in B-flat major for 2 violas de braccio, 2 violas da gamba, violincello + continuo (violone and cembalo)
The last of the Brandenburg Concertos is often considered the oldest, as its instrumentation conjures a 17th century English consort of viols, similar scoring had been used by Bach in his earlier Weimar cantatas, and its structure relies heavily upon both the ancient canon form and the conservative Baroque gesture of a chugging bass of persistent quarter-notes.
A viola da gamba
Yet, typically, Bach combines a knowing salute to the past with a bold leap into the future, raising the violas, customarily embedded in the continuo accompaniment, to solo status. The unprecedented gesture was triply suitable – the viola was Bach's own favorite orchestral instrument (as he once put it, placing him "in the middle of the harmony"), it was also the instrument played by his patron Prince Leopold, and the Margrave's orchestra was known to have employed two especially accomplished violists.
Scholars assume that Bach only had enough forces at Cöthen for one player per part. Indeed, performances with full string sections, or even large chamber ensembles, no matter how well rehearsed, tend to blur the precisely articulated interplay of buoyant rhythms and swamp the harpsichord, whose bright plucked overtones need to emerge from the depth of the strings. Moreover, the nasal sound of violas da gamba (six-string bass viols held between the legs) and a single violone are needed for bright, transparent middle and bass lines that complement rather than thicken the tone of the featured violas de braccio (hand-held violas comparable to current ones) and solo cello. Similarly, modern substitutions of deeper and more powerful modern instruments, including a double bass, unduly deepen the sonority and fuse the timbres.
In one sense, the work seems a concerto for two violas to display Bach's love of his instrument and its full range of expressive possibilities. Yet, it is their interplay, both with each other and with the cello and continuo, that characterizes each of the three movements, thus exemplifying the claim of Johann Nicolaus Forkel, Bach's first biographer, that Bach considered the essence of a polyphonic composition to be a symbolic tonal discussion among instruments, each presenting arguments and counterpoints, variously talking and lapsing into silence to listen to the others.
Shorn of the violins' customary brilliance, the dark timbre suggests a harbinger of the mystery and somber thoughts of the Romantic era to come. Indeed, Boyd sees the instrumentation as an allegory of progress, as Bach elevates the then-newest member of the string family to prominent status while relegating the older viols to the background. Yet Bach ingeniously creates a compelling and complex aural image of irresistible gaiety that arises out of and is enriched by its seemingly melancholy components.
The sections of the first movement are closely integrated into a continuous flow of vigorous thrust, led by the two violas in tight canon a mere eighth-note apart during each of the six ritornellos, blending into a lively dialogue with the gambas during the five episodes, all over a persistent quarter-note continuo rhythm. The second is a lovely, if somewhat quaint, meditation for violas and cello. The finale is an irresistibly propulsive dance in 12/8 time with astoundingly catchy primary and counter-melodies, in which Bach seems to tease us as the violas constantly begin, abandon and resume canonic imitation. Indeed, while Bach is reputed to lack humor, he manages to play an unintended joke on those of us relegated to listening on record – the violas constantly switch parts but the difference is inaudible and thus imperceptible without the visual clues in a concert. Perhaps out of respect for the limited stamina of his royal soloist, after sitting out the adagio, the gamba parts of the finale are easy accompaniment, leaving all the work to the violas and occasional fits of activity from the cello.
Source: Classical Notes