Range

Sing the lowest note you can, then the highest. Everything between those two is what your voice can do; below and above them, nothing comes out. Every voice and every instrument has limits like these, and the set of notes between them, from the lowest to the highest, is its range (Lacerda 1966, ch. XXXVI).

A soprano, for example, normally sings any note from the C below the treble staff up to the G above it (Lacerda 1966, ch. XXXVI).

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Writing a range down

A range is not a melody, so there is no point writing every note in it. The two ends are enough: the lowest note and the highest, usually in whole notes, often joined by a diagonal stroke. Everything in between is understood.

In Lacerda's table of adult voices, a bass goes from the F below the bass staff up to middle C (Lacerda 1966, ch. XLI).

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A melody has a range too

The same idea applies to a piece of music. The range of a melody is the set of notes it covers, from its lowest to its highest (Lacerda 1966, ch. XXXVI). It says nothing about the order of the notes, only how far the melody spreads.

Take the opening of "Twinkle, Twinkle, Little Star":

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The lowest note is C and the highest is A. The rest of the song never leaves that space, so its whole range is a sixth:

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That small span is part of why children sing it so easily. At the other extreme, "The Star-Spangled Banner" spans an octave and a fifth, and many people run out of voice at the top of it.

Not every note is equally easy

The ends of a range are limits, not comfortable places. Near the bottom, a voice loses strength; near the top, it strains. Most of the time, a singer is at ease in a narrower band in the middle.

The limits are not fixed, either. Blatter gives the ranges of the four voices for untrained singers, marking a normal range and, beyond it, notes that turn up only occasionally. Trained singers go further, and many amateurs manage only part of the span (Blatter 2007, part 4, art. 1). Lacerda agrees that a singer who works on vocal technique can extend their range (Lacerda 1966, ch. XLI).

Why it matters: choosing a key

Range is the first thing to check when someone is going to sing a melody. If the melody goes past the range of the voice, it cannot be sung as written.

Suppose a melody runs from E on the bottom line of the treble staff up to the E an octave above. For a soprano it is ideal: that octave is exactly the part of the voice Lacerda marks as the easiest to sing. For a contralto, whose range he places from the F below middle C up to the C in the middle of the treble staff, the top goes too high (Lacerda 1966, ch. XLI). Moved down a major third, from C to C, the same melody fits.

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Moving every note of a piece up or down by the same interval is transposition. Blatter gives this very case: a song written for sopranos is too high for altos, so it is transposed into a lower key (Blatter 2007, part 6, app. V).

One idea, several words

The names for range vary more than the idea does.

In English, range is the span from the lowest to the highest note. Ambitus is often used for the range of a melody, especially in chant. Tessitura usually means something narrower: where most of the notes of a part lie, or the stretch of a voice that is comfortable.

Portuguese books use the words differently. Lacerda calls the whole span tessitura, and gives the comfortable middle part a name of its own, registro médio (Lacerda 1966, ch. XLI). Med treats tessitura, âmbito and extensão as synonyms for the set of sounds a voice or instrument can cover (Med 1996, ch. XXXVIII). So a Portuguese text that gives a singer's tessitura is usually giving the full range, not only the comfortable part.

What comes next

Range can also tell apart two melodies that use exactly the same notes. In the old church modes, a melody ending on D with the notes of the Dorian scale is authentic or plagal depending only on where its range lies around that final: mostly above it, or spread on both sides. That is the subject of authentic and plagal modes.