Audacity is a free and open sound editor that works on many platforms, including OSX. It is capable of recording and editing vocals and music. However, because of the broken patent system in the US, you cannot open or save files in MP3 or M4A format. The workaround is to download the encoders from a country where the patent system isn’t broken and install them on your computer. The download process is simple. From the Preferences-Libraries section of Audacity click on the Download button for either of the Libraries. It should take you to this page. Follow the links to the download site and install the libraries. Unfortunately, Audacity doesn’t find the new libraries when using Mountain Lion (and I suspect the same is true on Lion). And when you try to find them manually, you can’t see the /usr directory where they are located. There is a simple fix that requires a single line in the terminal.
Open the terminal and you’ll see a command prompt. It should look something like this.
macintosh-users-computer$
Copy text after the $ on the line below and past it after the $ in the terminal.
macintosh-users-computer$ sudo defaults write com.apple.Finder AppleShowAllFiles TRUE
You will get a prompt for your password. Enter your user password for the Mac.
Now restart the finder by going to the Apple in the top left of the screen and clicking on Force Quit option. Click on Finder and then choose Relaunch. The screen will go blank and all the icons will disappear. When they return open the Preferences-Libraries section of Audacity, click on the Locate button to locate the MP3 library and browse to the folder /usr/local/lib/audacity/. You’ll see a file called libmp3lame.dylib. Choose it. Restart Audacity and both the MP3 and FFmpeg libraries should show up.
Now go back to the finder and use the up arrow key to show the previous line. Backspace to change TRUE to FALSE and hit Return. Restart the finder and everything will be back the way it was.