Sounds travel faster in water. Their speed in water is five times of their speed in air.
With such high speed, sound waves instead of going through ossicles bones (in the inner ears) directly vibrate the heavy bone behind the ears. Due to this reason, a person below water hears sound waves of higher frequency.
However, while travelling through air sound waves reaches at lower frequency
Waves of sound have different properties, among them amplitude is the one that determines the loudness or volume of the sound. The amplitude is the height of the wave, measured in meters, or in other word the maximum displacement of the sound's particle from its position of equilibrium. If a dolphin calling sounds louder because of the background noise, the waves of the sound that the dolphin produces would have a higher amplitude.
