im using lc-aac (low complexity) at cbr 448kbs or vbr 450kbs the main difference is 320kbs mp3 go upto 16khz where as 448kbs go to at least 20khz the same as cd. im goin to try recording off vinyl to see how high it can go as iv got records that go upto 45khz no matter what they say you can hear the difference in 4khz its just people would rather put 13,000 mp3s at 32kbs on a play as sony says you can put that many tracks on than put 4,000 good sounding 320kbs mp3s or mp4s its like people dont care what music sounds like nowadays aslong as its an artist they like phones for example worst sounding tweeters iv ever hear with full range being played though them to make them sound worse hence why i got a nw-a3000 its rated as the best sounding out of the portable player range