Equalsa is An equalizer for ALSA. Supports command line and GUI interface. Works by automatically editing the .asoundrc file. requires: Python and swh-plugins package. For GUI: PyGTK, Glade
JEQ is class library written in pure Java. It implements the infinite impulse response (IIR) algorithm for bandpass filtering of sound stream. So, it represents a backend code for stereo 10/15/25/31-band equalizer.