The Musical Effect of a Unison Ensemble

Question

Upon reading sheet music for black spirituals, I discovered something unusual:

As you might notice, the bass, tenor, alto, and soprano parts are all singing the exact same notes throughout the majority of the melody (with the exception of the chordal ending phrase). Since choral arrangements usually divide vocal parts for harmonies, counterpoint, etc., what is the significance of aligning vocals from different registers?

Is there an implied direction for the unison singing to produce various, contrasting notes, or perhaps, does the effect of unison singing emphasize the one melody (in which case, does it even matter if only person sings it)? I'm looking for a more theoretical/philosophical answer, and would be happy to hear what you guys make of this.

Answer 1

There's some phisical consequence in two or more voices/instruments producing the same note (besides the somewhat obvious volume raise). See, notes (higher or lower) depend on their frecuency (amount of vibrations per seconds, measured in Hertz(Hz)). A group may try to sing the same notes, but the tiny fluctuations and minimal down-tunning or up-tunning will lead to a phisical phenomenon known as (in spanish, pardon my ignorance of the english word) 'batimento', which means something like 'tapping' or 'rattling'. This is the result of somewat similar waves sometimes cancelling and sometimes boosting each other, several times per second. This makes the whole gain richness and expresiveness.

It's also what the electronical effect known as 'chorus' tries to resemble: 1) The signal is doubled 2) The copy is detuned slightyly (in a fluctuating fashion, in turns) 3) Both signals are played toghether.

There's a good explanation here: http://en.wikipedia.org/wiki/Chorus_effect

Answer 2

This style of singing is actually seen more common than you would think. You can hear it in hymns, national anthems, and even Happy Birthday. The idea is that everybody singing the same note will sound like one powerful voice and has a different texture then if the 4 parts had different notes.

This piece seems to start like most hymns do with many voices sounding like one, but at the end the voices are in 4 part harmony to empathize and give a more "heavenly" sound to the last few measures of the song.

Answer 3

I believe that spiritual you posted should be interpreted exactly as written. It doesn't imply that the singers should harmonize or that only one person should sing.

This is simply because the sound of one singer and the sound of a group of people singing the same thing is Just Different. I would expect a lone singer to be used most often to portray intimate, vulnerable, raw, or sorrowful emotions, while a group singing in unison would be more often used to portray an emotion that is forceful, overwhelming, majestic, epic, or threatening. Going from multiple singers in harmony to multiple singers in unison, especially in the example you posted, would emphasize the melody in a way that is somewhat more intimate than the harmonized melody without sacrificing much forcefulness.

Answer 4

As well as Marcos' idea of beats - where voices will be very slightly out of tune, especially when there are many, and different octaves are sung, there's the effect of vibrato. Each individual's voice has its own speed of vibrato, so the blend of many voices will have a rich sound with both phenomena working.

Answer 5

In addition to the beating (or "chorus") effect from singing/playing in unison that other answers mention, there is also an effect produced by singing/playing in octaves. This creates the effect of making the sound "bigger" (I'm not sure how else to describe it). This is not just the same as louder -- the effect even occurs when the parts are played very quietly. I assume the effect is caused by the higher-octave instruments reinforcing the higher harmonics of the lower-octave instruments.

This effect is frequently used in orchestral settings. Especially, for example, when cellos and basses play the same line octaves, to provide a reinforced bass line. It's also used when the strings or winds are playing a melody that needs to be heard over the brass.

One striking example that comes to mind is the opening note to Mahler's first symphony, where all the strings are playing the same note very quietly, across a large range of octaves, creating a lush, but still very soft effect.