Some laptops have a mixer chip that is not recognized by default. For example on this Samsung Q35 this is required in /etc/modprobe.conf
options snd-hda-intel index=0 single_cmd=1 model=laptop-eapd
-Andy
the strange thing is that it was recognized and working fine with the 2.6.9.34.0.2 release of the kernel .... and if I reboot with the old release (2.6.9-34.0.2), it works ....