Asus V3-M2V890 - Manual (Page 57)

4-11 ASUS V-Series M2V890
10. Optical drive audio In connector (4-pin CD)
This connector allows you to receive stereo audio input from sound
sources such as a CD-ROM, TV tuner, or MPEG card.
CD
Right Audio Channel
GND
GND
Left Audio Channel
Internal audio connector