The control interface is used widely for many switches, sliders, etc. which are accessed from user-space. Its most important use is the mixer interface. In other words, since ALSA 0.9.x, all the mixer stuff is implemented on the control kernel API.

ALSA has a well-defined AC97 control module. If your chip supports only the AC97 and nothing else, you can skip this section.

The control API is defined in <sound/control.h>. Include this file if you want to add your own controls.