I did a little test with our dogs. I wanted to test our dogs hearing.
Our yard is about 125 feet long. While the dogs were at one end of the yard I tried whispering something that would get a auto response from them, like "Go for a walk?" or "Car ride".
I tried to whisper it as quietly/low as I could without moving my lips.
I tried it several times and worked just about every time . Their ears perked up and sometimes their heads tilted. Then I tried it inside. As soon as I started whispering it really got their attention, it also got my kids attention as well.
So when you yell at your dog to get his attention or feel the need to repeat something - they heard you the first time. They are just ignoring you.
Next time you want your dogs attention try whispering to him.