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Vocal production is the first step from demo recording to radio-ready recording. A song with a well-recorded, well-mixed, and well-arranged vocal is so much more valuable than a song with a crappy vocal, even if you have nothing but a simple guitar or piano as instrumentation. It really is the best bang for your buck. The fun bit is that it's not at all hard to upgrade the quality of your vocal recordings. All you need is a decent mic, a cheap interface, and some practice. Hell, I record all my vocals with gear that isn't worth more than $1,500, and I'm making my living with this. Pretty good investment, I would say.
The thing about vocal production is that most people hate doing it. Songwriters hate it because it's technical, and beat producers hate it because the human voice is an instrument that's difficult to understand unless you're a singer yourself. There's an art to working with singers, getting the best emotional performance out of them, and then spending hours per song on editing the takes, pitch-correcting the vocal, and using post-production to end up with a vocal that sounds like it was recorded in a million-dollar studio. Except it wasn't. Booyah!