Musica Instrumentalis, Video II (B), Video II (C), Video II (L)
The audio–video generating source is a single “stereophonic” musical instrument capable of producing sustained sounds. Such a stereo instrument will have two or more sound–producing elements separated in space, as in pipe organ installations. Spatial distribution of sound is necessary for the production of phase differences between the x and y signals. The types of images obtained on the screens of the converted television sets are dependent upon the harmonic content, amplitudes, frequency ratios, and phase differences of the signals generated. The instrument used most often for Musica Instrumentalis was the bandoneon, as performed by David Tudor (1926–1996), to whom I dedicated the piece. The sets of reeds of this instrument are physically separated, and the bandoneon’s performance conditions involve movement of the sound–producing elements in space—an especially attractive feature for the acoustical generation of variable phase relationships between the microphones. Other very useful phase shifts occur from intervals of the octave, unison, and fifth, where slight mistunings are present. If stationary or non–stereophonic musical instruments must be used, the addition of a variable phase–shift network in either the x or the y channel is recommended.
At least two performers are required: one to play the musical instrument and one (or more) to operate the electronic equipment. During the performance, the players are encouraged to move the instrument and microphones about gradually and to produce varying types of audio feedback. Visual feedback between the performers and the television screens is a continuing process throughout the duration of the piece, which can be brought to a satisfactory conclusion if at least one of the score images has been exactly reproduced. The sounds of the piece are a by–product of the visual feedback process.
The electronic configuration for Musica Instrumentalis is shown in the performance schematic diagram. At least one monochrome and one color television set should be used, but more are recommended for large audiences. The setup for Video II (B) and Video II (C) is recommended initially as a test for the system and as a means of acquainting the performers with the properties of the audio/video interface. Maximum channel separation must be maintained at all times between x and y signals, otherwise, uninteresting diagonal linear displays, instead of two–dimensional ones, will be seen on the cathode–ray screens. The convergence circuitry of color television may be disconnected if the inherent convergence deflection modulation is considered undesirable. RF signal generators or direct connections to the video inputs of monitors are optional; these are convenient applications for obtaining z–axis modulation. Connections to the r–y and b–y amplifiers of color television are necessary to preserve color synchronization.
Note: Extreme care must be taken in the presence of exposed high–voltage television components during testing and performance.
Video II (B) and Video II (C)
These pieces may be performed separately, together, or with Video II (L). Two–channel audio recordings are available from this web site.