I've noticed that there are two dials below the handwheel on the GHG compensator.
What was their use? Could the high pass filter be adjusted with them?
As far as I understand the higher the frequency, the better the accuracy, but also range gets worse. I believe that such adjustments had to be possible as with fixed filter one wouldn't hear the higher frequencies without a proper amplification.
My leading theory is that one of these knobs adjusts the cutout frequency, while the second one adjusts the volume gain, but I haven't found any sources that would confirm that.
Any help in figuring this out will be greatly appreciated!