Now that Rhythmbox is the default music player in Ubuntu 12.04, it's probably worth getting the best out of it. One notable absentee from the shipped application is an equalizer. You can install this plugin individually or you can install a range of working plugins from a ppa mainatined by fossfreedom.
To install the complete collection of plugins, add fossfreedom's ppa. Open a terminal and type:
sudo add-apt-repository ppa:fossfreedom/rhythmbox-plugins
sudo apt-get update
Then install the plugins with:
sudo apt-get install rhythmbox-plugin-complete
Once installed, open Rhythmbox and click Edit and then Plugins: check the Equalizer checkbox and you're done.
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