Why does the Audio Output sound so bad?

Last week I noticed that a soundfile sounded really poor in Adobe Audition. I assumed it was a bad recording and set about fixing it.

But when I imported the file into Final Cut Pro (or even just played it in QuickTime), I realised that the problem wasn't the file, but Adobe Audition. I have since seen similar descrepancies with other audio files and other apps e.g. Logic Pro. All the soundfiles sound terrible in Audition (like a 70s transistor radio) but fine in other apps.

I can't find any answer to this - hence I'm posting it here. I don't know if this is the issue, but under preferences > Audio Hardware, the Sample Rate is 8000 - and it won't let me change this.