We propose a system that supports the visualization and visual comparison of MIDI files. As a series of abstract time-related events, MIDI data poses a special set of challenges to the design of visual representations.Based on a set of target user groups and corresponding tasks, we propose a concept and implementation of several visualizations. Multiple MIDI files can be viewed at once in list of cards, each holding a summary of the corresponding file. Our visualization system provides various visualizations for the contents of individual MIDI files. A heatmap is used to provide an overview of the distribution of notes across the channels. We propose a novel approach to the visualization of the occurrence count for each individual note in a hexagonal grid as an alternative to the more traditional implementation of a stacked bar chart. For the visualization of note sequences, we use a pitch-time chart and investigate the capabilities of an adaptation to the MatrixWave visualization for the representation of music. We further explored designs based on arc diagrams as a possibility to visualize similarities between string representations of sequences. To provide support for the visualization of differences between the contents of two MIDI files, we propose comparative views based on the pitch-time chart and the hexagonal grid. We implemented the designs as a browser application, which we evaluated with a usage scenario. The results show that our system supports the specified target users' tasks, but also reveal some limitations of our concept and implementation.