A beginner chiptune composer sent me his music and I want to help him. I don't know any music theory basically. I compose by ear only and I usually can tell when an instrument is off key, but sometimes I'm not too sure. That's why I want your input. Do any of the following songs contain instruments that are off key (they all sound off key to me):
http://www.youtube.com/watch?v=gOx19aV2osg
http://www.youtube.com/watch?v=lghmdPCcvOA
http://www.youtube.com/watch?v=PvowcJBGioU
http://www.youtube.com/watch?v=ry3Hy0kckuM
http://www.youtube.com/watch?v=iA-jJfI8hLU
You don't have to listen to all of them. One or two is enough. If he made a mistake with one of them and didn't notice, that means he can't exactly tell when sounds are off key. I used to have that problem too in the beginning. Nowadays I figure out the key I want to use before I start a song, and that way I won't make any mistakes like that.