Ever since the advent of the LP in the 1950s with its expanded capacity, the six Brandenburg Concertos have been Bach’s runaway hit. They were not written as a set but form a collection. Nos. 4 and 5 are the brightest, the most buoyantly happy and the danciest, but in some ways they are also the most complex. By putting these concertos under the musical microscope we can discover how their many ingredients combine to make two of the most irresistible works in the repertoire.