Apparently, the sound travels at 768 miles per hour, but the sound reaches the competitors in the back lanes a few milliseconds before those closest to the pistol. I clearly do not know much about the Olympics, but apparently, the few milliseconds make all the difference in the world when going for the gold.
Some events have tried to compensate by having extra speakers behind the runners, but that can mix them up. Fortunately, Omega figured out that an electric beep played only through the speakers behind each starting lane levels the playing field. The gun that you see in this picture is only there for show, and when the trigger is pressed, this is what makes the beep and then starts the clock for the runners.
I believe this tech has been used in swimming for over 20 years. Personally, I welcome technology that improves our lives, even if a little sports tradition like a starter pistol gets the shaft.