Trecho sobre Cori Spezzati no Le Istitutioni harmoniche (1558) – por Gioseffo Zarlino –

[x] representa o número da página da edição de 1968.

“[232]66. Some Advices about Compositions for More than Three Voices
(…)
[243]Psalms are sometimes written for the so-called split chorus (choro spezzato), which is frequently heard in Venice during vespers and other offices of the solemn feasts. The chorus is divided into two or three groups, each of which sings in four parts; they sing alternately, or simultaneously when it is appropriate. At the end it is particularly effective when they sing together. Because the choirs are located at some distance from one another, the composer must see to it that each chorus has music that is consonant, that is without dissonance among its parts, and that each has a self-sufficient four-part harmony. Yet when the choirs [244] sound together, their parts must make good harmony without dissonances. Thus composed, each choir has independent music which could be sung separately without offending the ear. This advice is not to be scorned; rather it is very handy and was formulated by the most excellent Adrian [Willaert].
Although this style presents some difficulties, one should not run away from them, because the results can be very admirable and excellent. These difficulties will indeed be minimized by a study of the learned [245] works of Adrian, such as the psalms “Confitebor tibi Domine in toto corde meo in consilio iustorum”, “Laudate pueri Dominum”, “Lauda Jerusalem Dominum”, “De profundis”, “Memento Domine David”, and numerous others such as the canticle of the Blessed Virgin “Magnificat anima mea Dominum”, which I wrote years ago for three choirs. To see and study these pieces will be of great value to all those who wish to compose in like manner. One will find, for instance, that the basses of the choirs always form unisons or octaves, or occasionally thirds, but never fifths, because they would cause difficulties and nothing good would be possible. The composer who stays within these limits will have much less difficulty in blending the parts of the choirs without dissonance.
Now, to conclude the discussion, let me say that the composer who understands all that has ben done so far must yet learn to organize the notes of his composition in terms of tempus, modus and prolation, the schemes under which his composition will be written. Because the schemes were once of great importance, and some still use them, I shall strive to give everyone an understanding of them. I shall cover only the essentials, ignoring what is cryptic and irrelevant. I shall begin with tempus, which is, I believe, the most universal and the principal of these.

ZARLINO, Gioseffo. The Art of Counterpoint – Part Three of Le Istitutioni harmoniche 1558. Trad.: MARCO, Guy A. & PALISCA, Claude V.. New Haven: W.W Norton, 1968.