As you probably know, iTunes does have its own sound equalizer to adjust frequencies, bass, treble, and other audio settings. But what about a general audio equalizer that works with any application? eqMac is a system-wide audio equalizer that will allow you to equalize any audio playing in your OSX.
The application comes with some built-in presets, but you can also adjust each frequency individually. It’s needless to say it will barely notice any difference if you’re listening to some music through your MacBook’s speakers. This application is recommended for those who own nice speakers or headphones.
eqMac is available here.