The loud conversation is what the viewer sees from a distance. In this case it would be the white marks on the black expanse. It can be argued that the black expanse - the big square of black - still represents the loud conversation as the painting exists on the light coloured wall. The quiet conversation is the gentle value musings that exist within the dark values and the light values. If the black was a 10 value and if there were dark values (maybe 7, 8, and 9 values) within this 10 value - this would be a quiet conversation. The same goes for the subtle 1, 2 and maybe 3 value additions to the white marks.