Roger Ebert was able to recapture his voice thanks to a unique technology pioneered by a company named CereProc. Ebert's initial attempts to capture his voice electronically led to a sound that was too electronic and without personality. CereProc, however, was able to successfully create a digital voice that sounded like Ebert using only audio recordings from DVD commentaries he made.
CNET has a fascinating interview with the company's Chief Voice Engineer in which he elaborates on how they accomplished this:
Q: Chris, how do you actually create someone's voice using your technology?
Pidcock: When we build a voice for ourselves, we have a special script that covers lots of the sounds of English. It's quite rich and detailed. We get people into a studio and spend 15 hours or so recording them. But afterwards, the voice creation process can be performed on audio and text from anywhere. That's how the Roger Ebert project came about. He got in touch with us because he saw our little George Bush talking head. That was a good example because obviously we couldn't get [Bush] to sit in our recording studio for 15 hours. So we used his weekly radio address, which had both the text and audio on the White House Web site. We downloaded it and put it together, and out came the synthetic George Bush.
We take that audio data and send it off for transcription and then segment it into very small pieces. The technique is similar to the one used by AT&T's NaturalVoices of selecting different pieces, or phonemes, of the audio and stitching them back together in clever ways. The trick is stitching them back together so they don't sound like they came from different context and different words. And obviously now Roger can say anything he likes--he's not restricted to the words he used in his DVD commentaries.
Be sure to read the whole thing here.
Watch Ebert debut his new electronic voice on "Oprah" below.