Thickness or thinness can be regulated and varied by increasing or reducing the number of voices. A too thin scoring, too long continued, becomes disappointing. A scoring with too many voices, too long continued, becomes wearing. Structural eventfulness is dependent upon a balance between these two extremes. Such a variegation of thickness and thinness can be
applied to any of the textures. Even a monophonic texture can be thickened by adding octave doubling, or thinned by reducing the sonority to a single line. Sudden change from thick to thin brings about a feeling of relaxed clarity and pleasant surprise. Sudden change from thin to thick brings both surprise and excitement (as in the overtures of Weber). Debussy creates crescendi and diminuendi by gradually adding or taking away various instruments.
In general, however, the problem is to create a relaxed variety of thickness and thinness of texture that is fitting to each kaleidoscopic change of musical mood. The Brandenburg Concerti by Bach illustrate the application of such variety to polyphonic texture. In certain movements of these concerti the rhythmic and motival unity is so intense that variety through light and shade is a natural necessity; Bach takes advantage of this organic need by creating a marvel of “cameo-like” variation in the number of voices.
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