How do you fire jabs really fast?

ken, ryu, guile, vega, m bison, chun li, etc. they shoot jabs really really fast. how do players do this?

http://forums.shoryuken.com/discussion/119352?threads/mashing-and-button-pressing-in-st.119352/

Essentially it’s just using really good timing. Personally I use the double tap method, but you can’t go too fast.