MP3 to acc

No. Both mp3 and AAC compress sounds in part by tossing out some data considered non-essential. This happens every time you compress, even if you use higher quality settings. It is like making a photocopy of a photocopy. So converting a 128k mp3 to 256 AAC will probably end up with a file that sounds like 99% of the original 128k mp3. It won't upgrade the sound and it will even make it slightly worse. It won't sound terrible and you might not even notice the difference but it won't be as good. If you need an AAC you are better off changing the rip settings from the original source.

I'll add that converting a 256k mp3 to a 256 AAC will probably end up with a file that sounds like 99.5% of the quality of the original mp3.

As always when posting here it helps to include some context. Sometimes this kind of question is like somebody coming into a room holding a nail and asking where they can find a screwdriver.

Hi,

If it is your aim to upgrade lower quality tracks, you could consider iTunes Match Subscribe to iTunes Match - Apple Support

Jim