Q. A publisher wants to hold my song for three years while they try to sell it to artists. A simple song agreement shows only an intent to sell. A. A producer is the person responsible for the overall sound of your project. This can include obtaining the proper musicians for your project, material development and all stages of recording and mix-down. That doesn't mean they personally do it all, their just responsible for it.
Great producers have an intangible knack for creating projects that intrigue the public.
A good example of a great producer that literally made a band out of almost nothing would be producer George Martin and The Beatles. More information about a producer's role. More information on a music producer's role. That's why you hire a producer. They are responsible for getting the sounds and ideas in your head into a tangible form.