Stuck? Work harder. Find workarounds. Collab. Youtube. Take a small break do something else. Then another night of hours staring at the screen mixing, arranging etcc.. Sure you will feel stuck. But keep on broadening your horizon.
If you give up after 2 hours thinking your beat or mix suck, then remember this:
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"Max Martin and writing-producing partner Rami use the same standards when they apply the musical cosmetics — mixing, polishing and layering vocals and instrumentation. "It's sick," says Martin Dodd, a longtime friend and head of A.-and-R. for record label Zomba Europe. "They'll stay up literally for three days just to get a drum sound right." Even then, songs don't always turn out as planned. With the mixing of Oops! ... I Did It Again, "after a week, Rami and I realized it sounded like shit," he says. "It didn't groove." So they scrapped it and went back to bar one. Two weeks of 18-hour-plus days later, the song was done. "It wasn't that we had an extreme deadline," Martin says. "That's just when you get psycho. That's when you get manic.""
(From Time magazines article Top of the pops)
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Wanna give up? Sure, patience isn't for everyone.
Wanna be good at it? Keep on mixing. For days/weeks/months/years. Learn and earn.