mono/MonoGame — pull request #2736 by Nezz (2014-06-23 16:08:21+00:00)
Title: Fixed music volume on WP8

Unlike other volume implementations, MediaElement uses a linear scale. This means that if you set the volume to 50%, it will not be half as loud, but it will be almost totally silent instead. The approximation of using the 4th root seems to work well.

See discussion for further details:
http://community.monogame.net/t/wp8-music-volume/178