Here is my two cents from hunting... mostly calling, only got one tag in 10 years, bulls in AZ, I have also been lucky enough to hunt in Utah and Colorado.
Big bulls sound all different kinds of ways, from high pitched tinny bugles to almost just grunts and growls, I do find that they sound meaner or angrier, when they are more dominant, but this isn't always 100% true just like humans I think they have different personalities, and some bulls just think they are bad asses. But I always seem to chase or want to chase the angrier bulls first as many times they are dominant, but not always the biggest racks just big mature big body bulls...most of the time.
What I mean by angry is that almost more pissed off sound like, like come on I will kick your ass, or I will breed you right now!! It is almost the most "confident" sounding bugle for lack of a better word, but they can be high or low, just like humans have different sounding voices, but you can tell when someone thinks they are the biggest and baddest. I also like to think of it as almost swearing in elk language, they know that if they talk like that there may be a fight but they don't care.
This is more right before they start gathering cows in Harems. It seems like after the big bulls get a harem they are'nt as pissed anymore and sound all kinds of ways.
I have been fooled more than a couple of times with my "theories" though
Tom C.