UHQ upscaler- explanation?

What does this setting (found under equalizer) do? By default (at least on my android device) there is audible noise and distortion that is noticeable on quiet passages of certain tracks. Turning "bit upscaling" on removes the noise. So far so good. Turning on "bit and bandwidth upscaling" seems to change the frequency response of the sound, emphasizing low frequencies. These changes are quite obvious and measurable.

I would like a technical explanation of what these settings are doing. Theoretically bit upscaling shouldn't do anything unless the 44.1 khz -> 48 khz resampling is extremely poorly implemented by default. And bandwidth upscaling (which I'm assuming is just upsampling) should not have any audible effect, let alone change the frequency response.

I am interested in transparent, uncolored audio playback. Yet these settings make me question if I'm getting that. Can anyone explain?