Sound on PowerPoint across slides?

There is an article ,maybe ia what you want.Please check ie out below:

How to Add Music Song to PowerPoint Presentation

http://www.ppt-to-dvd.com/learningcenter/how-to-add-music-song-to-powerpoint-presentations.html

read this article:

How to Play a Sound across Multiple Slides in PowerPoint

To make a sound continue through multiple or all slides, follow these steps:

1. Go to the slide where you want to begin your audio track (defaulted as the first slide), and select Insert -> Movies and Sounds -> Sound from File to insert the sound.
2. After you click OK, you can see a message pop up asking how you want the sound to start in slide shows. Click Automatically.
3. Select Slide Show ->Custom Animation to enter the Custom Animation pane. Your soundtrack is listed below in the pane.
4. In the drop-down list of the sound, choose Effect Options. Then the Play Sound interface appears. In the Effect tab, click the radio button beside Stop Playing After XXX slides (which indicates how many slides you want this song to play across) to enter the number of slides you intend to add. For example, you can enter a number from 1 to 999 for this field. Then the sound will play throughout the specified slides.

5. Next, check the settings in the Timing tab. To play automatically, you can set to Start After Previous with a 0-second delay. Click OK to exit the dialog box.
6. Then go to Sound Settings tab, adjust the sound volume as you like. You can also tick to hide sound icon during slideshow if you don't want it appear.

Now you can play the soundtrack from the very beginning to the end of your slideshow.

In order to add sound or music to a PowerPoint Presentation follow these steps:

1. Display the slide to which you want to add music or sound effects.

2. On the Insert menu, point to Movies and Sounds, and then do as following:

Click Sound from File, locate the folder that contains the file that you want, and then double-click the file.

3. Double-click the sound file that you want to insert.

4. When a message is displayed, do one of the following:To play the music or sound automatically when you go to the slide, click "Automatically".To play the music or sound only when you click the sound icon, click "When Clicked"

After these step, your music is added to PowerPoint presentation.http://www.powerpoint-resources.com/powerpoint-questions/how-can-you-put-music-in-powerpoint.htm