What is an easy way to know what key a song is in? I remember seeing either a post on the forum or comments under one of Pebber's many great youtube lessons where there was a discussion that if a song had a D & G in it the key would be in A (for example, may not be correct & all of the examples/keys were based on three chords/notes) and I thought that was an easy way to go about it. Suggestions?