In contrast to compression, which decreases the level of a signal after it rises above the compression threshold, downward expansion decreases the level of a signal after the signal goes below the expansion threshold. The amount of level reduction is determined by the expansion ratio. This type of expansion reduces the level of a signal when the signal falls below a set threshold level. This is most common used for noise reduction. For more information on Downward Expansion and Dynamics Processing, please refer to this article.