Behind the scenes at The Big Sing 2015

The massed choir during the 2015 finale. Photo RNZ/David McCaw.

The Gala Concert is about to start. Photo RNZ/Rebecca Blundell.

All 700 singers rehearsing the massed choir item for tonight's Gala Concert. Photo RNZ/Rebecca Blundell.

Choirs gather on stage. Photo RNZ/Rebecca Blundell.

Burnside Senior Chorale getting ready to go on stage. Photo RNZ/Rebecca Blundell.

Planning a Mexican wave? Photo RNZ/Rebecca Blundell.

Rehearsing on stage at the Michael Fowler Centre. Photo RNZ/Rebecca Blundell.

Big Sing 2015 participants gather. Photo RNZ/Rebecca Blundell.

Students from a Christ's College and St Margaret's College combined choir called Collegium being interviewed. Photo RNZ/Rebecca Blundell.

Radio New Zealand's sound mixing desk at The Big Sing 2015. Photo RNZ/Rebecca Blundell.

Radio NZ Sound engineer Steve Burrage preparing at the Michael Fowler Centre. Photo RNZ/Rebecca Blundell.

Radio New Zealand's sound mixing desk at The Big Sing 2015. Photo RNZ/Rebecca Blundell.

Step inside... Radio New Zealand Concert at The Big Sing. Photo RNZ/Rebecca Blundell.

The calm before the storm... Photo RNZ/Rebecca Blundell.