Sums and Differences simulates a physical property: the action of energy (the sound of musical instruments) over matter (an image), this being created using a synthesiser. In the first sequences and first bars, the instruments are associated one by one with the sound that corresponds to them. Then the images of the instruments appear simultaneously, participating in the same passage of this electronic music. The orchestra is composed of a drum, keyboard and wind instruments. As the rhythm accelerates, the image becomes more complex and the whole ends in a cacophony of vision and sound. The work continues, as its title indicates, by the differentiation then the addition of space and sound.

Successive images undergo a multitude of transformations according to the rhythm of the sound: light-plays soften then heighten the contrasts, black and white are reversed in some sequences. The rhythm is slow at the start of the video and gradually increases, sounds intensify and the pictures change at every note, then overlap. The screen is divided into ever-increasing numbers of horizontal bars. When they are wide, fragments of instruments appear in some of them, whereas others are grey or black. For a brief moment, a wave spreads from one to the other. When they are narrow, the drum shows through in the background. These transformations are obtained by a technical process common to both sound and image, a frequency switcher - to quote Gary Hill's accurate description: "Normally, a video image is scanned on the video raster at 60 cycles per second. As the rates of change increase, starting at about one cycle per second, switching becomes faster than the time it takes to scan the complete image. This produces an effect whereby all four images appear simultaneously on the screen in 4, 8, 12, etc. horizontal bars. When the switching rate is at the higher frequencies, the different sounds, including the switching frequencies, become blurred into one, just as the different images become one image." [1]

By the creation and evolution of the image determined by a technical process proper to video, Sums and Differences is linked to the definition of the medium presented in Electronic Linguistic as being a set of luminous phenomena demonstrating an electrical energy.

Thérèse Beyler

[1] "Normally a video image is scanned on the video raster analyser at 60 cycles per second. If the switching rate is increased, starting at around one cycle per second, the switch becomes faster than the time needed to scan the entire image. This produces an effect whereby all four images appear simultaneously on the screen in 4, 8, 12, etc., horizontal bars. When the switching rate is on the highest frequency, the various sounds, including the frequency switch, are united into one, in the same way as images merge into one." (Lucinda Furlong, "A Manner of Speaking : an interview with Gary Hill", Afterimage, Rochester, Volume 10, Number 8, March 1983, p. 16)