Pontiac 2006 GTO Owner's Manual page 151

Speed-Dependent Volume (SDV)
With SDV, the audio system adjusts automatically to
make up for road or wind noise as you drive.
This feature will never completely compensate for
driving noise. There are other factors such as road
surface, wind noise, windows open, and engine speed
that may alter the interior noise for any given road
speed.
You can select compensation rates between 0 (off) and
5 (maximum compensation) in the options menu.
See "Options Menu Adjustment" later in this section to
adjust SDV.
Dynamic Distortion Limiting (DDL)
The radio has a feature that limits the amount of
amplifier distortion that you can hear. When this feature
is turned on, it continuously monitors the quality of
the signal to the speakers. When the signal distortion
exceeds the preset limits the radio will automatically limit
or reduce the volume until the distortion is minimized.
Under some circumstances, distortion may be heard for
a very short period of time until the system has taken
the necessary steps to limit it.
The speakers may go off when the volume level is set
at a high or full volume for a long period of time in order
to protect the amplifier from overheating. When the
amplifier cools down, the radio will reset and you will
again hear sound through the speakers.
The main source of distortion in music is the low
frequency bass caused by drums or large instruments.
Music that features very strong bass may trigger the
distortion limiting system and the system will then
reduce the volume to minimize the distortion. Increasing
the bass control or the EQ boost may also result in a
reduced volume level due to the emphasized bass. See
"Setting the Tone (Bass/Treble)" previously in this
section. The DDL can be turned off so that the radio will
deliver a higher volume level, but distortion will also
be increased.
See "Options Menu Adjustment" later in this section to
adjust DDL.
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