A technical note to myself here, but may help others as well. When I imported .mp3 files from my Olympus Digital Voice recorder WS-831 to my PC it was no longer possible to play the files. The solution is to go to Windows Explorer and change the extension of the file from filename.MP3 (MP in capitals) to filename.mp3 (mp in small letters). Then they should play on the PC. They can also then be imported into other applications (e.g. audacity) without any problems.