X Factor fans' chorus of disapproval over digital improvements

X Factor bosses faced an angry backlash from fans today after admitting digitally tweaking contestants' vocals.

Viewers have flooded internet message boards and Twitter claiming the show used Auto-Tune — a technology that corrects pitch and disguises off-key mistakes. Its use can be spotted because it gives the singer a slightly robotic sound.

An X Factor spokesman admitted that post-production work was carried out on vocals, but that the judges had made their decisions based on unchanged live vocals.

The move was criticised by leading vocal coach Carrie Grant, who felt it cheated viewers. She said: "I was thinking, Why would they put that on someone's voice when the public are meant to see them in the raw?' Surely the idea is to see them improve?"

Fans tweeted their disgust, with Rina Sawayama saying: "Just when I thought reality TV couldn't get more unrealistic."

The X Factor spokesman said: "The judges make their decisions at the auditions stage based on what they hear on the day The footage and sound is then edited and dubbed into a finished programme, to deliver the most entertaining experience possible for viewers. When it gets to the live shows, it will be all live."

Viewing figures for Saturday night's new series reached 12.6 million. Among the potential stars was Gamu Nhengu, an 18-year-old student who wowed the judges with her version of Katrina and the Waves' Walking On Sunshine.