When scientists study dog sounds, they identify a number of different vocalizations with different nuances of meaning. There are two important factors to attend to in dog vocalizations. The first is the pitch of the sound. For barks and other sounds, low-pitched sounds usually indicate threats, anger, and the possibility of aggression, while higher-pitched sounds can mean fear or pain or, where they are less sharp, pleasure or playfulness.
The second factor in dog vocalizations is the frequency or repetition rate of the sound. Sounds that are repeated often, at a fast rate, indicate a degree of excitement and urgency. Sounds that are spaced out or not repeated usually indicate a lower level of excitement or a passing state of mind.
In addition, the duration of the sounds is also important. High-pitched sounds of short duration frequently indicate fear or pain. On the other hand, the same sounds repeated at a slower rate indicate playfulness or anticipation of pleasure. Generally speaking, more sustained sounds indicate intentionality, behavior that is about to happen, such as the low-pitched, sustained growl that precedes an attack.