Codebooks

The set of model vectors of a SOM is referred to as its codebook. Visualizing these codebooks provides useful information for interpreting the SOM since each model vector exhibits features of the assigned data items.

In the figures below, visualizations of the codebooks are shown. The upper two images depict visualizations for the rhythm-based similarity measure RP/MFS, whereas the ones below visualize timbre-based features of the SH-measure. Basically, there are two different methods for scaling. The values can be scaled locally (figures on the left) or globally (figures on the right). Local scaling means that the values of each model vector are mapped to the complete color range available. Hence, the minimum and maximum of each of the model vectors are projected to the lower end and upper end of the color scale, respectively. In contrast, global scaling means that equal values in different model vectors are visualized using the same color. Thus, the minimum and maximum of all values in all model vectors are considered when creating the projection to the color scale.

If the user intends to get an idea of the overall shape of the model vectors, the locally scaled representation is useful. If he/she wants to emphasize the distinctive features (e.g. strong beats), global scaling should be used instead.