You should do this in sound editing software. The volume setting in PPT only
works for sounds generated by your computer. (So I believe that means it
should work for MIDI, but it doesn't always seem to.) This is one of the
most poorly labeled settings in PPT, and there are quite a few on that list!

Signature
Echo S [MS PPT MVP] http://www.echosvoice.com
What's new in PowerPoint 2007? http://www.echosvoice.com/2007.htm
Fixing PowerPoint Annoyances
http://www.oreilly.com/catalog/powerpointannoy/index.html
PPTLive! Oct 28-31, New Orleans http://www.pptlive.com
>I am trying to put a low volume song in my show that will play continuously
>till it finishes.
[quoted text clipped - 5 lines]
> Any ideas please?
> Oh........ the music is a MIDI & the voice is a WAV.