Fix frequency to level

The curve is shifted so that the specified frequency is given a specified value. In the figure below, the specified frequency is 1000 Hz and at this frequency the curve is shifted so the value is 0 dB.

Note: If the vertical axis is set to Linear or Squared (energy), the shift will still be given in dB, so a shift of 0 dB will give the value 1 at 1000 Hz if the vertical axis is Linear.