The timing in jazz ensemble performances was investigated in order to approach the question of what makes the music "swing." One well-known aspect of swing is that consecutive eighth notes are performed as longshort patterns. The exact duration ratio (the swing ratio) of the longshort pattern has been largely unknown. In this study, the swing ratio produced by drummers on the ride cymbal was measured. Three wellknown jazz recordings and a play-along record were used. A substantial and gradual variation of the drummers' swing ratio with respect to tempo was observed. At slow tempi, the swing ratio was as high as 3.5:1, whereas at fast tempi it reached 1:1. The often-mentioned "triple-feel," that is, a ratio of 2:1, was present only at a certain tempo. The absolute duration of the short note in the long-short pattern was constant at about 100 ms for medium to fast tempi, suggesting a practical limit on tone duration that may be due to perceptual factors. Another aspect of swing is the soloist's timing in relation to the accompaniment. For example, a soloist can be characterized as playing "behind the beat." In the second part, the swing ratio of the soloist and its relation to the cymbal accompaniment was measured from the same recordings. In slow tempi, the soloists were mostly playing their downbeats after the cymbal but were synchronized with the cymbal at the off-beats. This implied that the swing ratio of the soloist was considerably smaller than the cymbal accompaniment in slow tempi. It may give an impression of "playing behind" but at the same time keep the synchrony with the accompaniment at the off-beat positions. Finally, the possibilities of using computer tools in jazz pedagogy are discussed.