Word for a casual performance (example: Bowie performing Heroes live in Berlin 2002)

understated
_ADJECTIVE

presented or expressed in a subtle and effective way

‘understated elegance’

_{Source: Lexico}

Compared to his famously glam rock performances, this is a stripped down performance.

Drop Everything And Watch Taylor Swift's Stripped-Down Performance Of "Wildest Dreams"

https://youtu.be/OGDkg3QiJmk

It tends to refer to both the subdued musical arrangements and the performance together.

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