CyanogenMod’s DSP equalizer provides gives enhanced sound processing capabilities. It has ability to adjust audio parameters such as bass boost, 5 band equalizer, virtual room effect for all system audio.
When you are on the stock ROM, one of the major feature you might be missing will be CM9 DSP Manager. There is a SoundFX app with ICS, but it is now way near CyanogenMod’s DSP equalizer.
To install DSP Manager, download the following file and flash using ClockWorkMod or any other recovery of your choice.
NB. You need Busybox installed.