The Frequency control lets you set the center frequency for the high frequency band (Peak or Shelf EQ).
The Gain control lets you boost or attenuate the corresponding frequencies for the high frequency band.
With the high band EQ set to Peak, the Q control changes the width of the EQ band. Higher
Q values represent narrower bandwidths. Lower
Q values represent wider bandwidths.
With the high band EQ set to Shelf, the
Q control changes the Q of the shelving filter. Higher
Q values represent steeper shelving curves. Lower
Q values represent broader shelving curves.