BBC's Graham Satchell singing
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How much musical auto-tuning is acceptable on TV?

Millions of viewers settled down on Saturday night to watch the return of the X Factor, but for some the singers did not sound natural. That sparked a debate about 'auto-tuning', which is often used in recording studios to change vocals.

The programme insists it only altered pre-recorded items and not live performances but the debate will not go away.

So what is auto-tuning?

BBC reporter Graham Satchell has been finding out.

Go to next video: X Factor admits to vocal tweaks