Music from the Ocean

by Bob L. Sturm
Composerscientistrecordings, 2002
Audio and Data CD-ROM, 34 tracks, $10.00
Include essay and Flash presentation
Distributor’s website: http://www.composerscientist.com/csr.html.

Reviewed by Stefaan Van Ryssen
Hogeschool Gent
Jan Delvinlaan 115, 9000 Gent, Belgium

stefaan.vanryssen@pandora.be

Nomen est omen: Bob Sturm (Sturm is German for 'storm') makes storms, tides and waves audible on this very interesting and carefully documented CD.

Ocean ripples, waves, and tides have very low frequencies, typically in the range of 0.6 to 0.00002 Hz. Temperatures and atmospheric pressures fluctuate at a similarly slow pace, which is obviously far from the audible spectrum of roughly 20 tot 20000Hz. So how can one turn these periodically changing parameters into sound or music, how can a 'sonification' be done? Bob Sturm knows. Without going into the technical details, the process is easy to understand. First, select a suitable buoy in the ocean, for example somewhere off the Californian shores of the Pacific. 'Suitable' means that the data about the buoy's position, the direction of movement of the wave peaks and the ambient atmospheric parameters taken at regular intervals of at most a few milliseconds and over a significant stretch of time, should be available, preferably for free. Next, you look at these data through a 'window' of, say, 50 milliseconds and perform a spectral analysis (identify the amplitudes and periods of the sine waves that, superposited, describe the buoy's motion). You'll end up with a spectrum that is far removed from the audible range but with some imagination and a fast maths program like MatLab, it is possible to map the spectrum of the buoy onto the audible spectrum. Anything from a linear mapping by multiplying the spectrum v by 5000 to a more complicated mapping like f = 7exp(20-12.09(v+1)) will do, as long as the output f is somewhere between 20 and 20000 Hz. Now, with this newly calculated f, perform an inverse transform and lo and behold, an audible signal comes to life!

Of course, a lot of decisions have to be made along the way such as the window size and shape, the mapping formula, the format of the data to be sonified and the time compression. On this CD, the results of a wide range of choices in the sonification of the directional buoy number 045 at Oceanside, California are collected and explained. For example, tracks 22 to 24 let us hear the entire year 2000 in fast-forward: in 10, 3 and 1 minutes respectively. Impressive! How does it sound? 2000 was a rumble. To be sure, you can't hear an individual wave, but at the 'slowest' pace, a high pitched sound of about half a second represents a day of fast moving waves originating from a storm somewhere far out at sea, or so I like to think.

Bob Sturm has collected and explained 28 samples from his sonifications of buoy 045. Together with the very clearly written introduction, they give a fascinating insight in the processes involved in his work as well as a good idea of the sheer diversity of motion at the ocean's surface. Ocean, if you ever doubted, is more than 11 or 12 . . .

Tracks 29 to 34 are compositions and compositional ideas. With no other material than the sonifications of buoy 045 and its sisters, the artist/scientist 'paints' an uncanny but beautiful portrait of a Fall storm in 2001 and the "Foam and Froth of Faraway Storms". And who would not want to take a dip after hearing the composition named "SST-036200001, f' = f + 1000(sst/7.1 - 1)"?.

Bob L. Sturm has a BA in physics and an MA in computer music technology from Stanford. He is also the founder of Composerscientist.com, which he began after developing methods of sonifying and composing with ensembles of particles. Other examples of his research and compositions are at the website.