Thursday, April 9, 2009

Rubato, ma non troppo

Today a cool toy called the Echo Nest BPM Explorer was released. As discussed here and here, this makes it easy to analyze a piece of music to determine whether the performer used a click track or metronome.

Since my last post on music in 5/4 included one track with and one without a metronome, let's give it a test.

Here is a BPM chart for my rendition of the Bartók piece.
There is some variation around the beat, but not much, because I was sticking close to the metronome. (Something I rarely use.) The scale bars show that this variation is confined to a narrow range. The green line is a smoothed-out version of the instantaneous BPM, shown in white.

Here is the BPM chart for my rendition of the "Serenade".

There is much more variation going on there. Some of that is intentional rubato, though partially subconscious. But there is also a gradual increase in tempo from beginning to end. That is not intentional, but is probably common when I make recordings. Near the end I start thinking "Hey, this take seems ok! I'd better hurry and finish it before I goof up."

Finally, a more interesting example from Candlefire.

There is the same gradual speed-up as before. I often have that problem with Nyman, because his tempos are absolutely glacial in some cases. But the more interesting thing is the way the white line wiggles up and down regularly. As I explained before, this piece shifts back and forth between 3/4 and 4/4 in an interesting way which gives the impression of speeding-up and slowing-down. It appears that Echo Nest is fooled, just like a human listener would be. Though I'll need to study this more closely to figure out where it really thinks the beats are.

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