I have installed CentOS 6.5 on a Dell Insperion with an Intel chip. I first noticed that my microphone is not working on Skype on CentOS although it was working fine with Windows 7 on the same box. The speakers work fine on both operating systems. I did the following test.

Code:
arecord -vv -d 10 test.wav
aplay -vv test.wav
and did not get any sound played back. I went to System:Preferences:Sound to get the Sound Preferences dialog. I went to the Input tab and "Microphone" was selected as the connector. I turned the input volume up to maximum and spoke into the microphone but the "Input level" boxes all remained a light gray like it was disabled. The only option for "Choose a device for sound input" is "Internal Audio Analog Stereo".