Claudio Monteverdi (1567-1643) is the composer who best links the Renaissance with the Baroque periods and what was known as the prima pratica and seconda pratica, aka the “old style” and the “modern style”. The former emphasized clear, smooth polyphony as ordered by the Council of Trent and personified by Palestrina (the text was always to be understood), specified under what circumstances dissonances were to be used, and relied on the cantus firmus (fixed song) technique that was the backbone of Gregorian Chant. But he also made use of the stile moderno, which used monody — a single vocal line, sometimes highly ornamented, over a bass line played by lute, theorbo, organ, harpsichord, or a combination — the type of exclamation that was being used in opera, dance forms, and instrumental interludes. And none of his works exemplifies this connection, this perfect marriage, better than his Vespers of 1610.

The sheer variety of sounds and forms in the Vespers is staggering. The opening words are intoned by a soloist and these are answered by full chorus on one note, surrounded by the ornate brass fanfare Monteverdi used for the opening of Orfeo. The following Dixit Dominus has everything — dueling choirs, movements for soloists, simple monody that somehow transmogrifies into elaborate vocalizing; instrumental ritornellos for one piece contain 10 vocal parts and several instruments; the Lauda is polyphonic, the Sonata Sopra is an instrumental canzone, a simple chant by the chorus around which cornetts, sackbuts, and strings riff with different rhythmic and melodic strains.

A perfect example of seconda pratica is the psalm Nigra sum. A solo sings the text while a most ascetic basso continuo underpins the voice. But Monteverdi makes certain that the words are painted by the music: The word “nigra” means “black”, and the vocal line begins on low, long, dark notes presented in the minor key; “formosa”, meaning beauty (in reference to the Bride, or Virgin Mary), winds up in the major, is set higher, and is rhythmically appealing; “surge”, a call to “rise”, is sung to a melismatic rising vocal line. In “Duo seraphim” two angelic voices cry out; when the Trinity is invoked, a third voice, in imitation, joins them. The effects are playful, dramatic, and always surprising to the ear, introducing dissonances, soon resolved, which startle and entertain. The parts of Monteverdi’s Vespers are remarkable; the sum is both articulate and soulful.

The four-year old Green Mountain Project have made somewhat of a specialty of the Vespers, and their recent performance at New York city’s Church of St Jean Baptiste proved again that they are worthy of their chosen name. Under music director (conductor and first violinist) Scott Metcalfe, the 14 singers and 14 instrumentalists, with the cornettists doubling on recorders, offered a beautifully devotional reading.

Before each psalm, Metcalfe added a brief Antiphon (plainchant) for the First Vespers of the Feast of the Visitation, which falls on 2 July. The three men and one woman who performed the antiphons moved invisibly to different parts of the church; the listener was acoustically surprised each time they sang.

The various sections of the Vespers are, in themselves, celebratory – it begins with a dance, after all – but Metcalfe opts for a pious, rather than razzle-dazzle,approach. Although he encourages plenty of ornamentation, both vocal and instrumental, in the already wonderfully decorated music, he opts for relatively slow tempi and a certain simplicity of presentation. This can occasionally make the evening lose momentum; at the same time it allows the audience to hear the remarkable interplay among the various voices and instrumentalists. If the Duo Seraphim and Lauda Jerusalem lacked some joyfulness, the Pulchra es, on the other hand was as smooth, affectionate and worldly as it can be. The Nisi Dominus had a snappy, martial air to it; the Magnificat for seven voices was more contemplative – even the Gloria – than usual.

Aside from an occasional momentary flub – the tenor entry into Laudate pueri was in the wrong key and started over – and the Audi coelum, for two baritones at different ends of the church did not always find them precisely on the same note – the playing and singing were grand. Metcalfe goes for beauty of tone and gets it – his and second violinist Ingrid Matthews’ playing in the Sonata sopra Santa Maria was heavenly and the singers, in particular, spun out pianissimo phrases gloriously.

Green Mountain’s yearly programs, now part of a most welcome week-long early music festival, have become a grand occasion. May they thrive.