compander
(kəmˈpændə) n (Broadcasting) a system for improving the signal-to-noise ratio of a signal at a transmitter or recorder by first compressing the volume range of the signal and then restoring it to its original amplitude level at the receiving or reproducing apparatus
[C20: from com(pressor) + (ex)pander]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014