Step 1 : Introduction to the question "Which 1940s style incorporated fast notes and emphasis on improvisation?"
...Also called “bebop” in onomatopoeic reference to the sound of a common musical phrase in the genre, this style took over the scene around the mid-20th century thanks to pioneers like trumpeter Dizzy Gillespie. This new sound was an important development in jazz, marking the end of the old, big band swing music style and the start of a new style that was more fluid, rhythmic, and riff-based.