[alsa-devel] Where to find a guideline for ALSA mixer and control interface?

Could someone tell me where to find a guideline on how to use ALSA mixer & control API? Is reading the source code of amixer my only choice? But I want to have a big picture about these API at first. Many thanks!

I found there are many online documents about PCM interface but few about mixer or control interface :(

Thanks & Best Regards Mengdong