Let's say your computer emits a inaudible signal at 4.127Hz when the A key is pressed, 4.131Hz when the B key is pressed, etc. There is a unique signal emitted

Let's say your computer emits a inaudible signal at 4.127Hz when the A key is pressed, 4.131Hz when the B key is pressed, etc. There is a unique signal emitted for each key. It sounds like they just modified the driver to make those signals easier to detect. (i.e. A became 4Hz, B became 4.1Hz, etc.) If they had more sensitive detectors, maybe they wouldn't need to modify the driver. My guess.