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.
The AVR file extension is a data format known as Audio Visual Research File. AVR files were developed for use on Apple Macintosh computers. They were specifically, used for the older 680x0-based Atari ST computer systems.