In this scene, Jedda (Rosalie Kunoth-Monks) sits and begins to play the piano in a European style. This music is directly associated with the actions occurring on screen (that is to say, diegetic music).
But as she continues to play the instrument, we begin to hear Aboriginal music (including clap sticks, didgeridoo and singing), which has no clear synchronisation or diegetic source (although the film makes a visual association with the Aboriginal implements hanging on the wall in front of Jedda).
The two forms of music (European piano music and Aboriginal music) begin to interfere with each other in her mind. The clash of the music emphasises Jedda’s torment and split identity, which is suggested when she becomes overwhelmed, stops playing and bangs her head on the piano.
This is yet another example of the efficiency and power of music in its ability to convey crucial narrative information.