Sorry but this is wrong. You dont chose a time signature, in a way it choses you. I have never came accross a composer who will choose a time sig then write a riff around it. When you compose a riff it will automaticly fit into a time sig. You dont CHOOSE what the time sig is, it just is. You cant have a 4 crotchets in a 4 crotchet beat bar and say it is in 6/8, music dosnt work that way. Im not being a dick or anythig but thats just music.