The legendary announcer was eliminated off Fox's "The Masked Singer" this week ... and as it turns out, the dude can sing pretty well!!

Buck -- who lasted 2 episodes -- put on an impressive rendition of "I Want You to Want Me" by Cheap Trick to start off his experience ... but no one knew it was him at the time.

But, fans finally got to meet the man behind the mask on Wednesday ... and it turned out to be none other than one of the most famous voices of the NFL and MLB.

Buck's stunning reveal came as a shock to many ... except for one judge -- Eric Stonestreet, who said he knew it was Joe all along.

FYI -- Joe works with Eric on the show "Domino Masters" ... so the two are familiar with each other.

52-year-old Buck says he wanted to do the show because he had a paralyzed vocal cord 11 years ago ... so singing on the show was fulfilling a personal goal for him.

Check out the video -- Buck had some pretty creative clues about who he was throughout the show ... and seemed to really be enjoying himself on stage.

But, don't fret baseball and football fans -- the 8-time Emmy award winner and iconic play-by-play guy isn't leaving the booth to be a singer.