SciTech

How Things Work: Pandora radio

Pandora Radio can be run in a web browser as shown, or as a standalone application. By categorizing music based on certain criteria, called “genes,” Pandora will intelligently select music to play based on a listener’s preferences. (credit: Celia Ludwinski/Assistant Photo Editor) Pandora Radio can be run in a web browser as shown, or as a standalone application. By categorizing music based on certain criteria, called “genes,” Pandora will intelligently select music to play based on a listener’s preferences. (credit: Celia Ludwinski/Assistant Photo Editor)

Since its introduction in 2005, Pandora Radio has steadily developed a strong following. Internet radio has been around since before Pandora, and many stations began to offer music recommendation services, gently directing the listener to other songs they might find interesting based on the tastes of other listeners. Pandora Radio differs from other Internet radio stations in that song recommendations are unique to each user. Pandora allows its users to choose paths of music they find personally tasteful. Notably, none of these recommendations are based on the preferences of other users.

The Music Genome Project was started in January 2000 with the aim of studying all music at a fundamental level. The project aimed to categorize all music based on certain basic musical traits. Five years of research led to a means to do just what they set out to achieve. To date, the Music Genome Project has identified nearly 400 musical traits. Some of these are commonly understood — acoustic rhythm guitars, repetitive chorus — while most others are more complex. These are referred to as “genes.” The project breaks down each song into its component genes. The genes may vary from song to song, with rock music having fewer genes than a classical piece. Each of the selected genes is then assigned a value between one and five in increments of one-half, with higher values indicating a stronger presence of that particular musical trait.

The bank of songs that Pandora uses to select and make recommendations is called the library. This library, according to the Pandora team, consists mainly of English songs and has well over half a million songs, with more being added every day. Approximately 15,000 songs are added to the library every month. Before it is added to the library, a song is studied by a trained analyst who lists the various genes associated with the song. The entire genetic structure of a song is identified in about 20 minutes. Knowing the genes of a particular song, a computer creates a simulated spatial representation. This is done by a classifier program. The function of this program is to identify the song by its spatial genetic representation. When a listener inputs a personal favorite, the system studies the characteristics of the song and creates a vector based on its genes. This vector then points to the next song having similar genes arranged in space in a similar manner. In addition to this method of recommending songs to the listener, Pandora allows the listener to provide feedback to the program, indicating an interest or dislike for a particular song. Allowing the program to recommend songs without providing any feedback to it can result in highly varied song recommendations. A rock song could theoretically point to a classical music piece. The recommendations allow the user to remain within the general area of their personal musical interests.

Submitting a “Thumbs Up” vote causes the program to select and play songs that more closely resemble the song currently playing, while a “Thumbs Down” vote bans the song from the station temporarily and also avoids similar music when making new recommendations. Another constraint on the songs played stems from the music license issues. Pandora is not allowed to play songs “on demand,” replay songs, or play more than four songs by the same artist in an hour. Songs cannot be skipped more than six times an hour or more than 20 times in a day, depending on the kind of subscription.
As Pandora depends on a human analyst — at present, at least — the costs incurred are higher than most other Internet radios. To counter this problem, Pandora Radio offers a free as well as paid listening experience. The former allows only 40 hours of music a month interspersed with advertisements.

Pandora Radio’s Internet presence allows it to be highly accessible by today’s generation of mobile phone users. Over time, Pandora has created a number of desktop gadgets and applications for phones to allow listeners to tune in on the go. Tim Westergren, the founder of Pandora Radio, told the Chicago Tribune how effective releasing a single Pandora mobile phone application was. Within the first 10 days of releasing the application in July 2008, Pandora listeners doubled to 40,000 a day.