In this section you will find parameters related to your sound equipment.
In linux, you have two different kinds of soundcard drivers: OSS (called also kernel drivers) and ALSA. A program can use ALSA driver the same way as OSS ones, but ALSA drivers have better performance when used passing trough the ALSA library. So if you have alsa drivers (names begin by snd_*), select the ALSA mode. If you don't know, choose OSS.
In this combo box you can choose the recording source for your voice. In most case it will be the microphone (mic).
By toggling this option, linphone will try to stop sound daemons (esd and artsd), that may lock permanently your audio device, and so cause linphone to fail in open the audio device when it needs it. It is recommended to have this option on.