It is a chord accompaniment throughout the piece. Once the figured bass was a common form to place on top of music, it was easier to play music without certain notes, and this is somewhat how baroque improvisation was born. It is even said that Bach improvised many of his pieces on the piano and in his head and then wrote them down. In this way, much of today's Baroque music can be considered improvisation. There was also a stable base form (continuous basso and step base) for both types. Miles Davis is also said to have written several improvised solos. He would have heard people playing melodies and created a new melody from these melodies.