Listen to the difference between super-sonic 124 grain 9mm projectiles and the same projectiles loaded to speeds which are sub-sonic.
The first 3 rounds in this video are super-sonic, followed by 2 sub-sonic, 2 more super, then the last 2 sub-sonic again.
The sonic "crack" of the super-sonic bullet flying through the air actually makes more sound than the report from the suppressed pistol which is firing only @ 30 feet behind the video camera. THIS is proof why suppressors really work best for sub-sonic loads and this is why a suppressed high power rifle is only really good for protecting the hearing of the shooter from the muzzle report.
Tragic events like the one in Vegas recently support the proofs that this video details in that most of the eyewitness videos which were taken on the ground at the Route 91 Harvest concert mainly record those incoming projectile's sonic "crack" than they do the report from the un-suppressed rifle off in the distance.
People, if you ever hear similar "cracks" around you, even if you don't hear any actual gunfire; GET DOWN, YOU ARE BEING SHOT AT!