The simplest method of adding background sound is to include a line like this in your blog template.
<bgsound src="http://yoursite.com/background.mp3" loop=infinite>
Steps to add: Go to Blogger dashboard Design-> Edit HTML-> below body tag add this code.
<bgsound src="http://yoursite.com/yoursound.mp3" loop=infinite>
Example:
<body>
<bgsound src="http://yoursite.com/yoursound.mp3" loop=infinite>
Here http://yoursite.com/yoursound.mp3 is path of mp3file.
