In the WTFuture Eddisode the future Edd , Tom and Matt their voices are actualy their normal voices but the voices are pitched down with Audacity, As seen in the behind the scenes video on Matt's channel , you can see it on the computer in a short period of time. the video : . This is the same video where Edd gets all cold and has to change because Tom pouring cold water all over him for the "son of a blublbubl its delicious' part.