After 50 years, the only rule I know is that you have no idea what a producer is going to hear in your demo.

Some of the biggest hits have had gawdawful demos. You listen, knowing the hit and wonder how anyone heard that in there. Those, however, are the exception, not the rule.

For the most part, David’s advice is spot on. The demo must showcase the SONG, not your arranging skills, not the vocalist delivering it or anything that distracts.

As for engaging a “pro singer”, it depends on the singer. There are a few who specialize in demos and when you’ve heard enough, you know who they are even if you don’t know their names. In the ‘70s and ‘80s, it seemed like Livingston Taylor (Berklee prof and brother of James) sang over half of all the demos I heard. His voice sounds close to his brother but lacks the distinct personality. This lets the producer concentrate on the song.

Back to the OP, BIAB is very well suited for demos. I’ve used it for a few clients. There are hundreds of styles that don’t call attention to the arrangement if used with a bit of restraint. Unless there’s an instrumental as well as a vocal hook, skip the long introduction.

I don’t use it on my own demos but it’s because I’m too lazy to audition styles till I find what I like. If guitar, I have some tools that I use. For piano, when I was a Voice major, 50+ years ago, I met a Piano Performance major and a few years later we were married. I tell her what I need or write it out and she plays the way I want to hear it.

BIAB 2024 Audiophile Mac
24Core/60CoreGPU M2 MacStudioUltra/8TB/192GB Sequoia, M1 MBAir, 2012 MBP
Digital Performer11, LogicPro, Finale27/Dorico/Encore/SmartScorePro64/Notion6 /Overture5