Ever wondered how inverted music would sound like? Do you know what the original song is of this inverted song (and don’t look at the URL!)? In this post, some MIDI files are inverted and it is shown how you can invert a MIDI file yourself.
As inspired by this video, inverted music is defined as follows here. Suppose there is a basenote of value $V$. Any note of value $X$ will be changed in opposite direction, such that the inverted note has value $V + (X – V)$. So, the function $f$ which inverts a note is defined as $f(X) := V + (X – V)$.
As an example, assume that D is the basenote. A C (which has a distance 2 to D [C C# D]) is converted to an E (a distance 2 in the opposite direction: [D D# E]). Something funny happens with chords. A major chords will become a minor chord once it is inverted. Check it out yourself by looking at $f(X)$, $f(X+4)$ and $f(X+7)$.
The code can be found on GitHub. It just applies the rule above on all the MIDI tracks (except for the drum track).
Inverted MIDI files
It is actually quite fun to experiment with MIDI files. Except for the poor quality of the music, it gives lots of insights into the dynamics of a piece of music. Have fun with inverting your MIDI files :-)!