Slowing down the playback of an audio file without changing its pitch?

Question

I am working on an application for college music majors. A feature i am considering is slowing down music playback without changing its pitch. I have seen this done in comme

Answer 1

This site explains how it's done in the physical world: http://www.wendycarlos.com/other/Eltro-1967/index.html

I don't know how you would emulate that in software though... I'll keep looking