attenuation, fading -- (weakening in force or intensity; "attenuation in the volume of the sound")
Overview of verb fade
The verb fade has 4 senses
fade, melt -- (become less clearly visible or distinguishable; disappear gradually or seemingly; "The scene begins to fade"; "The tree trunks are melting into the forest at dusk")
fade, wither -- (lose freshness, vigor, or vitality; "Her bloom was fading")