Your dog can communicate a number of different meanings, using just his bark. Different breeds of dogs have different vocal capabilities. This sonic diversity is linked both to behavior and the physiology of the dog’s vocal chords. Some dogs are so vocally diverse that they almost emulate singing - wavering between pitch and volume - and these barks can occur for a variety of reasons.
Dogs are pack animals and their ancestor the wolf still displays signs of this group mentality when communicating. A pack of wolves may howl in chorus to communicate to each other their location and to strengthen bonds. The same is true of neighborhood dogs. Once one dog starts a song, his bandmates along the street will join in. These howls are high-pitched and tremulous, swelling and receding in volume.
Some dogs actually are stimulated by music. They’ll howl along to the sound of their humans singing, or even playing the trumpet. This habit is their way of communicating with the pack. They hear the sound of what they believe to be another pack member howling, so they join in.
Pitch is an important factor in conveying meaning. As with musical instruments, the larger a surface, the deeper the pitch it generates. Dogs use this theory when deciding on what bark to use. They adopt a lower bark or growl to trick other animals that may hear them into thinking they’re larger than they really are. When a dog feels the need to make himself appear larger, it’s typically because he’s responding to a threat. A sustained, low-pitched bark, similar in style to how a rock singer might hold a note, conveys confidence and assertiveness in the face of a threat.
The basenji, an African hunting dog, has a distinctive yodel type call. It is unique to the breed, which is famous for not having a bark. This is because he is very closely related to his wild ancestors, who never evolved a bark and relied on howling and growling to communicate. The distinctive sound, called a baroo, is rather melodic and typically will cover a number of pitches, from mid-register to high.
When sight hounds, such as basset hounds, have cornered their quarry, they give a long, deep and mournful bay to signal to their master that they’ve got something. This type of singing is unique to sight hounds. Although it sounds mournful, the bay actually can be a sign of boredom if the dog is under-stimulated, or stimulation if the dog is in hunting or play mode.