That's an aural range approach. If you flew them accurately you got a steady tone in the headset, drifting into the “A” quadrant resulted in hearing that, same for the “N”. It was only the A amd N overlapping that gave you the steady tone. That was called riding the beam. Over the station was the cone of silence, which entered into the popular culture and that’s where the idea came from on those old “Get Smart” shows.
We used to train in war surplus Link trainers that had those approaches and of course thought ourselves just average if we could fly them. ILS on the other hand was more tricky which says a lot about the quality of simulation in the Pleistocene era.