FastrSlowrPlayr is a javascript widget which allows you to embed a mp3 file and control it's playback via javascript. It provides you with easy access to the various things you may want to do to the mp3 (e.g. playing, stopping, changing the volume etc) and it also allows you to change the playback speed (and therefore pitch) of the playing mp3.
The simple example on this page shows how you can embed an mp3 in a page which automatically loads and plays. The swf which powers the mp3 playback is included in the div with an id of playerHolder (below) although it has no visual component so there is nothing to see there...
This page uses console.log to give debugging messages and tries to do various things to the loaded mp3 file to test different pieces of FastrSlowrPlayr's functionality. So view it in Firefox with Firebug or another browser that supports console.log. If console.log doesn't exist then the messages are basically ignored but I ensure that it doesn't break the page (so you can still test it in e.g. IE). View source to see what's going on!
If this plugin is too low level for you and you would like a user interface for your mp3 playback device then please have a look at FastrSlowrPlayrUI.