Felix is our recent PC-based TTS research-system for testing, analyzing, and evaluating TTS algorithms. The object-oriented interface allows efficient algorithm improvement and overall system prototyping by combining different modules. The re- sults of each TTS-processing step can be monitored and all kinds of data may be reviewed and modified. The paper will outline the algorithms currently implemented in the Felix system, focusing on lexical analysis, duration modeling, and source signal generation, where we suggest ways to improve intelligibility and naturalness of synthetic speech.