From the ALSA wiki
There are two ways of getting Linux drivers to work, you can either compile them into the kernel or build them separately as modules. Read the Kernel-HOWTO for details of how to compile a kernel.
You must turn on the sound support soundcore module
This is in the kernel. Look in the sound drivers submenu and it should be the first option ("Sound card support", CONFIG_SOUND). Most people enable the module setting. That way you can load and unload the module manually if you have multiple soundcards or if you intend to debug or use cutting edge software which may cause your drivers to halt sometimes. Of course it also means you have more control of your system. Most modern distributions come with soundcore compiled as a module. You can check this in numerous ways. The easiest way is to type.
modprobe soundcore lsmod | grep soundcore
If this command returns that you have this module, then you don't need
to recompile your kernel. Some Motherboards don't do a very good job of
assigning irq resources. You may want to do
cat /proc/interrupts to
see what irq numbers are assigned to what devices. Often, irq 9 provides
the best performance for usb needs. As an example:
CPU0 0: 387086 XT-PIC timer 1: 5528 XT-PIC keyboard 2: 0 XT-PIC cascade 8: 570892 XT-PIC rtc 9: 352520 XT-PIC usb-uhci, eth0 12: 130823 XT-PIC PS/2 Mouse 14: 9218 XT-PIC ide0 15: 26 XT-PIC ide1
Retrieved from "http://alsa.opensrc.org/Introduction"