|Duoi contrabassi de Viola|
|Dieci Viole da brazzo||
10 viole da braccio [early viola]
|Un Arpia doppia
|Duoi violini piccoli alla Fancese||
2 small violins [French violins]
|Duoi Organi di legno|
|Tre bassi da gamba|
|Quattro Tromboni||4 trombones|
|Un Regale||1 regal (For German speakers, this is a picture from the Organ Museum in Germany)|
|Duoi Cornetti||2 cornetts [zink]|
|Un Flautino alla Vigesima seconda||1 recorder [soprano]|
|Un Clarino con tre trombe sordine||
4 trumpets, muted [natural, no valves]
The following note is from "L'Orfeo: Monteverdi," by Sophie Roughol, translated by Claire Fontijn. Goldberg Magazine, 4. (http://www.goldbergweb.com/en/magazine/essays/1998/09/176.php)
The title page of the first edition of L'Orfeo seems to indicate quite precisely the orchestration necessary for performance: “Duoi Gravicembali, Duoi contrabassi de Viola, Dieci Viole da brazzo, Un Arpia doppia, Duoi violini piccoli alla Francese, Duoi Chitaroni, Duoi Organi di legno, Tre bassi da gamba, Quattro Tromboni, Un Regale, Duoi Cornetti, Un Flautino alla Vigesima seconda, Un Clarino con tre trombe sordine.” One can say that in terms of instruments, Monteverdi used the complete palette of sonorities available to the Renaissance band and the first fruits of the Baroque. But if he is relatively precise at the outset, with respect to indicating which instruments are to play at what moment, in the rest the composer is not. What's more, the preliminary list seems incomplete. At the beginning of the third act, in Hell, he specifies that cornettos, trombones, and regal are to enter, which presumes that they were excluded prior to that.
In fact it seems clear that their use was instituted in modern interpretations, and that two groups of instruments were used for the two principal scenes of the work—cornettos, trombones, and regal for Hell, violins, harpsichords, lutes, and flutes for pastoral scenes—two groups to which it is suitable to add trumpets for the introductory fanfare. The care taken to differentiate between the sonorous decor of each world can even be found in the vocal timbres: the pastoral choruses are for mixed voices, while the choruses in Hell are reserved for somber male timbres (it's well known that there are no women in hell!). Certain instruments merit particular attention, such as the organo di legno, an organ whose wooden pipes produce a very soft timbre, which notably accompanies Orpheus's mourning after the death of Eurydice. At the opposite end of the spectrum stands the regal, an organ with vibrating brass reeds, which produces an aggressive, sarcastic sound, ideal for accompanying a character like Charon. The arpa doppia required by Monteverdi is a harp with two or three rows of strings (allowing for accidentals), generally used from 1600 onward as a continuo instrument, but here raised to the rank of virtuoso soloist.
The instrumentation of L'Orfeo once again raises the issue of fidelity to the sources of interpretation. On one hand, some of Monteverdi's indications have to be respected or one risks misinterpretation, especially those linked to the expression of textual affect. But on the other hand, the continuo—for which the composer left no precise indications—should obey the principle of improvisation, strengthening the bass line and inventing the middle voices. The work of interpreters today presupposes as much knowledge of theoretical sources on basso continuo realization as of dramatic intelligence. Not to mention acoustical problems, for few contemporary halls can boast the same acoustics as the gallery of the Mantuan ducal palace!