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.
AAC is an audio file format that works similar to MP3 but compresses more than MP3. It significantly reduces the audio file size without losing the quality. To reduce the file size it uses the MPEG-4 standard to cut off the low frequency sounds that cannot be heard in a human’s ear.