Iterative looped acapella performance

This is a performance art concept. It would be a familiar song; maybe a christmas song. The performer starts by humming at the microphone. After a minute of this you hear her humming start again as the first time is played back. Accompanied by the recording of herself, she now makes different sounds. The third iteration contains the first and second, and so on. Then backing vocals. Eventually she gets to the lyrics and sings them, adding harmonic parts and countermelody as the whole song builds up. Trick 1 is that even though it is looped it is also mixed; not all parts remain at the same stage volume she sang them. Trick 2 is that the microphone is tightly directional and records only the live vocals, not recording the previous ones as they are played again together.

The song seems done but at the end the whole thing she has just made is played again. She sings a different song in a different key over the top of it - maybe a Beatles song? - and it matches.

I can imagine this so clearly I wonder if I have seen it done.