It has long been known that musicians do not keep time with the precision of a metronome. Here we show that in deviating from a perfectly precise beat, a professional drummer makes patterns in the timing and dynamics that have a particular mathematical form - a fractal [1]. These fractal, long-range correlated deviations make music sound distinctly human [2,3]. On the other hand, the series of cumulative fluctuations from the mean interbeat intervals, i.e., the musical drift or flow, has superdiffusive properties if there is no metronome present [4]. We introduce our audio detection tools and time series analysis methods behind these findings. Our results on musical rhythms are brought to a more general context with other complex physiological signals such as the heartbeat. We also discuss the relevance of our results as a subtle element behind musical "groove" -- among other better known elements such as rhythmic syncopation and musical interplay in the band.

[1] E. Räsänen et al., PLoS ONE 10(6): e0127902 (2015).
[2] H. Hennig et al., PLoS ONE 6(10): e26457 (2011).
[3] H. Hennig et al., Phys. Today. 65, 64 (2012).
[4] E. Räsänen et al., in preparation (2017).