The most recognizable features of the jazz phrasing style known as “swing” is the articulation of tactus beat subdivisions into long-short patterns (known as “swing eighths”). The subdivisions are traditionally assumed to form a 2:1 beat-upbeat ratio (BUR); however, several smaller case studies have suggested that the 2:1 BUR is a gross oversimplification. Here we offer a more conclusive approach to the issue, offering a corpus analysis of 456 jazz solos using the Weimar Jazz Database. Results indicate that most jazz soloists tend to play with only slightly uneven swing eighths (BUR = 1.3:1), while BURs approaching 2:1 and higher are only used occasionally. High BURs are more likely to be used systematically at slow and moderate tempi and in Postbop and Hardbop styles. Overall, the data suggests that a stable 2:1 swing BUR for solos is a conceptual myth, which may be based on various perceptual effects. We suggest that higher BURs are likely saved for specific effect, since higher BURs may maximize entrainment and the sense of groove at the tactus beat level among listeners and performers. Consequently our results contribute with insights relevant to jazz, groove, and microrhythm studies, practical and historical jazz research, and music perception.

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