The clarinet is a woodwind instrument with a single reed interface. It can be found in Conflass Gardens(?) and brought back to your base.
At night, instead of spending experience points on upgrading a stat, you can practice the clarinet. Mastering the clarinet is a long and arduous process, taking ten or so days to master.
After you max out your clarineting skill, your character will blame his ineptitude on his stubby fingers and wistfully states how he will never be able to play at Albert Hall.
It appears that the clarinet does nothing as of now.