I was listening to a friend's 4th gen with the stock apple headphones and then loaded the same song onto my ipod and both with apple phones and the shure e3's the sound was noticably more vibrant on the 4th gen. All songs sounded more lifelike than I have ever heard on mineI dont know much about the software on my ipod, but I know my boyfriend loaded the most recent version as of 6 mos ago onto my ipod. For what its worth both are 20GB models.