This is a user-friendly web app for calculating the P-DFT: a DFT in pitch/midi space (see below). To use the app, enter either pitch names (e.g. "C4, G7, E5") and/or midi numbers separated by commas and then hit "calculate." Components represent equal divisions of midi space—a higher magnitude for a component means the signal is well divided into n-parts (where n is the component number).
For more details on the P-DFT, see this presentation by Kahrs and Chiu—publication in Future Directions of Music Cognition. The magnitudes in the graph above are normalized by the cardinality f0. For examining DFT components separated in a vector space, see Jenn Harding's implementation here.