First download alsaequal:

# tazpkg get-install alsaequal

Then create a /home/tux/.asoundrc file:

ctl.equal {
  type equal;
}

pcm.plugequal {
  type equal;
  # Modify the line below if you don't
  # want to use sound card 0.
  # slave.pcm "plughw:0,0";
  # or if you want to use with multiple applications output to dmix
  slave.pcm "plug:dmix"
}

pcm.equal {
  # Or if you want the equalizer to be your
  # default soundcard uncomment the following
  # line and comment the above line.
# pcm.!default {
  type plug;
  slave.pcm plugequal;
}

Change (cd) into your music directory and then run:

$ mpg123 -a equal *

Or

$ mpg123 -a equal track1

Now you should be able to open up a separate terminal and use:

$ alsamixer -D equal

Just edit the audio_output section of your /etc/mpd.conf:

audio_output {
	type		"alsa"
	name		"equal"
	device		"plug:plugequal"
##	format		"44100:16:2"	# optional
##	mixer_device	"default"	# optional
##	mixer_control	"PCM"		# optional
##	mixer_index	"0"		# optional
}

And start/restart mpd and you should be able to use $ alsamixer -D equal

Copy the config.example file in /usr/share/doc/moc to your ~/.moc folder:

$ cp /usr/share/doc/moc/config.example ~/.moc/config

Then change the alsa output device line to:

# ALSA output device
AlsaDevice    = equal

And then start/restart moc.

http://www.thedigitalmachine.net/alsaequal.html