MPEG-1 Audio Layer III (MP3) applies psychoacoustic lossy compression to remove frequencies the human ear perceives least, producing small files at acceptable audio quality. AU file (AU) stores data in the AU format. This conversion changes the file's encoding, compression method, and supported feature set. Metadata such as creation date and embedded colour profiles is preserved where the target format supports it. The result is a standard AU file readable by any compatible application. 1converter handles MP3-to-AU conversion server-side: files are uploaded over HTTPS, processed on isolated cloud infrastructure, and the converted output is available for download for 24 hours before automatic deletion. No account is required for standard conversions.