OK guys... what do you reckon to this one?
I'd like to help but my current level of expertise would probably lead me to incorrectly diagnosing the problem and therefore coming up with the correct sollution.
However, I'll try to help and hopefully someone will step in and correct me.
Our new friend says that the hi-hat sound is too loud and that sometimes the volume decreases. Is this a bad recording? I can't see how it can be to be honest... you set up the mic and then it would then be a question of dynamics (how hard the hi-hat is hit). If it is dynamics then why would we want to change this during mastering?
If we still wanted to change this in mastering then would the answer be a multiband compressor? Home in on the hi-hat frequency on compress that to tone down the dynamics?
Personally I don't think it's workable but I'll be interested to hear what others think...