Not to be confused with Mitsubishi's ASC (active stability control), in the Lexus RC 200t, is stands for Active Sound Control.
It pretty much let's you controls the amount of synthetic engine-like sounds that come through your interior speakers at high engine speeds. The dial pretty much lets you control how loud you want it, or you can take it off completely.
People have reported that it sounds a bit too digital for their liking though.
Yea.. Can't "fake the funk" with the building dudes ! A lot of companies do this now.. but not all of them allow you to change the volume of it. For example, with Subaru, you have to change a little piece of pipe that they call the noise generator. The pipes have baffling in them and there's different ones with different amounts of baffling.
It works the other way too since some people want all the sportiness but not the sound and overall loud factor that comes in. So even yanking the generator or disabling it entirely could benefit some. Get an interior as quiet as a Buick.