Is there an app that creates a system-wide audio equalizer?

Solution 1:

Check out Boom, it's quite awesome.

Boom boosts the volume of your Mac at all levels. From boosting the volume of your music on iTunes, it boom the YouTube videos playing on your web browser. You can now boost the volume of any application playing sound or video like QuickTime, Podcasts, Skype, iChat, DVD Player, Garageband, iMovie and so on.

Solution 2:

I didn't want to pay to have an equalizer so I developed my own one and giving it away for free! Click here to download eqMac! The app is signed by Apple and works for OSX 10.9 and higher!

Solution 3:

There's a free method using Soundflower and an Apple Developer Application called AU Lab (you'll need a free Apple Developer account get it, search for "AU Lab" after login).

Basically:

1. Install both programs
2. Change your audio output to Soundflower in System Preferences
3. Open AU Lab and pipe the Soundflower signal to your audio out.
4. Apply an AUGraphicEQ filter in AU Lab
5. Fiddle with levels to your heart's content.

This solution was taken from a blog post at Dctr Watson. That page also contains better instructions and a startlingly informative comment thread.