What does a dedicated audio chip actually do to music?

Most music designed mobile phones like Nokia's xpressmusic and Sony's walkman series come with a dedicated audio chip to enhance the audio sound quality even more further.Both the Nokia x6 and 5800 have this chip and you can tell the difference from a phone that has no chip.The idea of having a audio chip in your music player is you get crystal clear and distortion free sound.A audio chip is specially designed to produce a better output signal by processing the sound in more of a depth, but to tell the sound quality difference from a dedicated chip you have to listen to high quality music files and use a decent set of buds.