Ujjayi is an audible breath and has been likened to ocean waves, breathing through scuba gear, or Darth Vader’s famous inhalations/exhalations. While the sound produced during ujjayi is significant and often noted, it is not the defining characteristic. For instance, free breathing with noise is not ujjayi, even though it is sometimes referred to this way.
According to some yogis, ujjayi and asanas should not be practiced at the same time; some even say ujjayi is simply not possible to perform properly during difficult asanas due to the length of the breath. Others believe it will occur naturally during an asana when a yogi masters the pose. In vinyasa yoga, however, ujjayi is considered an important technique for synchronizing the breath with movement, and is thus used frequently.