Basically, they start with the durations between each note, normalize for differences in tempo, and then create a string that for each note indicates whether the duration goes up, down, or stays the same between each note. Then find the edit distance between that string, and the strings in the database for each song.
You might have to read that a dozen or so times to make any sense of it, but it beats reading the paper if you have work to get done.
Basically, they start with the durations between each note, normalize for differences in tempo, and then create a string that for each note indicates whether the duration goes up, down, or stays the same between each note. Then find the edit distance between that string, and the strings in the database for each song.
You might have to read that a dozen or so times to make any sense of it, but it beats reading the paper if you have work to get done.
If you want to look into it further, http://cgi.sfu.ca/~gpeters/tapper/tapper.cgi .