Around this time next year will be the centennial anniversary of the first performance (June 23, 1920) of Gustav Holst's First Suite in E-Flat, one of the most well-known works written for wind ensemble. The first movement is a chaconne. The repeating chaconne melody is on the first line below: octave position may vary for all the melodies in this example. After nine statements of this melody, the chaconne is diatonically inverted to start also on E flat—shown as the second melody below—and presented twice as such. Next the third melody below—a diatonic transposition of the chaconne to start on G—is presented once, followed by a restoration of the original chaconne tune. (I am ignoring the last statement, which deviates from the three-flat collection.)
Octave aside, there are six other diatonic transpositions and seven diatonic inversions of the initial chaconne melody. The second and third melodies above are only one of each set. Why choose them, of all possible? There are many ways to answer this question. Here's one. The F-Bb succession in the original chaconne melody, highlighted with blue brackets, clearly expresses dominant function at the end of its two halves. An alternate way to express dominant function using the same diatonic interval class (fourth or fifth) is with the tritone. In the key of E-flat, the tritone is between D and Ab, highlighted with green brackets. The second melody above is the only inversion that replaces F and Bb with D and Ab. (Holst deviates from the second melody's inversion by ending on G instead of Ab—hence the dashed green bracket—but nonetheless delivers ^2 and ^5 just like the original melody, but in C minor.) Likewise, the third melody above is the only transposition that replaces F and Bb with Ab and D.
The second and third melodies are related by inversion around F. (There are many ways to recognize this: F is equidistant between the starting notes of Eb and G, and it is equidistant between the notes D and Ab, a dyad that inversion around F preserves.) The three-flat collection, such as E-flat major or C minor, inverts into itself around F, as shown above. This means that a melody in a three-flat collection that is inverted around F will maintain the same major and minor qualities of intervals. The figure above places a letter that shows the quality of each melodic interval above it: m = minor, M = major, P = perfect, A = augmented, d = diminished. The purple enclosure surrounds intervals in corresponding spots in melodies that express the same major or minor quality of seconds and thirds. This L-shaped enclosure demonstrates not only that, as aforementioned, the second and third melodies use the same quality of seconds and thirds in corresponding positions, but also that the first melody inverts these qualities exclusively in its first part, and matches them exclusively in its second.
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