SOUND_MIXER_IGAIN
type = SOUND_MIXER_IGAIN;
idat &= (1 << SOUND_MIXER_MIC) | (1 << SOUND_MIXER_IGAIN);
#define SOUND_MIXER_READ_IGAIN MIXER_READ(SOUND_MIXER_IGAIN)
#define SOUND_MIXER_WRITE_IGAIN MIXER_WRITE(SOUND_MIXER_IGAIN)
#define SOUND_MASK_IGAIN (1 << SOUND_MIXER_IGAIN)