On Jan. 21, the Boston Microtonal Society presents a concert including an American classic, Ben Johnston's String Quartet No. 4, "Amazing Grace," composed of variations on that hymn's standard tune. Written in 1973, the Fourth Quartet is easily Johnston's best-known, most-heard work, despite (as Johnston himself has wryly noted) the music's rigorous and pervasive technical nature — or, perhaps, because of it, a zealous theoretical integrity manifested, in performance, as confident conviction. In that, it keeps remote faith with the hymn at its core.
The basis of the Fourth Quartet is just intonation tuning, which Johnston has assiduously explored for most of his long career. (He will celebrate his 90th birthday in March.) For centuries, Western classical music has been oriented around equal temperament, a purposeful homogenization, allowing modulations between far-flung key centers without one sounding more off-key than the other. But equal temperament is a series of compromises — every key is rendered equally out-of-tune — muddying the simpler ratios between the frequencies of natural musical overtones. Just intonation restores those purer intervals; the opening of the Fourth Quartet, for instance, uses a scale based on stacks of pure fifths, in 3:2 ratios.
Yoked to "Amazing Grace," such tuning sounds both unexpected and deeply familiar; string players and singers, especially, routinely inflect their intonation toward such purer intervals. The quartet's opening seems to expand the rustic sound of open-string fifths until it permeates the entire texture. Later, when Johnston brings in intervals derived from the seventh partial of the overtone series, it is like the distilled essence of a blues scale. But the values of just intonation inform every aspect of the work, ratios rhythmically translated into complex, fluid layers of competing speed, differences between the frequencies of successive notes of a scale governing an irregular succession of downbeats. Almost everything in the piece springs from a common mathematical basis.
The hymn "Amazing Grace," originally conceived to illustrate undeserved reward (John Newton, the author, placed it in the biblical context of God's promise of blessing on King David's descendants), came into prominence during the Second Great Awakening, the early-19th-century religious revival marked by Methodism: rejecting the Calvinist doctrine of predestination, instead preaching deliverance through good works and conscientious, pious living. Johnston's quartet, similarly, finds salvation not in mysterious inspiration, but a scrupulous, thoroughgoing application of musical ideals. The sweet sound of "Amazing Grace," appropriately, becomes a deceptively simple conduit for a sophisticated disquisition.
The Boston Microtonal Society, in association with the New England Conservatory Theory Department, presents "Amber: A Concert of Microtonal Music for Strings and Flute" on Jan. 21 at 8 p.m. in NEC's Pierce Hall. Free admission; necmusic.edu/event/14868