Here is the vid of my buddy’s silver truck and my red truck with our air horns.
Silver has K3’s 1/2" ID running 150 psi
mine are K3’s 3/8" ID running 200 psi
i think mine are higher pitched because of 200 psi.
Nice trucks & nice hornage.
The horns are probably tuned a little different. Even as your pressure dropped through the video, the pitch was still higher than his.
we compared horns, we had the same bells.
maby cuz mine is powder coated and his are bare?
The same bells are often tuned different. Some people go through the trouble of tuning them. For instance, adding or removing material from the depth of the bore in the power chamber.
That silver and blue truck looks really nice.
lol thats becase its yours! 
Welcome to the forum “Loweredhemi”.
Thanks, hope to get some good ideas of things I can do.