Composing for the inauguration of a harpsichord he had acquired in Berlin, Bach prepared the Brandenburg Concertos in 1720.  Drawing from a wide range of musical influences and styles, Bach pays tribute to and in many ways surpasses the works of his contemporaries, ultimately and undeniably furthering the concerto form. The concerto is a genre of instrumental works of three movements performed by one or more solo instruments accompanied by an orchestra.
In a musical context, the term “concerto” (from the Latin concertare; “to contend, to dispute, to debate” and “to work together”) was initially used inconsistently to refer to a variety of forms and functions, including vocal ensembles, mixed vocal/instrumental groups, and the act of accompanying. As the form developed, the term gained its lasting definition. The instrumental concerto emerged in the late 17th century. In Italy, two distinct styles arose, reflecting different approaches to musical structure and scoring.
The Roman concerto featured a small ensemble of instrumentalists (called the concertino) playing in unison, contrapuntally or in alternation, accompanied by the larger concerto grosso or ripieno. Northern Italian concertos were written for much smaller orchestras, with sometimes as little as five instrumental voices, and emphasized the role of a single soloist (usually a violinist) backed by relatively light accompaniment. The genre flourished in the early 18th century with the many innovations of Antonio Vivaldi.
His earliest concertos made use of the ritornello form, in which tonalities are established and reestablished throughout a movement by orchestral refrains. The form was the first to regularly present a recurring musical motif in several contrasting tonalities. Vivaldi also incorporated techniques largely unused outside of opera, such as the orchestral unison and onomatopoeic effects. His compositions contain slow, lyrical passages that allow for and encourage improvisation and embellishment.
Suited to a variety of settings and functions, from secular to recreational, Vivaldi’s concertos were highly accessible and diverse. 2 Bach was among the many influenced by Vivaldi’s style. An unofficial student of the Italian composer, Bach devotedly transcribed Vivaldi’s concertos by hand, often rescoring them.  Bach’s attention to detail and expertise in musical structure gave his own works a refreshing individuality. His compositions included new, virtuosic instrumental techniques and applications, particularly for the harpsichord.
Bach’s Brandenburg Concertos brim with dense compositional textures, complex instrumentations (combining strings, brass, woodwind and keyboard instruments) and unusual mixtures of conventions usually exclusive to their own specific form of concerto. Featuring an astonishing amount of instruments, the Brandenburg Concertos make for a tonally diverse listening experience. Taking every sound in his palette into consideration, Bach orchestrates passages both instrumentally homogenous (specifically, string ensemble) and unusually varied (combining recorder and trumpet).
The instrumental parts are as unique and unusual as they are difficult: violas da gamba back atypically soloing violas, a recorder fights to sing above a trumpet, and a violin piccolo plays a fast melody customarily reserved for other members of its instrumental family.  Following the conventions of the concerto grosso form, the second Brandenburg concerto features two ensembles: the concertino, a small group of soloists, and the ripieno, the larger orchestra accompanying them. The concerto is scored for the violin, viola, flute, trumpet, oboe and continuo.
The elaborate interplay between the soloists and the ripieno is most apparent in the manipulation of recurring musical themes. [pic] mm. 1-7 The first measures establish the ritornello, played in unison by both the soloist and larger orchestra, with contrapuntal voices in the accompaniment. The theme is grandiose; the repeating 16th-16th-8th note motif excitedly calls for the listener’s immediate attention, heralding a rising and falling stream of 16th notes that seems to relay some thrilling news. [pic] mm. 8-9, violin
A second theme, a brief solo, follows the ritornello, marking the entrance of a solo instrument in its every occurrence. The solo instrument is supported only by the continuo and at most one other instrument in the concertino; the orchestra is at rest. The melody floats sweetly, lingering on a trill as a temporary reprieve from the uproar of the orchestra. The second theme is played by the violin in its first instance and in subsequent occurrences by the oboe, flute and trumpet, respectively. The two themes (the first truncated) alternate in rapid two-measure exchanges.
Changes in pitch and direction in the solo passages bring about modulation in the restated ritornellos that follow, shifting the mood of the piece and establishing the soloists and the driving force behind its movement. As the solo guides, the opening of each ritornello serves as a point of arrival.  This pattern is characteristic of Vivaldi’s style: his concertos typically began with a full statement of the orchestral ritornello, which would re-emerge between alternating solo passages in a notably altered form. 3 [pic] mm. 9-11 (top), 13-15 (bottom)
The first example of this occurs in the transition from the solo passage to the restatement of the ritornello in measures 14 to 15. Reflecting a single change in the solo (a high C replaces the F in the last note), the transposed ritornello moves the piece into the key of C, the dominant to the tonic key of F. To the listener, the key change instills a sense of triumphant accumulation and a desire for eventual resolution. [pic] mm. 31-37, trumpet (top) and oboe (bottom) The next modulation takes the piece to the key of D minor, the relative minor to the tonic key.
Against a suddenly (and unexpectedly) downcast orchestra, the high-pitched trumpet introduces a new theme: a simple, prolonged four note sequence that contrasts with the complex and rapid movement of the accompaniment. The oboe answers this sequence between the trumpet’s restatements, gradually guiding it to a lower pitch range. As the trumpet’s sequence tapers off, the full orchestra returns to another restatement of the ritornello.