With the advent of computer technologies, composers have begun to use computers for their compositions. Among many new compositional techniques, sound analysis and synthesis is a fundamental process for creating new timbres. Accordingly, computer technologies have changed composers' actions during their compositions as well. Because they may forgo writing sketches and scores on paper, some studies point out that it is difficult to analyze the compositional process of music created with computers. To address this issue, we present a visual analytics system, Spectrail, to trace a compositional process made with sound analysis and synthesis using data taken from a software system, AudioSculpt. In this paper, after providing an overview of the latest version of Spectrail, the results of an empirical evaluation experiment with four composers who studied at IRCAM are presented. The actual analytics was performed with two aspects-one is how the composer used computers, and the other is how he changed the sounds during the composition. The results of the evaluation experiment show that the features in the compositional processes are clarified through visual analytics and that the system allows composers to look back on their compositional processes for future creation.