The computer-implemented system stores user performance data representing multiple parts. The system also stores style data representing various different musical accompaniments that are displayed in a style data window. The user selectively copies constituent parts of the style data into a user performance data window, thereby incorporating the copied parts into the performance data. Tone pitches and musical length of the copied parts are automatically modified to suit the chord information and timing represented in the existing performance data. As the user records performance data, the on-screen start switch is displays differently (e.g., different color) to show whether the specific part corresponds to a recording part or a non-recording part.