Chevrolet 2002 TrailBlazer Owner's Manual page 218

Setting the Tone (Bass/Treble)
AUDIO: To set the bass, press the AUDIO control until
BASS appears on the display. Turn the control to
increase or decrease bass. When you use this control, the
radio's tone setting will switch to custom.
To set the bass to the middle position, select BASS and
press and hold the AUDIO control. The radio will
produce one beep and set the display level to zero. To
set all tone and speaker controls to the middle position,
press and hold the AUDIO control when no tone or
speaker control is active. The radio will produce one
beep and CENTERED will appear on the display.
To set the midrange, press the AUDIO control until MID
appears on the display. Turn the control to increase or
decrease midrange. When you use this control, the
radio's tone setting will switch to custom.
To set the midrange to the middle position, select MID
and press and hold the AUDIO control. The radio will
produce one beep and set the display level to zero.
To set all tone and speaker controls to the middle
position, press and hold the AUDIO control when no
tone or speaker control is active. The radio will produce
one beep and CENTERED will appear on the display.
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To set the treble, press the AUDIO control until TREB
appears on the display. Turn the control to increase or
decrease treble. When you use this control, the radio's
tone setting will switch to custom. If a station is weak or
noisy, you may want to decrease the treble.
To set treble to the middle position, select TREB and
press and hold the AUDIO control. The radio will
produce one beep and set the display level to zero.
To set all tone and speaker controls to the middle
position, press and hold the AUDIO control when no
tone or speaker control is active. The radio will produce
one beep and CENTERED will appear on the display.
AUTO EQ: This feature allows you to choose preset
bass, midrange and treble equalization settings designed
for country, jazz, talk, pop, rock and classical stations.
The setting last chosen will appear on the display when
you first press AUTO EQ. Each time you press this
button, another setting will appear on the display and
AUTO EQ will switch to one of the preset settings
previously listed.
To return to the manual mode (CUSTOM), press the
AUTO EQ button until CUSTOM appears on the
display. Then you will be able to manually adjust the
bass, midrange and treble using the AUDIO button. To
find out how to do this, see Setting the Tone following.