My Soundchip (X31):
0000:00:1f.5 Multimedia audio controller: Intel Corp. 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) AC'97 Audio Controller (rev 01) Subsystem: IBM: Unknown device 0534 Flags: bus master, medium devsel, latency 0, IRQ 5 I/O ports at 1c00 [size=256] I/O ports at 18c0 [size=64] Memory at c0000c00 (32-bit, non-prefetchable) [size=512] Memory at c0000800 (32-bit, non-prefetchable) [size=256] Capabilities:  Power Management version 2
This seems to be a combined Modem/Sound chip, ALSA uses module "snd_intel8x0".
No its not missing, all the above tells you is that you have a PCI to AC'97 Audio interface in your machine, it does not tell you what the actual audio codec is. If you look at the X31 page you will see a link to AD1981B which is your audio codec.