I remember once seeing a "dictionary" of songs. Each one was indexed by whether notes were higher, lower or the same as the previous note. Using D for down, S for same and U for up, and using # for the first note, here's the Start Spangled Banner ...

    #DDUUUUDDDUUSSUDDDDUUSDDD

Many, many tunes can be separated with the first 20 symbols.

Anyone have a reference? I'd like to acquire a copy ...