Trumpeters in Bach's time alternated between instruments with a variety of ranges when performing
Trumpets have had valves similar to the ones used today since the middle of the 19th century. In the 17th century the "natural trumpet," which is limited to the notes of the natural harmonic series, was most common. For that reason, the musical scales that could be played were very limited, and in contrast to the modern trumpet the chromatic scale could not be played. Accordingly, trumpeters of the time switched skillfully between a number of trumpets in different keys during performances.