Behind the scenes at Pitch Battle
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Pitch Battle: Behind the scenes with Gareth Malone, Kelis and Chaka Khan

Thirty choirs are battling it out in new BBC Saturday night singing contest Pitch Battle.

The BBC's Colin Paterson goes backstage to meet some of them, along with host Mel Giedroyc, judges Gareth Malone and Kelis and one of the series' guest judges, Chaka Khan.