What is TTS?
Where is the welcome-thread? I'd like to see what it says about "De". My boyfriend is from Sweden and he says there is no such word or it might be slang. He also says the speaker has a Stockholm accent. I would have preferred a speaker with a neutral way of speaking, like in the US the way national news anchors have no regional accent.
Yes, the Swedish O can be either /ʊ/ ("hook") or /u:/ ("boot"), or /ɔ/ ("not") or /o:/ ("yawn") This is due to a vowel change hundreds of years ago. It's not a matter of long vs short, since it can appear in any of the forms. Generally, it takes a /ʊ/ sound (short "oo") at the beginning and end of words, and an /ɔ/ or /o:/ sound otherwise. Also, stressed open syllables on -o are usually /u:/. But that only a very broad generalization, and you'll have to learn which ones are which way.