http://musictheoryworkshop.com/music-theory-keys-lessons/ Commonly only a few key signatures tend to be picked up, and the notion of learning all of the keys just plain scares people. It doesn’t have to be that way. Any Key Signature has quite a few scales you can use. However the manner keys are taught, it requires a very long time to know all of them. This doesn’t have to be difficult either. A concentrated approach gets results when used will increase your learning routine.
