The full range spans 320-32 = 288 Hz. 1/2 of 288 is 144. 80 Hz is going to be a little to the right of 1/4 up from fully counter-clockwise on the knob.
The full range spans 320-32 = 288 Hz. 1/2 of 288 is 144. 80 Hz is going to be a little to the right of 1/4 up from fully counter-clockwise on the knob.
You can get an accurate setting with a DMM and an 80hz test tone. The procedure is similar to setting the gain with a DMM, first set the lp filter to its highest setting, then play the 80hz tone and note the voltage, slowly lower the lp filter until there is a 30% drop in voltage.