We have developed a prototype for the visualization of errors while practicing the piano. This prototype will help piano beginners who do not yet have a well-developed hearing to get started and to better recognize their own mistakes. In our visualizations, notes can be displayed in classical notation, in block notation, or as a piano roll. Notes in the block notation have the shape of a rectangle with rounded corners and are drawn in place of classical note heads with a length corresponding to their duration. The user can visualize their piano playing live, or save it and analyze the recordings later. Recording and ground truth notes are visualized through different encodings leveraging either juxtaposition or superposition. We designed an algorithm that matches recorded and ground truth notes to allow for color-encoded error values. Based on piano roll, we designed a heat map visualization, where all pitches are divided into time slices and these slices get different colors depending on whether the recording and the ground truth note is in the same time slice. In our evaluation through case study, we came to the conclusion that only the piano roll notation is suitable for visualizing several recordings at once. The block notation is useful for the display of single recording comparison. Furthermore, the classical notation is generally unsuitable at this stage, because several notes in a narrow range quickly become confusing. The Error Analysis Algorithm serves its purpose when the specified tempo is maintained. Otherwise it can happen that notes are assigned incorrectly.