Unless you have definite reasons for doing this - such as that you are a musician and the people coming to your site will expect to hear a clip of your music, you should avoid adding music that plays automatically if at all possible.
Music that plays automatically is one of the quickest ways to get people to leave your site, either because they need it to be quiet because they are browsing the internet in an office, computer lab, library or because it clashes with their own music that they are playing on their computer.
Most people react by closing the browser tab or window the second the music starts to get rid of the unwanted intrusion as fast as possible. However, if you still decide that background music is appropriate for your site, you can find more information on this link.
You may also be interested in this article, it gives very sound advice on the implications of adding music to your website. Please review it carefully before you proceed: Background music.