Hi -
I am trying to record a radio podcast, with music played from MP3s and voice/conversation but have one problem.
How do I control the mic recording volume so that when an mp3 plays Audacity only records that and not the mic or keyboard clicks?
Thank you. 
Iāve been known to use a small mixer.
http://kozco.com/tech/audacity/pix/UniversalPodcast-I.jpg
Ignore the computer on the right. The left computer is playing music into the mixer from whatever app I choose, currently iTunes. The Microphone (headset type, on the left) is plugged into channel one of the mixer and the balance between microphone and anything else thatās plugged into the mixer is a simple matter of adjusting each channel volume. During the intro or outro, the microphone fader is down and just the music plays. Then bring the microphone up and the music down slightly so you can ātalk overā the music and then fade the music all the way out if thatās what your show calls for.
The other half of the computer is recording the mixer output in Audacity. I set Audacity sound levels and the mixer levels the same and then do everything else from the mixer using the mixer sound meter.
There is a USB version of that mixer for the Windows people or those with newer Macs without Stereo Line-In.
The computer on the right is for Skype. I didnāt get that far yet.
Koz
Thank you. I will give it a shot
Actually, I was hoping to find a solution on the Audacity software. Unlikely to get a mixer for a while.
What kind of microphone? Doing multi-point sound channel management on one computer can be insanely complicated. If you have a USB microphone, I think you may need to be in the Windows Control Panels to change the microphone volume without changing anything else. Some microphones let you switch the microphone off at the head.
Thatās why the mixer is so handy.
Audacity will not be of any help with this. Audacity does not make any changes to the sound during recording. You have to do it in the computer or extra software/hardware that you added to the computer.
Koz