That’s the title of a paper by E. Glenn Schellenberg and Christian von Scheve, from the May 21, 2012 edition of Psychology of Aesthetics, Creativity, and the Arts. Here is the abstract:

Some musical characteristics are cues to happiness (fast tempo, major mode); others are cues to sadness (slow tempo, minor mode). Listening to music with inconsistent emotional cues leads to mixed feelings and perceptions, or simultaneous happy and sad responding. We examined whether emotional cues in American popular music have changed over time, predicting that music has become progressively more sad-sounding and emotionally ambiguous. Our sample comprised over 1,000 Top 40 recordings from 25 years spanning five decades. Over the years, popular recordings became longer in duration and the proportion of female artists increased. In line with our principal hypotheses, there was also an increase in the use of minor mode and a decrease in average tempo, confirming that popular music became more sad-sounding over time.

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