Not many pop stars produce their own vocals. Ari is special as we all know ❤️for a lot of this album she made it at home by herself she said. Like when she sings my hair and does the chorus in whistle tone she said she had just gotten out of the shower and sounded good so recorded it real quick lol!!
We can't hear her through the glass, but through the speakers the producers use. They're not wearing headphones in this session. As you can see on 5:39, we hear her getting louder as she gets closer to the mic.