There’s a fair amount of info in earlier posts about Sonify itself, but here’s a bit more info on the processes specific to Global Drifter.
The buoy data is transformed into the sounds that you hear at the beginning of the piece and that run throughout. They’re essentially just left to run through the whole piece, although a couple of times I lowpass them for a short time while I introduce new parts of the piece (the lowpass frequency drops abruptly and then does a slow rise back up). You’re hearing six buoys which start very near each other (about midway between Cuba and West Africa) and then diverge over a two-year period (all of 2011 and 2012). What this means is that the six buoys start out with a pretty similar timbre, and then get less similar over the course of the piece.
You can hear just the buoy sounds by themselves here.
Each buoy is being voiced by an identical instance of the Zebra soft synthesizer, each one with its own distinct pitch which is constant throughout the piece. Each buoy is reporting three measurements (latitude, longitude, and temperature), each of which is being mapped to a parameter of the corresponding Zebra instance. Latitude is mapped to oscillator waveform, which is shifting between a square wave and a spike. Longitude is mapped to the intensity of a combined bandpass and bandreject filter being applied to the oscillator. The oscillator runs into an FM oscillator, and temperature is mapped to the rate of an LFO controlling FM depth.
Those are purely aesthetic choices. There are a handful of mapping possibilities that make some kind of objective sense — for example, I could have mapped longitude to stereo positioning — but generally it’s fairly arbitrary. I did want it to be possible, with a little practice, to know roughly what the data are doing based on the sound. Temperature is the easiest — LFO rate stands out, especially when it gets fast, and so you know that the buoys which have that fast LFO sound at any given time are the ones that have drifted into warmer waters.
Once I had the buoy part done, the rest was just about putting it in context (in this case, an electronic dance music context). Mostly I added percussion and bass. My intention was to keep the setting fairly simple so that the sonified data could be the primary element. Probably the sound that competes with it the most is the skittery high-pitched percussion that comes in around 2:30, which is the modified sound of me whacking on some bamboo, recorded with a Zoom stereo field recorder. The first sound that comes in other than the buoys (around 0:30) is an instrument I built from a sample of noise from (if I remember right) a very early phonograph recording; it felt really right to me in this piece because somehow it reminds me of sonar.
Again, see earlier posts for more info on the Sonify API that I created to do this (or see the Sonify page itself). If anyone who’s read this far is interested in working with the API, feel free to reach out for support; I’m very interested in having other folks use it.