Treat Harsh Vocals: To soften vocals apply cut in a narrow bandwidth somewhere in the 2.5KHz to 4KHz range.”

This is where a lot of what is being done is dependent on the type of mixer you have.  For example, if you run an analog mixer, you most likely have a semi-parametric EQ.  This means you EQ via knobs on each channel with control for gain (amplitude) and the center frequency, however, you can’t control the width of the affected frequencies – the bandwidth.  Thus, your EQ adjustments affect a wide range of frequencies at once – like moving a mountain peak back and forth – it means you have to move a lot of the mountain with it.

Some EQ’s allow the user to work on EQ like a surgeon, making freq cuts/boost in very specific ranges. Harsh vocals can be reduced by sweeping over the mid/ high-mid frequencies until you hear the harshest vocal sound.  Then you cut (reduce) those frequencies via the EQ.  This would be the case with a parametric EQ where you can control the center frequency, the gain/amplitude cut or boosted, and the bandwidth, sometimes known as the Q.