I was just having a terrible problem with exporting from Audacity to create an mp3 on the Intel Mac. The lame download from the site is fine. The problem is that you don't really know what you need in the end so when Audacity asks you to find it, you don't know what you need.
The file's name is libmp3lame.dylib. So when you download it from the site, you will probably get a folder named: libmp3lame-osx-universal-3.97. The way I solved it, was to simply put this whole folder in my Audacity application folder. When I chose File>export as mp3 and it asked me to find the lame file, this is how I navigated: the folder>package>usr>local>lib and sure enough there was the file. Once it is located, you will never have to do it again. If someone has a better or more efficient way, I'd like to know!
Audacity Mac Intel
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