Earlier quoted context omitted.
"At least at the lecture I attended, he live keyed his entire speech. This meant the synthesizer would speak, followed by 20 or 30 seconds of absolute silence as he buffered the next few sentences." He was "typing" one bit at a time? How can he type the entire sentence so quickly?
Yes. Here's some info on his setup. It tracked the motion of his cheek, which he could still control, to stop on a letter. It scanned through the alphabet and he had to pull it up at the right time. http://www.hawking.org.uk/the-computer.html I also just started typing that in present tense ('tracks'...) and had to pull myself up. :(
This would have been circa-2004, and I want to say at the time he had a less predictive but more physical system.