We present SPAWC (Signal Parser And Well-Formed Composer), a system for the generation of complex melodies, chords and sounds, based on a simple interaction of the performer with an input instrument, i.e., a modulator. Via modulator, the performer generates inputs which are manipulated by SPAWC and transformed into melodies, chords or complex sounds. Real/virtual instruments, as well as a set of (pre or live) recorded audio samples can be utilized to produce the final output. In this paper, we describe all the system components working inside SPAWC. The final output is dynamically produced based on the utilized carrier, i.e., the exploited real/virtual instrument or the set of audio samples loaded on SPAWC. A real installation of SPAWC has been developed by exploiting a theremin as the modulator. Real experiences have demonstrated that SPAWC can be utilized by artists to produce interactive music generation experiences. Concurrently, the system can be employed for entertainment and educational purposes. The software architecture of SPAWC is designed to allow the distribution of its software components over a network. This would make possible to dynamically exploit different carriers available on the net, and promote novel forms of artistic interactions among users over the Internet.