Music History Monday: The Evolution of Western Pop Music: USA (1960-2010)

We mark the public release, on May 6, 2015 – nine years ago today – of a scientific/statistical study published by The Royal Society Open Science Journal, a study entitled “The Evolution of Western Pop Music: USA (1960-2010).”

Scoff not, my friends: this was, in fact, a high-end study conducted (and written up) by four high-end scientists: Dr. Matthias Mauch, of the School of Electronic Engineering and Computer Science at Queen Mary University of London, whose current professional title is “Research Manager for Recommender Systems and Music Intelligence at Apple Music”; Dr. Robert M. MacCallum, who teaches in the Division of Life Sciences at Imperial College, London; Dr. Mark Levy, a former research assistant at the Centre for Digital Music at the University of London and for the last three years a principal research scientist at Apple, where he researches potential future applications of machine learning to music creation and listening; and finally, Armand M. Leroi, a professor of evolutionary developmental biology at Imperial College in London.

Scary fine creds on display here: up, down, and sideways.

The study’s abstract is as follows.  I figure it’s better to get it directly from the quartet of Mauch, MacCallum, Levy, and Leroi than to offer up a watered down and abbreviated version of the abstract by yours truly.

“In modern societies, cultural change seems ceaseless. The flux of fashion is especially obvious for popular music. While much has been written about the origin and evolution of pop, most claims about its history are anecdotal rather than scientific in nature. To rectify this, we investigate the US Billboard Hot 100 between 1960 and 2010. Using music information retrieval and text-mining tools, we analyze the musical properties of approximately 17,000 recordings that appeared in the charts and demonstrate quantitative trends in their harmonic and timbral properties. We then use these properties to produce an audio-based classification of musical styles and study the evolution of musical diversity and disparity, testing, and rejecting, several classical theories of cultural change. Finally, we investigate whether pop musical evolution has been gradual or punctuated. We show that, although pop music has evolved continuously, it did so with particular rapidity during three stylistic ‘revolutions’ around 1964, 1983 and 1991. We conclude by discussing how our study points the way to a quantitative science of cultural change.”

Fascinating, yes?

Methodology

The actual paper – “The Evolution of Western Pop Music: USA (1960-2010)” – is rather lengthy; 4614 words (FYI: I let my computer do the word count).  Overall, the paper is characterized by the sort of technical jargon we would expect to find in a scientific journal.  For example: in the course of their introduction, the authors lay out their methodology as follows. 

“We adopted an approach inspired by recent advances in text-mining. We began by measuring our songs for a series of quantitative audio features, 12 descriptors of tonal content and 14 of timbre. These were then discretized into ‘words’ resulting in a harmonic lexicon (H-lexicon) of chord changes, and a timbral lexicon (T-lexicon) of timbre clusters. To relate the T-lexicon to semantic labels in plain English [“plain English”; if only!], we carried out expert annotations. The musical words from both lexica were then combined into 8+8=16 ‘topics’ using latent Dirichlet allocation (LDA). LDA is a hierarchical generative model of a text-like corpus, in which every document (here: song) is represented as a distribution over a number of topics, and every topic is represented as a distribution over all possible words (here: chord changes from the H-lexicon, and timbre clusters from the T-lexicon). We obtain the most likely model by means of probabilistic inference. Each song, then, is represented as a distribution over eight harmonic topics (H-topics) that capture classes of chord changes (e.g. ‘dominant-seventh chord changes’) and eight timbral topics (T-topics) that capture particular timbres (e.g. ‘drums, aggressive, percussive’, ‘female voice, melodic, vocal’, derived from the expert annotations), with topic proportions q. These topic frequencies were the basis of our analyses.”

Got that?

Okay: I am so, so sorry I made you read that; really, I am.  But it was necessary to show you why we aren’t going to get into the details of the study but rather, fairly quickly cut to the study’s conclusions which are, to my mind, of no small interest, methodology aside!…

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