INSTRUERE by David B. Doty

The subject of this edition of Instruere is David Rosenthall composer, instrument builder, and freelance percussionist. A versatile performer, David has appeared with a variety of local ensembles, including the San Francisco Percussion Ensemble, which he co-founded with Rick Kvistad in 1977. His own works, many of which involve his unique percussion instruments, have been performed recently at the Cabrillo Festival, at the San Francisco Art Institute (during the "Forms for Sound" exhibition/performance series) and at the Exploratorium.

David's major instrumental creations to date comprise two large percussion instruments: "The Tubes," a metallophone with keys of 7/8 inch outer diameter "Cyprus" conduit tubing over clear acrylic resonators, and a "Justly Intoned Marimba" of pernambuco wood blocks. The tuning of these two instruments is an expansion of harry Partch's tonality diamond idea. The principle of the tonality diamond derives from Partch's belief that, in a system of just intonation, Major and minor tonalities coexist on an equal basis; major being derived from the harmonic series, (f, 2f, 3f, 4f, . . . ) and minor from its inversion herein called subharmonic (f, f/2, f/3, f/4...). Using each successive degree of a harmonic series as the starting point for a subharmonic series (or vice versa) results in the creation of a fabric of interwoven tonalities which is theoretically capable of infinite expansion. (Diagram).

acting on this idea, Partch created the "Diamond Marimba," an instrument with a diamond shaped keyboard on which diagonal sweeps produce arpeggiated six-note chords (hexads) consisting of the odd number degrees of a series, through eleven; harmonic or subharmonic depending on the direction of the sweep. David Rosenthal's instruments, while based on the same principle, are quite different in design. Each has eight distinct banks of eleven keys, each bank consisting of the odd degrees of a series, through fifteen, plus octave duplications. (In an harmonic or subharmonic series, each successive odd number is a new pitch, while each even number is the octave duplication of a previous pitch.) The marimba has harmonic (major) tonalities built on each of eight odd degrees of a subharmonic series (within one octave). The Tubes consist of eight subharmonic (minor) tonalities built on the odd degrees of a harmonic series (also within one octave). Thus the two instruments are complimentary, having the same pitch material arranged in different patterns. Intended primarily for accompaniment, these instruments are able to provide chordal support for a great variety of just scales. That they can also function in the foreground is amply demonstrated by Rosenthal's piece "Perpetual Motion," which treats the entire tonal fabric of the marimba as a mode.

Recently David has turned his attention to composing for various small ensembles of stringed instruments such as the bowed psaltery, hammered dulcimer, harp, and viola. His works for these instruments utilize an ancient Greek seven tone scale, the Didymus Chromatic, in various permutations. Featuring lively dance-like rhythms and transparent counterpoint, these pieces suggest a combination of medieval polyphony and Appalachian music, with an occasional suggestion of the blues. David is particularly intrigued with the resources of the bowed psaltery and has ordered several from a local maker to use for different tunings. (Such instruments do not stay in tune well if their tuning is altered frequently.) He is currently working on a piece which will combine the psaltery, viola and dulcimer with the Tubes and marimba.

David's attitude toward instrument building could be described as pragmatic. While he takes justifiable pride in the instruments he has built, he considers his time best spent in composition, and would willingly employ professional craftsmen to execute his instrument designs, were it economically feasible. His plans for the future include a modular marimba in which each key with its resonator would constitute a module. A number of these units would be assembled in a frame and held in place, perhaps with Velcro, to make a scale. This instrument, having only the notes needed for a given composition, would facilitate certain rapid styles of playing which are difficult to achieve on the larger instruments with their vast tonal fabric.