atp to mp3 conversion is most probably a case of audio export/transcoding between Sony Music format (.atp) and standard MP3 files. It would be hard to find a tool that can export to MP3 audio, the real problem will be in finding some tool that can work with Sony's ATP format. It's format that has been used in consumer electronics over decade ago, so perhaps you might reach out to some of the old audio tools as well.
Updated: August 15, 2023