David Rosenboom is an American composer. He studied electronic music at the University of Illinois at Urbana-Champaign among the likes of Kenneth Gaburo and Lejaren Hiller. He worked alongside Don Buchla and is considered one of the first composers to use a digital synthesizer, though I think Jon Appelton's works for the Synclavier synthesizer probably predate Rosenboom's digital works. He was also a pioneer in the use of neurofeedback and compositional algorithms as exemplified by Brainwave Music. These notes, taken from the back cover, describe the methods used to create "Portable Gold and Philosopher's Stones (music from brains in fours)" -
"Electrodes and appropriate monitoring devices are attached to monitor the brain waves of four musicians who have been well rehearsed in the voluntary control of their pyschophysiological functions. Monitors are also attached to two of the performers for body temperature and to the remaining two for galvanic skin response. This information is all fed into an analyzing system that extracts such things as, percent time per mint spent emitting Alpha brainwaves, average time spent emitting Alpha, the amount of variance in the amplitude of Alpha, the coherence time of any patterns discovered in the brain wave, correlations between brainwaves or two or more performers, relative entropy of the waveforms, relative intensity of various spectral bands in the brain waves, etc.
A sound producing system is set up as follows. Four frequency dividers, capable of producing pulse waves that are some integral division of a sine wave frequency being fed to all four, are set up. These dividers are capable of producing exact pitch ratios that are a function of some control voltage, in this case, voltages from the monitors of skin temperature and galvanic skin response. The resultant precisely tuned chord of pulse waves is fed, then, into a bank of voltage controlled resonant band pass filters, called a Holophone. Relative amplitudes of the filters' outputs can be programmed. The result analysis of the performers' brain waves is directly applied to the voltage control inputs of the filters. The relative output amplitudes of the filters are controlled by signals deriving from a Fourier analysis of the brain waves.
When two of more pulse waves of exact pitch intervals are applied to a resonant band pass filter, the filter can extract the harmonics present in the waveform composite. A particular intercal will then produce a set of extractable harmonics that forms a mode. The music proceeds as an improvisation within these modal possibilities.
The technician's part lies in the modes of analysis of the brain waves he uses and their application as control for the sound producing system."
Well, that's quite a bit to process. It all makes for highly enjoyable music, though. The piece described above is essentially an 18:30 long drone of various harmonics and waveforms that shift, incidentally forming harmonies and dissonance. The composition that follows, "Chilean Drought", features three vocalists who recite individual texts. Each vocalist represents either Beta, Alpha, or Theta brainwaves and recites their text as their assigned wave arises from the control performer. The vocalists are accompanied by piano for melodic cohesion. The final composition, "Piano Etude I" utilizes a piano passage taken from another composition amusingly titled "How Much Better If Plymouth Rock Had Landed On The Pilgrims." The passage is played fast and is intended to be complex and repetitive, requiring endurance. Rosenboom was interested in the relationship between Alpha wave production and intense motor tasks. The rapid brain signals produced when performing modulate center frequencies of two band rejection filters that have the piano sound as their input. This results in random, fluttering pulsations that, as he puts it, "place a mask over, or carve a hole in, the block of piano sound."
Download it here.