Pop, Pop!

Pop & Rock Music Structure Analysis from Audio signals

by Yu Shiu

Electrical Engineering Department

University of Southern California

The origin of the project title:

The album of Rickie Lee Jones. In fact, she played all the classical jazz songs in this album. Two "pops" together sounds weird and interesting. It seems that there's something coming out from nowhere. Please notice the bottom-left corner, which is a trademark for an unknown Chinese medicine company. In addition, the description on the album reads like that on the box for medicine. Rickie Lee Jones is one of my favorite singers in college.

Overview of this project:

In this project, I intend to explore the musical structure of pop songs from audio data. Pop and rock music usually have rather simpler musical structure than classical music. The simplicity makes them easy to be familiar with and “catchy”. Basic components of music structure in pop music include intro, bridge, outro and many repetitions of verse and chorus. In my project, given a pop song, I first evaluate the duration and phase of every measure. With assumption of 4/4 time signature, I extract PCP features to represent the chord contents of each sixteenth note. Then, similarity of all the features within this song is presented in a similarity matrix, which clearly reveals the music structure. Chorus is the most easily recognizable pattern in the similarity matrix while verse also shows the similarity among different parts in a song. Many examples of pop and rock songs will be presented and so do the discussions.

Basics for pop & rock music structure

In most cases, there are choruses and verses in pop and rock music. Chorus is the "everybody, sing along" part while verse is the "tell story" part. Chorus tends to repeat for several times and for each time, the lyrics and melody are exactly the same or just change a little bit. Verse tends to change every time. It tells a story or say something relative meaningful. For each time, it changes the lyrics and expands the story while keeps the same melody. In pop and rock music, there are some other parts: intro (the beginning part), bridge (transition from chorus to another verse, sometimes is an instrument solo), outro (the ending part).

Characteristics of pop and rock songs

  1. Relative strong beat: It's easier to estimate the beat of pop and rock songs than that of classics music.

  2. 4/4 time signature: in most cases, pop and rock songs use 4/4 time signature.

  3. Several combination of verse and chorus: For example, VCVCBC or VVCV

Goal of this project

  1. lPresent the pop & rock song in a similarity matrix: repetition parts can be easily seen from the similarity matrix
  2. lUse musical tempo to segment the music properly: music tempo gives the similarity matrix a new time unit so that we could detect the whole repeating patterns precisely.

System overview

  1. I use method which is similar to Scherier's. However, there is confusion between the real tempo and its double or half tempo.
  2. PCP is used to represent the content.
  3. To construct the similarity matrix, the similarity between two one-measure of music signals is   computed by inner product of normalized PCP features (16 PCP for one measure).

Some examples of similarity matrices

1. U2's Vertigo

2. Nirvana's "smell like teen spirits"

 

3. Pixies' "wave of mutilation"

4. Beatles' "hey jude"

Discussion

1. The "deep blue" part along  the off-diagonal lines of similarity matrix represents repeating parts.

2. The chorus is easier to detect from the similarity matrix than the verse.

3. The dissimilar part between very similar parts is usually instrument playing without vocal sounds.

4. In Beatles' "hey, jude", the second half over 2 minutes is composed of one sentence only. It repeats many, many times. Salute to you, beatles.

 







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