Is there a way or a plug-in that will allow Audacity to do dynamic range expanding? I have hunted around and can’t seem to find anything.
There is the “SE4” by Steve Harris http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html#tth_sEc2.93
(I’ve never used it though, so don’t ask me how it works 
)
Chris Capel’s dynamic compressor (http://pdf23ds.net/software/dynamic-compressor/) might do what you want if you set the compression ratio to a negative number. --Allen
"FLOORFISH.dll " is a VST expander / noise gate that is said to work with Audacity. http://www.digitalfishphones.com/main.php?item=2&subItem=5
See here for other plug-ins: http://audacityteam.org/wiki/index.php?title=VST_Plug-ins