Should i convert to 256 kbps aac on itunes

You'll probably get a slew of 'don't do it because transcoding technically makes you lose quality' posts, but you should be the judge of that. Take one of your favorite and most familiar songs, and do the test yourself.  If you can't hear any amount of quality loss, then do it to the rest of your library to free some space up for your iPod.

I would do it if it was from CD to 256kbps or Loseless to 256kbs.

I don't know about going from 320 to 256 though. 

I'd bet that you'll never listen to 25% of the music on your ipod.  Offload those files and you'll save yourself a lot of trouble, it is a pretty small difference in file size between the two formats.

I thought AAC is recommended over MP3. I have stuff in wma, mp3, lossless, aac, and in a lot of different VBR. I recently put all my music from cd to lossless for my computer, and to 192 aac for my iPhone, and on those aac tracks I noticed a difference right away over mp3 at 192. I think aac in 192 sounds good, especially since you're getting some extra room on your portable device. 

Quote:

Originally Posted by JamesHuntington 

I thought AAC is recommended over MP3. I have stuff in wma, mp3, lossless, aac, and in a lot of different VBR. I recently put all my music from cd to lossless for my computer, and to 192 aac for my iPhone, and on those aac tracks I noticed a difference right away over mp3 at 192. I think aac in 192 sounds good, especially since you're getting some extra room on your portable device. 

HAHA, I'm quoting on myself. Anyhow, I thought I was using 192 AAC on my phone, but I figured out yesterday that I had done 320 AAC on accident. After realizing I had done that I decided to do all my lossless into 256 AAC to see if there was a difference and noticed almost instantly a lacking bass, though it sounds pretty clear. I am planning on going back to 320, which takes up extra space and probably uses more power on your device. I really only notice a huge difference in my car. No amount of EQ-ing makes it as good. My bad, sorry for the bad advice. 

The difference between AAC 256 and AAC 320 wouldn't show up as lacking bass. Odds are the volume is just a bit lower on the 256 files.

Quote:

Originally Posted by bigshot 

The difference between AAC 256 and AAC 320 wouldn't show up as lacking bass. Odds are the volume is just a bit lower on the 256 files.

Yes, maybe volume's lower, especially bass. I'm not a bass head or nothing, but i like to rock. I can't explain why the loss of quality was mostly noticed at the bottom end, but it didn't take long for me to notice. 

Quote:

Originally Posted by bigshot 

I took AAC 256 VBR and copied it to AIFF and back to AAC 256 VBR ten times. The tenth generation transcode sounded excellent. Do a test for yourself. I'm betting it won't make any difference.

This is from MP3 to AAC though. They're different algorithms and I'd imagine it would result in at least some additional quality lost here, since they're picking apart different parts of the data to compress. You'd get the worst of both of them, really.

I'd test myself to see if it does make a significant difference but I can't get the AAC encoder working in dbpoweramp...

Quote:

Originally Posted by bigshot 

The difference between AAC 256 and AAC 320 wouldn't show up as lacking bass. Odds are the volume is just a bit lower on the 256 files.

I've read a comment to this effect more than once, specifically the lowering of volume at different bit rates, it never really sounded logical to me, so...  

Here's what I tried.  Starting with an uncompressed file, I made 3 files, 320Kbps AAC, 256Kbps AAC, and 128Kbps AAC.  Each started with the master uncompressed file, and thus was only one generation removed via AAC compression.

I tested all three resulting files with AudioLeak, all three had exactly the same unweighted and A-weighted volume, to the tenth dB.  The peak levels did change slightly. The master file was at 0dBFS peak, the 256 file was .1dBFS, and the 128K file was at .9dBFS.

So there is no noticeable change in volume from an uncompressed master to one generation removed 128K AAC, and a slight measurable but inaudible change in maximum peak level. 

Maybe different encoding programs? It's much more likely to be a volume difference than an EQ difference.

Quote:

Originally Posted by bigshot 

Maybe different encoding programs? It's much more likely to be a volume difference than an EQ difference.

All my test files were created from within iTunes.

Never said anything about an EQ difference...