CVU file is a CVSD Unfiltered Audio. Continuously Variable Slope Delta modulation (unfiltered) is an alternative handler for CVSD that is unfiltered but can be used with any bit-rate.
AC3 is an audio file format that uses Audio Codec 3. Dolby Digital developed AC3 that gives a surround sound experience. It is mostly used in DVD or Blue-Ray disks. It supports 6 Channels music and can provide 6 different sound effects. This lossy format effectively encodes the surround sound system.