Ask the producer.

If you are producing yourself, I think you might know the answer to your question. Trust your ability in yourself and your instincts. It comes with time and experience and confidence. Set limits on your project in terms of your time as if it were money ... because it is. The point of greatly diminishing returns on your time comes pretty quickly. It's important to work quickly and then move on. Learn to let go. And yes, I realize this advice is easier said than done. Best of luck!

Jon

I try to take a five minute break every hour or two and get away from the mix. When I come back I'll listen to it away from the mix position and see if anything jumps out at me. I'll go back and make some changes. I'll repeat that process a few times until nothing jumps out as being horrible. That's when I print the mix and either pull the patchbay or move onto the next song.

Trust yourself!
Compare your mix to cds that you like.
Don´t mix too loud.
Use headphones too, sometimes they tell you better where you have to go.
There are no hard rules in mixing/recording.
I always route the pro tools tracks to analog mixer for mixing, at least for pop/rock it really brings more life to the mix instead of doing it internally.
Read books about mixing (there´s plenty around), ask questions whenever you can.
It takes years to become a good mixer, take your time!

When all the red parts have become black and crispy and the mandolins sound bigger than a Bosendorfer on steroids. Or when it sounds great to you.
Jim

PS - If your tracks don't have mandolins then the mix is not done. Admit it, aren't you always thinking, 'if this track just had a mandolin or two, it would be finished'

Tony Clarke once told me that he thought the principal impact a producer could make was deciding when it's done. It's very easy to go past the peak of performnce at almost every step of the way.

Bob wrote: "It's very easy to go past the peak of performance at almost every step of the way."

Well said, Bob, and so very true.

Jon

Yeah especially when its all in a DAW and automation is so easy and you just keep coming back making changes. Lately i've been finding how much better my stuff sounds when I compress and eq going in and not using many plug ins in the mix. Now im just trying to leave the faders at 0 and record everything that i way i want it to begin with.

"When is the MIx done?"
When the client runs out of funds--and the project is no longer fun ,,,,,,,

Mixing is like painting. You are never finished, you just stop.

That said, knowing when to stop is the difficult part.

If you find yourself mixing again to change single notes on a project that already sounds good, you are into minutiae, not music.