Quote Originally Posted by Sjoasja View Post
осеннее as-sen-n'i-ji
осенние as-sen-n'i-ji

осеннии as-sen-ni-i

осенняя as-sen-n'uh-juh
я
This is how i imagine saying it. -ие -ее the same, whereas the -ии wouldn't have the Y-sound for the last vowel. And the -яя would be the schwa sound of fathEr, with the last vowel a Y-sound to it.
осеннее, осенние and осеннии all are [ɐsʲenʲ:ɪ.ɪ] for me. (Reduced a, soft s, stressed e, soft long n, short i and short i again)
The difference can appear only when I pronounce them slowly, sound by sound.

осенняя is [ɐsʲenʲ:ɪjə], with the first я reduced to [ɪ]. But [ɐsʲenʲ:əjə] sounds good as well.