A research project by a student (Ian Simon) and a Microsoft empoyee lead to a nice toy called MySong. This software analyzes the melody of a vocal track and automatically creates a musical accompaniment:
MySong […] automatically chooses chords to accompany a vocal melody, allowing a user with no musical training to rapidly create accompanied music. MySong is a creative tool for folks who like to sing but would never get a chance to experiment with creating real original music. Come on, you know who you are… you sing in the car, or in the shower, or you go to karaoke clubs, or you just once in a while find yourself singing along with catchy commercial jingles.
Here is a short video which demonstrates MySong:
For those who can’t/won’t watch the video, here a short description: At first, you sing a melody into your microphone. As soon as you’re done, MySong builds a chord sequence around it. You can influence the style a bit with two sliders. You can decide whether the music should sound more sad or happy and whether it should be normal or jazzy.
MySong’s creators emphasize that their program is not meant to automate songwriting. Nobody will ever create a top 40 hit using any version of MySong. It is rather meant to at least give people an impression of how it feels to write a song. It should also be good enough to produce a birthday or valentine song.
Unfortunately, the program is not available for download. I hope Microsoft doesn’t let it rot in the drawer…
The website also has an article of a scientific journal which describes the theories behind MySong in detail. There’s also tons of samples.