Johann Sebastian Bach is a composer that falls into the Baroque era (late Baroque era to be precise), but he did compose some works in the new gallant style, for example the Six Sonatas For Violin And Harpsichord. That Bach was a master of the so-called old style is true, but he was far more than that. He was a culmination of the late Baroque, and within that culmination were the seeds of the newer style, a style he was well aware of and more than capable of composing in.
While Bach is not thought of as being an innovator, he was quite creative in every facet of music and composition. The art of instrumentation for many years was thought to have been quite primitive in Bach's time, but the opposite has been found to be the case. With a wide variety of instruments and timbres, the Baroque composers and Bach in particular took every advantage of the differences in musical instruments to create tonal color, nuance and expression. One of Bach's many experiments in instrumentation is the Brandenburg Concerto No. 6 In B-flat. The concerto is scored for two violas, two violas da gamba (already considered an old instrument when this concerto was written in 1721), one cello, one violone (bass fiddle) and harpsichord. No soprano instruments save for the upper register of the keyboard. The resulting tonal color in the hands of a lesser composer would perhaps have become too dull and monotonous, but Bach writes music of great beauty in a joyful bluish purple color. The concerto is in three movements:
I. No tempo designation - Usually played in allegro tempo, this music has the two violas playfully chasing each other in canon interspersed with dialogue for the other instruments. While the violas chase each other the accompaniment of short repeated notes give a sense of movement to the music while the alternating sections go through key changes that add interest. Bach was said to have enjoyed playing the viola, so perhaps he took special delight in this movement. The violas da gamba play an accompaniment throughout and add movement and color to the overall tone of the movement.
II. Adagio ma non tanto - The violas da gamba are silent in this movement as the violas play a melancholy aria in duet. The cello and continuo alternate accompanying and playing sections of the aria. The movement ends with a whole note chord that gives a sense of suspended movement.
III. Allegro - In the style of a gigue, the violas begin in unison and soon chase each other even faster than in the first movement. The violas da gamba add to the texture and tone color while the cello has a few things to say of its own. The music for violas keeps moving in alternate moderate and fast note values until it reaches a point when the beginning section of the movement is repeated until a full close is reached.