Alsaequal is a real-time adjustable equalizer plugin for alsa. it can be adjusted using an alsa compatible mixer, like alsamixergui or alsamixer.

alsaequal uses the eq caps ladspa plugin for audio processing, actually alsaequal is a generic ladspa plugin interface with real-time access to the ladspa controls (the ladspa plugin included with alsa doesn't allow for real-time controls) but it was developed for and only tested with eq caps ladspa plugin.