We’re starting to think that maybe beat tracking, as it’s usually implemented, isn’t really that useful for a lot of jazz. Not only do many jazz tracks seem to confuse beat trackers, but it’s not clear that “beats” are really that useful when asking the kinds of questions we’re interested in.
Here is a 2nd round of graphs looking at tempo over time. But this time I’ve plotted both beat lengths and segment lengths of many versions of Autumn Leaves using the EchoNest analysis engine. Beat detectors try to make an estimate of the track’s tempo and then find a beat grid that maps nicely onto the events in the track. That works well for most pop music, since there is a beat grid to be found. That’s often not quite the case in jazz. Segments are simply short snippets of sound that are meant to represent individual audio events, regardless of tempo/beat. Generally a beat will be composed of several segments, and segments can and often do cross over beat divisions.
The graphs aren’t particularly revelatory, but some of the differences between the beat curves and the segment curves are interesting. Next we need to listen through these while watching the segments curves to see if anything intriguing pops out…
N.B.: The Y axis is now fixed at 0.0-1.0 seconds to make it easier to compare across tracks. This also tames some of the wild jumps in beat length that appeared in the previous graphs.
