I would like to know what a producers role and responsibilities are in a record company to an artist and his record label.

You hear in some articles that a producer gets involved on song writing. some purley say that a producer simply records the sound and puts some tweaks in i.e. compression and EQ.

does an artist go to a producer and say ' i wanna do a rock tune ! ' . and then the producer liaises with the artist as to how to go about it?

or does the producers role and responsibilities change per artist?