog synthesizer" on your computer. It creates sounds and music using small modules like oscillators for creating waveforms, various filters, modules for playing data on your speakers, mixers, and faders. You can build a complete setup with the GUI of the system, using the modules: generators, effects and output -- connected to each other.
aRts provides necessary libraries for KDE, however it can be installed as a standalone package. The installation instructions for aRts can be found in the aRts-1.2.2 portion of the KDE installation instructions.