I have been ripping all my music 320 AAC for my iPod. As my disc is filling up, I decided to look at little more seriously into some better compression. From most of my looking around, I found that the EAC/LAME --alt-preset extreme would be my best bet for what I was looking for.
After ripping a number of albums and listening to only a few of them, I found that most of the time differences were minimal if existent (using 30 GB iPod photo and Sennheiser PX-100s). However some albums seem better at 320 AAC...significantly so. I am curious as to other's finds. I am not sure if the levels are equal on each rip, but the difference almost sounds like the difference between CD and vinyl (a weird comparison considering we are talking compressed digital). The 320 AAC sound more lush...and fuller. My question really is...am I hearing voume differences and equating that with fullness, or is there distinct difference between these two file types. Obviously there is in size, but I am more interested in the bottom line between the two. If the same sonic transparency essentially exists between the two of them, but the levels are different...all the adjustment would need to be would be raising the volume. However, if the levels are equal...then I have answered my own question. Unfortunately, I can't tell that.
There is another possible explanation, that is very likely:
You are imagining it.
Did you do a blind comparison between the two?
Checking volume could be done by decoding the two and running wavegain on them.