B4-C5. Moritz, Frederick. "A Dissertation on the Use of Alternate Fingerings for Some of the High Register Notes on the Heckel and Heckel-Type Bassoons." The Double Reed 8/3 (Winter 1985): 28.
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B4-C5. Timm, Everett LeRoy. The Woodwinds; Performance and Instructional Techniques. Boston: Allyn and Bacon, 1964, p. 177.
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Heckel-System (German) Bassoon Trills and Shakes by Note Names