What should you do if there is harshness in the vocals? Let’s say the vocals were harsh in the 9 – 10 kHz area and you want it to sound a bit smoother? Note that harshness is generally found in the 2.5 kHz area. However, you have to consider the harmonic multiples as well, so it’s not surprising that the 10 kHz area (2.5 kHz * 4) will add its own harshness.
You may use a multi-band compressor with only the top-band activated. This way the compressor leaves the entire signal alone, except for region above 9 kHz.
Read more about this here: https://www.audio-issues.com/music-mixing/3-ways-to-reduce-harshness-in-your-vocals/