Thank you so much Stephen! to be more precise: some users at
http://www.audiostory.com/ would like to convert a 10MB MP3 into a 5MB MP3 (for example) so that they can have all their favourite audios in their old low capacity MP3 devices. I've tried myself several audio editing softwares but Im not convinced which one I should advise as they all seem to reduce the quality..
Thank you for your assistance!