Giddins and DeVeaux on John Philip Sousa

"[T]he brass band … in peacetime became a local 'people's' orchestra. … The brass band's primary contribution to jazz turned out to be its compositional structure. The defining unit of a march is a sixteen-bar strain, which marries a dominant melody to an equally identifiable chord progression. Marches are made up of a series of strains, each usually repeated before passing on to the next. A typical march with four strains could be diagrammed as AABBCCDD or AABBACCDD (with the returning A offering a hint of closure and transition). No attempt is made to round things off at the end by reprising the first strain. The third or trio strain (C) is particularly significant. For one thing, it modulates to a new key (the subdominant, or IV), sometimes with the aid of a short introductory passage, and is often twice as long, lasting thirty-two bars instead of sixteen. Composers used the trio to change the piece's dynamics, texture, or orchestration. Many marches concentrate on the trio at the end, repeating it several times after dramatic interludes — among them Sousa's indelible classic, 'The Stars and Stripes Forever' [available on this recording]" (Gary Giddins and Scott DeVeaux, Jazz, pp. 64-65).