My band played a gig a month ago and the clubs owner said he can record us and he did with a really nice quality but our problem is :the vocals are too loud

when our singer and me (backing vocals) sing you can hear neraly nothing of the rest.

We've only got it was an MP3-file

is there any possibility of turining down the volume for the singer?

btw:we only have guitars drums and bass
Nope. At the very least, the vocalists would have to be on their own track. That would allow you to remix the entire thing and fix the hot vocals. As it is, you're stuck.
Not really. You could try using EQ to tame it a little, but there's not way to just turn down the volume.
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Did you record it all together? or seperate? If seperate, tell him to turn the vocal tracks down. If you didn't record them seperate, I've always found when doing live stuff, add the vocals in later. That way you can get a good a mix out of a live demo.
But apart from that, you can't do anything with it.
Post it up for download to see if any of us can work any magic?

I know there are at least a few people in the forum who could give it a good go.
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Lost cause. I wouldn't even try.

Could I get some more talent in the monitors, please?

I know it sounds crazy, but try to learn to inhale your voice. www.thebelcantotechnique.com

Chris is the king of relating music things to other objects in real life.