The authors put together a flowchart for automatic classification. I was curious about “detect features of symphony”, especially when one only has a 30 second clip: “Since a symphony is composed of multiple movements and repetitions, there is an alternation between relatively high volume audio signal (e.g. performance of the whole orchestra) and low volume audio signal (e.g. performance of single instrument or a few instruments of the orchestra) along the music piece. … Thus, by checking the existence of alternation between high volume and low volume intervals (with each interval longer than a certain threshold) and/or repetition(s) in the whole music piece, symphonies will be distinguished [from other genres].”
Props to the authors for attempting the impossible, but any flowchart for assigning music genre must be broken from the very first decision. Genres are not uniquely specified by characteristics that mutually exclude others.