I can't tell the difference between some sounds.
ودي vs ودّي
بَسّام vs بَسام
Whenever Duolingo shows me a sound for Widii / Widdii (or Basaam vs Bassaam) they sound the same. I know the Shadda is supposed to make the consonant longer but it does not appear to be so for those two sounds.
For other sounds I can hear the distinction between the lengths but am I missing something?
Just keep in mind that depending on the exercise the audio is very likely being produced with a speech production softwares, and they aren't perfect. So if you hear something that doesn't sound like you expect, it doesn't mean you are understanding it incorrectly, it can also mean that there is a flaw in the audio. The shadda will always indicate a double consonant, whether or not this is reflected in the audio.