SATB Ranges, Spacing, and Voice Crossing

Four-part writing imitates a choir: soprano, alto, tenor, and bass each live in their own range, and on the grand staff each gets a fixed stem direction so you can tell voices apart at a glance. Soprano and alto share the treble staff, stems up for soprano, down for alto. Tenor and bass share the bass staff, stems up for tenor, down for bass. Spacing rules keep the texture sounding like a blended choir instead of a cluster or a gap: soprano to alto, and alto to tenor, must each stay within an octave, twelve half steps. Go wider and the two voices stop reinforcing each other and the chord sounds hollow on top.

The bass is exempt. It can drop a tenth, an octave and a fourth, even two octaves below the tenor without any penalty, because low pitches naturally sound farther apart to the ear than high ones. This is exactly why exercises look cramped up top and roomy at the bottom: the upper three voices are squeezed into overlapping octaves while the bass ranges freely underneath, often doubling the root an octave or two down.

Voice crossing is the other spacing issue: normally soprano stays above alto, alto above tenor, tenor above bass, and crossing those lines, even briefly, is avoided because it blurs which line is which. This topic sets up the physical geometry of a chord; the next step is spacing and doubling choices that keep each individual voice moving smoothly from chord to chord, which is where voice-leading rules about parallel fifths and octaves start to bite.