Signal to noise ratio. If your noise is at some average amplitude X, and you have signal at two levels, Y and Z (and both average above X, because otherwise you

Signal to noise ratio. If your noise is at some average amplitude X, and you have signal at two levels, Y and Z (and both average above X, because otherwise you would just perceive X distorted a bit), then the lower of Y and Z will have more of its amplitude within the average X amplitude. I.e., if Y < Z, Y/X < Z/X, then (loosely), Z will have a larger percentage of its signal that is not masked by noise.