The effects of helium and sulfur hexafluoride gas

If you have a helium balloon you must not miss the chance to completely transform the timbre of your voice! 

In fact, since this gas is lighter than air it "facilitates" the vibration of the vocal cords at a higher frequency, which results in a higher vocal timbre. 

However, you might ask, is there is a gas that produces exactly the opposite effect? That is to say, a voice that sounds very powerful and almost demonic?

Absolutely, and it is called sulfur hexafluoride! Look what happens when you inhale it ...