Tempo variations in recordings

Hey all,

Ran across an interesting article today on tempo variation in recordings, which can be found here: http://musicmachinery.com/2009/03/02/in-search-of-the-click-track/. The author sought to find out which bands tend to use click tracks (metronome clicks fed through headphones into the drummer’s ears) to maintain a steady tempo throughout a recording and which prefer not to. He created a computer script that first computed the average beats per minute throughout the song and then tracked the deviations from that average over time. It’s pretty clear which groups use click tracks and which don’t. I think this does a great job of highlighting just how much natural variation in tempo performers create on their own, and also brings up a bit of confusion for me. Assuming that the non-click-track groups intended to keep a steady beat, why is it that we have such difficulty maintaining a steady beat on our own? If entrainment is a reflection of internal neural oscillations, why is it that we have so much trouble maintaining regularity in the frequency of these oscillations? (Perhaps London discusses this, and I missed it?)

(Side note: the author also includes a link to an app he created where you can input your own favorite songs and see if they use a click track. Pretty neat!)