eqMac
macOS System-wide audio equalizer & volume mixer
.... Expert EQ, unlimited bands, fully customizable (Filter Type, Frequency, Gain, Bandwidth). Volume mixer, apply different volume levels per each application. Fully customize the look and feel of eqMac by changing the User Interface Colors, Feature visibility, and arrangement. Control all aspects of eqMac through a WebSocket API. Works with any programming language that supports WebSockets.