Another try. Let's say you selected 1.5 khz with the frequency control.
If you turn the bandwidth control fully clockwise, you would be cutting to boosting the only 1.5 khz frequency.
If you turn the bandwidth control fully clockwise, you would might cutting to boosting from 1.2 khz to 1.8 khz (a wider frequency range surrounding the selected frequency.
I don't know the exact specs on this, so I'm just giving you an example of narrow vs. wide bandwidth.