This crossbow is rather loud. It makes a good "THUNK!" when shot. I have no way to measure velocity. I also use selfbows that I make, and in my opinion & experience, shooting a wooden/bamboo arrow from a wood bow is just about the quietest thing out there. All you hear is just a small "snick" sound upon release. A loud bow can be heard by deer, and if it is coiled up or tense, a deer can easily "jump the string" by suddenly crouching down, then bounding away. Often, your arrow will fly over the top of them as they crouch down.
My Excalibur is also noisey. I also hear a lot of critics talk about a deer "jumping the string" when they hear what sounds like a hammer smacking a piece of plywood.
The velocity on my crossbow arrow is 300 FPS. It's accurate enough that I feel confident at taking a shot at a relaxed deer at 50 yards. My furthest shot at a deer that I took was at 35 yards.
For the purposes of this analysis, let's use 50 yards. I don't know what the downrange velocity of the arrow will be at 50 yards but let's use a conservative estimate and say the arrow is going 200 FPS when it hits the deer at that distance. So the average speed between zero and 50 yards is about 250 FPS.
So from the time the arrow is released until it hits the deer it is going to be (50 X 3) / 250 = .6 seconds.
The speed of sound at sea level for a standard day is 1120 FPS. The speed of sound is dependent on temperature. So with a 45 degree day, the speed of sound is about 1100 FPS. With a 50 yard shot, the deer will hear the crossbow (50 X 3) / 1100 = 0.14 seconds later.
After the dear hears the crossbow, the arrow will go through it .6 - .14 = .46 seconds later.
I will concede that if the deer is looking at you when you take the shot there is a possibility of it moving to get away. However, if it has it's head down and eating acorns or looking away, it's not going to "jump the string."
Also think about how a deer's legs are made. The legs are almost like ours and with knees. Try jumping from a flat-footed position WITHOUT bending your knees. It's impossible. In order to jump from a standing position, you have to bend the knees first then extend them rapidly to jump.
A deer has to do the same thing. Even to start a run from a standing position, the deer has to start with bending its knees in an effort to begin forward movement.
So with all that said, a deer isn't going to "jump the string" if it hears the smack of a loud crossbow. So I raise the BS flag anytime I hear someone, who doesn't like crossbows, talk about stuff he knows nothing about.
I'll have to verify my theory with all the deer that have been killed with a crossbow.
Sorry for the rant but I wanted to put this "jumping the string" theory to rest and provide you information if that subject ever comes up in your hunting circles.