I've been using Express Scribe for about a year now and have recently upgraded to the paid Pro version.
However, I have some ongoing issues with some sound files that are still not resolved in the Pro version:
1. DS2 files - some files will play quite happily for a few minutes, then the sound cuts out. Yet when I play them on another piece of transcription software they're fine. (I prefer to use ES as I find it easier to work with than the alternative I have for DS2 files!).
2. DSS files - I have one client in particular who sends me batches of DSS files and, more often that not, t