On a sheet of choir music, how do you interpret two notes represented by two heads on a single stem?

Question

On a sheet of choir music, how do you interpret a stem with 2 heads? For example, on the bass clef staff, who sings the note represented by the top notehead on the stem, and who sings the bottom one?

Example:

Answer 1

First of all, in your circled example the two note heads have their own stems, so they're not sharing a single stem.

You didn't provide the staff assignment. SATB hymn scoring (mostly homophonic) normally uses only two staves and the Bass-clef staff would be shared by the Tenor and the Bass. Or in a more contrapuntal SATB scoring (such as Handel's Messiah) each voice has its own staff (see sample For unto us a child is born). But in your score we have two voices per staff, so the scoring seems to be for SSAATTBB. The third staff seems to be for the Tenors because there is an 8 below the G Clef, indicating they are to be sung an octave lower. Therefore, the Bass-clef staff must be for Bass 1 and Bass 2, or for Baritones and Bass. (Thanks to @phoog I only later noticed that the snippet came from Anton Bruckner's Ave Maria, WAB 6 which is scored for SAATTBB, see full score here).

In a two-staves SATB choir notation, by convention the note stem pointing down would be for the Alto/Bass and the note stem pointing up would be for the Soprano/Tenor. Sometimes they overlap so the upper note whose stem pointing down is assigned to Alto/Bass. In your score, the notes with the stems pointing up are for the Baritone/Bass-1 and the the notes with the stems pointing down would be for the Bass-2. Similarly, for the other staffs, the notes with stems pointing up is for Soprano 1, Alto 1, and Tenor 1.

Measure 13 is instructive. You see one voice has a whole note E3 while the other voice has two half notes E3 and A2 with stems pointing down. This means the whole note is to be sung by the Baritone/Bass-1, while the half notes are to be sung by the Bass-2. If the Baritones/Bass-1 are to be the ones singing the half notes, the engraver would make the stems go up.

When there is only one note head+stem in the staff (see measures 30-38 and 43-47) most likely both Bass-1 and Bass-2 are to sing the note in unison, especially in this score where in measure 30 the last 2 quarter notes C3 are notated with both up and down stems, guiding subsequent measures' interpretation. When in doubt, of course you need to consult the choir director.

Answer 2

There are many possibilities, depending on the context.

If it is a four-voice choir written on two staves, there are two voices assigned to the bass-clef staff, typically tenor and bass. If there are no other notes or rests happening at the same time, then the tenors take the upper note. However, with a staff that bears two parts it's more common for one part to have stems always pointing up and the other always pointing down, so they would not share a stem.

Therefore, it's more likely that this indicates divisi. If it's the bass staff then typically the baritones (a.k.a. bass I) would take the upper note and the basses (a.k.a. bass II) the other. If the baritones are already on a separate staff then this could mean that the second bass section must itself divide, in which case one just has to assign people to one note or the other.

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Now that you've added an image:

The notes with stems pointing up are for the first basses, a.k.a. baritones. Those with the stems pointing down are for the second basses. In measure 13, the whole note has no stems, but because the half notes' stems are pointing down, you know that the whole note goes to the baritones.

Answer 3

It’s a divisi, meaning that the singers of that part divide their section into two.

In most choirs, the part assignments will already have been made within each section. The Tenors, for example, will already have been assigned Tenor 1 and Tenor 2 roles, based on whose voices skew higher (Tenor 1) or lower (Tenor 2), so that when a divisi comes up, they know which note to sing. The director might make adjustments — asking a few T2s to sing T1, say — to accommodate the musical needs of a particular piece.

A decision that goes along with the division of parts is how to distribute the singers standing position within the group. A few common ways:

• Every other singer: this produces an even, blended sound through the section, but leaves the four SATB sections distinct.
• Left and right: a common arrangement of voices will have lower voices on the left, higher on the right. Maintaining, the divisi voice would just be split down the middle.
• Even distribution: Rather than grouping the singers by vocal section, the sections can be mixed such that within the choir there would be one singer from each section next to each other. This provides a highly blended sound, but requires singers who can hold to their part without being next to someone singing the same part.