First of all, I really hope I'm in the right place, secondly, I know this is a difficult topic and many have tried figuring it out but can't find anything specific yet, so, here it goes:
What I am trying to do is build a service that accurately gives you the music that you want to listen (as other services tried but none has succeeded yet). One of the things I need in order to do that is a way to "calculate" the emotion that a song is exposing. For instance, I've read somewhere that usually a sad song will have its key in Am.
An even bigger stretch would be doing the same thing with the genre(pretty sure this isn't possible but if I'm wrong, and I hope I am, please correct me).
As an extra-description of what I'm trying to build, here are the main 2 problems that most services have are:
Hitting a "radio" button on a song will do one of 2 things: either start a playlist with just that artist or start a radio which randomly adds songs into your playlist, but if you start your playlist with Celine Dion for instance, 10 songs later you're listening to Rage Against the Machine (maybe because of wrong tags or something).
They are playlists so you end up listening to the same 50 songs when you could have thousands to pick from, so it's not random, and it's never new (don't you just get bored of listening to the same songs over and over again? I do).
There would be the third problem that it's all relying on user input, which is, unfortunately, rarely accurate and probably part of the previous 2 problems(wrong tags, playlists not being updated, etc).
So overcoming this would be the main focus of my project.
What I need from you guys (i know I might be asking to much) are some checkpoints:
Let's say, you wanna write a song about a love story, something romantic, what are the steps you take. Do you pick a specific range for the tempo? A specific key? Some specific progressions? Anything specific really. How about for a happy song? A drinking song or something that suggests confidence? The more "emotions" the better, anything that could help me narrow things down.
Let's say that the main emotions that I'm interested in are:
You don't have to stop at this list, anything else you can think of is highly appreciated. I know things might be repeating between them, and I understand that even if there would be a "rule" there would also be exceptions, but I am hoping to find a pattern in your answers, a starting point that I could later test and "tweek" :).
How about for the different genres? (I know for instance that in "the old days", hip-hop usually had its tempo set around 90bpm? something like that..)
Another helpful thing would be a list of properties for songs/sounds (like pitch, tempo, key, etc.. ).. maybe a short definition of that property (i'll get most part by google searching it, so I don't need you to do everything for me but a start would be highly appreciated) :).
Hope this will drive this discussion into a more technical/expertise driven one.
Thank you all in advance and I really hope I'm in the right place. If not, please let me know and I'll delete the post straight away.
Edit: I understand there isn't a 100% formula for this matter and that subjectivity has its part, but I am looking for any clues that I could look for.