Usually, anyone who "thinks" they want to sit in on a mixing session will very quickly figure out that it's not particularly exciting to watch.
People forget that it is, after all is said and done, just work. Just like with anything else. Would you want to sit around for several hours and watch a grocery store clerk in action?
I mean ... yea, sure it would be fine if it was all fun stuff like putting wacky effects on things, etc. But for the most part, a typical mixing session is going to involve plenty of unglamorous, non-sexy tasks. Do you really want to hang out while I test out various gate thresholds ... attack/release times on compressors, silence breaths, work out crossover points for multiband compression?
Be prepared to get plenty bored.
Then there's the question of just how effective am I going to be with someone watching me work the whole time? Remember, to the guy mixing, it is "work." It's a job, and I don't know about you, but it gets nervewracking to try and work while someone is looking over your shoulder ... watching, staring, while you pick your nose, scratch your nuts, etc. Just quit staring at me, for cryin' out loud. Go have a smoke, take a walk ... get some food; aren't you hungry?
Pick some coffee up for me while you're at it.
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