Jazz improvisation is the process of spontaneously creating fresh melodies over the continuously repeating cycle of chord changes of a tune. The improviser may depend on the contours of the original tune, or solely on the possibilities of the chords' harmonies. It has been said that the best improvised music sounds composed, and that the best composed music sounds improvised. Composed music and improvised music may seem to be opposites, but in Jazz they merge in a unique mixture. The challenge to Jazz improvisation is playing music with both spontaneous creativity & intentional conviction.