"sound quality is not that good"
Hmm, doesnt really tell us much mate. it could be that your system resouces are heavily loaded. I have noticed when i play MP3s, cds, DVDs or other files containing audio formats that sound may become jittery &/or digitized, particularly if certain other resouces are needed for the sound file are you playing. What sort of sound file? and where is it being played from? may help in solving your problem?