I did not say they result in increased noise floor. EVery component has a baseline noise floor. I was describing how the smallest voltage details rise from the thermal noise floor as the voltage division (as the wiper moves or the ladder is varying) result increases. In 99% of preamps on the market the line level signal from the source fisrt meets the passive volume control (potentiometer, TVC, ladder what have you) and then it hits the constant/fixed gain stage (6 dB, 12 dB, 18 dB whatever)
There IS NO GETTING AROUND thermal Johnson noise (that is)physically inherent in every resistor device in the known universe.
There is a sweet spot and it does have everything to do with optimizing the dynamic range and your overall system "sensitivity"
Dave Mitchell: The ARC devices use a digital potentiometer (a plastic case 5 volt IC) that depending on the digital (bit level) value switch in series internal resistors...it is identical in fundamental operation to stepped attenuators. Except in the IC the signal ALSO flows though active devices (multiplexors and buffers). Pick your poison.