Rhythm is movement, and it needs to be studied as movement, not as notation.

Micro-rhythms produce "swing", "groove", "rock", and feelings in music. They activate the tapping of toes and the drive to get up and dance. Academic studies of recordings of live and "live in the studio" recordings (real time, no overdubs or splices, no click tracks, etc.) reveal that all genres have fractal variations in timing down to microseconds. This is analogous to bio-rhythms and neural frequencies like ECG and EEG which are also fractal.

I believe that rhythm encodes heartbeats, neural patterns of motor control, and thought patterns through fingers and lips. Musicians often synchronize breathing (esp. winds) and heartbeat, and in moments of group euphoria the audience is aligned as well. The production of melodic variations (composition, spontaneous or fixed) has been linked to the ability to dance across species.

So-called "New Complexity" music has detailed and precise notation of rhythms that is often scoffed at, but is in the realm of rhythmic expression and includes odd order polyrhythms, quintuplets, and rests with values in different divisions than notes, and different time signatures in left and right hands for examples. Humans can cognize timing to at least 3 microseconds, and master drummers play with the precision to speak to that neural capability.

There is also development of micro-tonal notation and performance to a precision of 1 cent, and even phase locked high ratio just intonation. This is related because rhythm is a lower pitch that interacts with the harmonic structure of tonal pitches and overtone structures (cf. William Sethares).

All of this is obscured in recorded music. Loudspeakers have universal flaws that distort rhythm - they are all measured, specified and designed for frequency response, but distort time and transients. Every knob and digital function in a studio that changes the character of the sound inherently distorts time as well, as does spot miking, mixing, panning, splicing, overdubbing, added delay and reverb.