It helps to practice listening to voice without reading
I have been having a little problem understanding the French pronunciation, as some of the words seemed to sound similar. I started wondering if the computer is pronouncing it weird. In fact it is not weird for the most part (obviously, I need more practice). I decided to practice just listening to the voice without looking at the screen. It is already helping me quite a bit. I am playing a game of closing my eyes before I move to the next question and I am trying to guess what's on the screen. It is fun and I am making progress on understanding the pronunciation :)
I've just started doing this too and noticed a difference immediately! But if anyone else has tips on how to improve their hearing of the pronunciation, I would be interested because I'm finding it difficult also :)
What really helped me was to read along a book while listening to its audio book version. I started with Harry Potter which was quite good for that. You could also watch movies in French with French subtitles although I find it very irritating that they often don't match exactly. There are several audio books for beginners that come with a written version of the story, so you can read along easily.
And finalement, there is "le journal en francais facile" de Radio France Internationale, which always comes with a transcript, so you can listen to the journal while reading: http://www.rfi.fr/lffr/statiques/accueil_apprendre.asp
Also try using Memrise (I use a couple of popular and free french programs on it). It is basically a pure vocabulary list with brilliant audio. When using it I always take the time to repeat, several times, the words, and I find it significantly increases my own pronunciation as well as recall abilities.
I think the audio is the one big gap in the Duolingo method (otherwise I love it).
The pimsleur method says the exact same thing. It likes learners to just listen and repeat. I think this is the biggest gap in the duolingo method is that it does not promote the sounds (I think only half the questions use sound).
I have subscribed to a trial of "slow news in french" which is a weekly newsprogram spoken slowly, and complete with audio transcripts and grammar lessons. http://www.newsinslowfrench.com/
http://www.fsi-language-courses.org/Content.php This site is really boring and tedious but the 6 month free courses are the same ones that the government agents used to learn various languages. After 6 months very day you are meant to be able to talk fluent from the comments i have read. but apparently you sound very formal (no slang not much informal practise). They go in depth repetition on listening and speaking repetitive phonetic breakdown of vowels and nasal sounds. It's all free and awesome! We live in a world of free education which is very lucky
Many times a tiny little difference in pronunciation changes the word completely (form singular to plural, masculine to feminine, and so on). But unlike English, French Phonetics is quite predictable, and once you understand how it works and put some effort into learning it, it gets incredibly easy to speak, write and understand correctly. It could take years to get to a good level of accuracy in listening and pronunciation if you're only watching movies or listening to podcasts. My suggestion is to tackle this problem right from the start. I'm using the FSI Introduction to French Phonology, which is free on the internet, and it is helping me immensely. I should say that for some people FSI can be incredibly boring, but in my opinion it is well worth the effort.