Decorated Cantus FirmusBach uses the chorale O Mensch, bewein' dein' Sünde groß (O Man Lament Your Grievous Sins) in one of his grandest cantus firmus works, the opening chorus of the St. Matthew Passion. Study his "simple" chorale setting in preparation for hearing its its decoration in a chorale prelude.
The first six pitches of the cantus firmus are do-do-re-mi-re-do as represented in the following comparison. In one more of the chorale preludes from the Orgelbüchlein, Bach uses 32 notes to decorate these six pitches! He continues in the same manner to adorn the entire melody. If you did not know the chorale tune well you might have trouble recognizing that this decorated version has any relationship to the original. Stein calls this type of chorale prelude "chorale as aria" (p. 148). Other writers classify it as chorale fantasia. But I like to call it "decorated cookie."
Now listen to the complete chorale prelude while following the chorale score. Can you pick out the pitches of the cantus firmus in the decorated version? Notice that O Mensch bewein is in German bar form AAB. Is the "A" section decorated the same in its repeat as the first time through?
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©1996 Timothy A. Smith
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