The Question: So, in my fantasy world, I have a race of human-like creatures that can talk to any land animal. The basic question is what kind of and how many voice boxes would this race need to be able to communicate with almost any animal?
Some background: In my fantasy world seven races were created. The first race created was of very human-like creatures who were given something I call the "Word Law." Basically, it's my version of magic, but the best way to understand it that it is like the run-time script of my fantasy universe--that is, simply by speaking something in the language that goes with it, "First Word," one can actually change the physical state of something.
Anyway, 100 years later half of this first race had fallen into darkness, so six new races were created as 'protectors.' The job of the protector races was to keep the Firstlings, as the first race is called, from spoiling their world. The 2nd race was to protect the mountains and their treasures, the 3rd was to protect plains and their bounty, the 4th was to protect the forests and their secrets, the 5th was to protect the caverns and the the Deep (a series of cassavas chasms running throughout this world), the 6th was to protect the air-breathing animals (mammals, birds, reptiles, insects), and the 7th the water-breathing ones (fish, etc.).
Now, one of the interesting features of race #6, the 'Beastguard' as I have called them, is that they were given an instinctive ability to communicate with animals. A note on the animals in this world is that while they do indeed communicate with pheromones and body language, they all have a primitive form of audible language themselves. Some animals are smarter than others (with a loose relation of a given animal's intelligence attached to its size and class [mammal, reptile, ...]) and have a more expressive language than others, but they all have one. Infact, some of these animals have had their intelligence enhanced and been given the ability to speak the common tongue (which is not Firstword) by users of the Wordlaw, but most have not.
THE BIG PROBLEM That said, I would like to have a biological grasp of what vocal hardware these Beastguard would need. I could just pull a hand-wave and say, "they can because they can," or, "I've a version of magic so this works," but I would rather have a biological explanation. For instance, we humans have single voice box with a limited frequency production and resonance range. While the animals in this world aren't exactly the same as the ones in ours, they are similar, and the animals in our world have vocal ranges that are all over the place. Birds even have more than one voice box. So, to be able to reproduce the sounds made by most all animals, what vocal equipment would my Beastguard need?
Feel free to get as technical as you want with the answer, I'll probably give a symplified version to my readers, but I want something believable. Thanks!