At my high school, we have a very strange auditorium, with strange acoustics. They once had a professional bring in an RTA, (which came up with some pretty strange frequencies), but since then, our GEQ has been messed up, so now all the notches are just at 0. I am looking for a completely free or extremely cheap RTA sort of system. I found this online which is (according to my own unprofessional, inexperienced opinion) pretty good. I also have this little program which outputs pink noise, or white noise, or whatever. So, I've got pink noise, an RTA, but no measurement microphone. What I'm wondering is, can I use a different microphone, and just adjust the system. I could use an SM58 mic (edit,: or rather our MKE-2 since it is omni), output white noise, and fix the EQ to match the picture of the SM58 (MKE-2) frequency respone. ...right? Is there a better way of doing this? Is there maybe a different program out there that just let's me tell it that I am using an SM58, and the computer calculates it accordingly? I also have a RadioShack decibel measurement device with a microphone and an output. Is this maybe flatter, and thus better to use as a measurement microphone. (I just don't know how much to trust the quality from RadioShack) I'm kinda lost here, so any information is helpfull.