mixer.exe is a part of the drivers for the C-Media onboard sound systems. It provides the user with a replacement for the default Windows Volume Mixer.
Non-system processes like mixer.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues