You'll have to use the 'obsolete' frameset tags (to me they're the best), put your songfile in those unchanging pages and you should have no problem. A webpage doesn't need to be visible, it may just contain your song file.
A Frameset divides the page into panels, each panel populated by a webpage. When a link is clicked in a panel, it only changes the panel you are clicking on (it is possible to alter that behavior).
Therefore you should have two panels ("frames"): one for your songfile, another one for you asp.net development.
Create a new html file and use the following code (name it index.html or something):
<html>
<head>
<title>This is the actual title people will see</title>
</head>
<frameset rows="0,*">
<frame src="song_page.html">
<frame src="My_ASP_Start_Page.aspx">
</frameset>
</html>
This page must become your start page in the project. Notice there is no body tag.
The song_page.html should contain your song.
The upper panel populated by song_page.html will not change when users interact with the site, because your site is in the lower panel. Hence, the song file should never interrupt cause it is not in the same frame.