What one-octave set of notes is most comfortable for an SATB choir to sing in unison/octaves?

Question

I'm scoring a piece for SATB choir and there is a moment that I want a melody sung in unison/octaves by the whole choir. The melody spans an octave. I first conceived of the melody in A minor, where its range spans from E to E. This would be perfectly fine for soprano and tenor, but sits too high for alto and bass. But if I transpose the melody down much lower, the sopranos and tenors begin to bottom out their ranges. I know that it will not be perfect.

What range for a one-octave melody is likely to be most successful and least uncomfortable for the singers in a standard SATB choir? Are there examples in the literature that use choral unison/octave over a range this large?

I would rather not ask any voice part to change octave halfway through.

I'm thinking spanning from C to C is the most attractive option. That notion is supported by this question (link), which mentions the same range but for amateur singers instead of trained musicians. If it matters for this question, the choir is auditioned, professional ensemble.

Answer 1

What range for a one-octave melody is likely to be most successful and least uncomfortable for the singers in a standard SATB choir?

It depends largely on the dynamic level and character of the melody. If you look at the ranges in this PDF survey of orchestration texts (found in a comment on the question Accepted ranges for SATB choral works?), you will see that the upper limit for altos and basses is around D5/D4 (with a lot of variability from one source to another) and the lower limit for sopranos and tenors is given anywhere from A3/A2 to D4/C3.

So depending on which authors you choose to believe, you could go anywhere from A to D. But look, you don't want basses and altos trying to sing the upper D quietly, and high sopranos are not going to have much to give below the lower D, certainly not loudly. So if it's a loud passage, I'd go for D or D♭. If it's quieter, lower will be better. I have known quite a few sopranos and tenors who are unhappy down there, so I would not go below C or maybe B♮.

The choice of pitch with also depend on tessitura. If the melody stays near the top of its one-octave range then you'll want to choose a lower pitch, and the converse is true as well.

Aaron's idea of having the basses two octaves below the sopranos is intriguing, but I'm unaware of any examples of this in the literature, and I suspect that you would have pervasive balance problems with the sopranos near the top of their range and the basses near the bottom of theirs.

Are there examples in the literature that use choral unison/octave over a range this large?

Well the first that springs to mind is Handel's Hallelujah chorus, which has the initial statement of "for the lord god omnipotent reigneth" in unison. It's in D major. The sopranos start on A4, ascend stepwise to D5, drop an octave and then back up, then descend stepwise to A4. The basses and tenors double them an octave lower. (The altos sing the first note in the soprano octave and then jump down to join the men, except for the low D, but this is possibly because many of them were men singing in falsetto). Note that this music was probably performed around a half step below modern pitch.

There are quite a few passages in octaves in Beethoven's 9th symphony, including a few where the basses are two octaves below the sopranos, I just learned. The ninth is notoriously difficult to sing, so take it with a grain of salt, but it will be helpful to have a look at it.

There's also a brief passage in the Dies Irae of Verdi's Requiem, starting (ppp) on a low B♭, but it doesn't span an octave.

Answer 2

B♭ to B♭ is safe for all voices.

Answer 3

TL;DR: Write C-D(+oct), with sopranos and altos in unison on octave above the unison tenors and basses.

---

The accepted answer to What are the typical ranges of voice types? gives the following as the most comfortable ranges (tessituras) for each vocal part:

S: A4 - G5
A: D4 - C5
T: A3 - F4
B: E2 - G3

The overlap, without regard to octave, is either E to F (a minor second) or A to C (a minor third)

S-A overlap = D-G or A-C (fourth / third)
 -T overlap = D-F or A-C (third / third)
 -B overlap = E-F or A-C (second / third)

Obviously, this is insufficient.

Looking at the wider, standard range for each voice, we have (from the above-linked post):

S: C4 - G5
A: G3 - D5
T: C3 - G4
B: D2 - C4

Now the overlap (disregarding octave) works out to be:

S-A overlap = C-D(+oct) or G-G(+oct) (ninth / octave)
 -T overlap = C-D(+oct) or G-G(+oct) (ninth / octave)
 -B overlap = C-D(+oct) or G-G(+oct) (ninth / octave)

Thus, the overlap areas, mapped back to each voice's range, are:

S: C4 - D5 or D4 - D5 or G4 - G5
A: C4 - D5 or D4 - D5 or G3 - G4
T: C3 - D4 or D3 - D4 or G3 - G4
B: C3 - D4 or D2 - D3 or G2 - G3 (see note)

Notes outside these ranges will either be too low or too high for at least one vocal part, unless the part suddenly changes octave.

Finally, G-G is not ideal, because (as @the-baby-is-you points out in the comments) the high range is likely to be difficult for mezzos, baritones, or untrained singers, and the sopranos will tend to stick out in the texture, being one or two octaves higher than the other voices.

Conclusion: the best range is C - D, with alto-soprano and tenor-bass unisons.

---

Note: Wikpedia, via The New Grove Dictionary of Opera, cites the bass range as E2 - E4. My own experience is that E2 is comfortable for basses, but D2 is too low for some, so D3 - D4 might be the better range. Also, as @phoog points out, it would be more typical to have the basses one octave below the sopranos rather than two.

Answer 4

I’d advice to not have the sopranos and tenors go below a C4/C3, and to not have the Altos and Basses go over C5/C4. But also keep in mind that if you have the voices unisono the Altos can compensate for the sopranos in the low range, while the sopranos can compensate for the Altos in the high range (similar with the Tenors and Basses). So in the high range the Altos and Basses can try to sing as soft as possible or even stop singing at all.