How to convert .at3 files to .mp3 format?
Converting Sony ATRAC3 Audio Files directly to MP3 Audio Files (.at3 to .mp3 conversion) is possible and should be quite straightforward.
Use an audio editing software or (online) conversion tool, such as Sound Forge Pro or Sony SonicStage, which should allow users to import AT3 audio files and export them in MP3 format.
A dedicated audio production program
Audio data management program for portable devices
A digital audio editing software
Video, Audio & Streaming for creators.