Complex sentence: Swing improvisers commonly emphasized the first and third beats of a measure, but in a bebop composition such as Dizzy Gillespie's "Salt Peanuts", the rhythmic emphasis switches to the second and fourth beats of the measure.
Split into simpler sentences: Swing improvisers commonly emphasized the first and third beats of a measure. But in a bebop composition such as Dizzy Gillespie's "Salt Peanuts", the rhythmic emphasis switches to the second and fourth beats of the measure.