What defines refraction in sound waves?

Refraction in sound waves is defined by the directional change of waves as they pass from one medium to another. This phenomenon occurs because sound waves travel at different speeds in different materials. When sound enters a new medium at an angle, the change in speed causes the wave to change direction. For example, when sound travels from air into water, the wave slows down and bends because of the different densities and elastic properties of the two mediums.

In contrast, the other options describe different acoustic phenomena. Changes in volume are related to the amplitude of the sound waves interacting with various materials rather than their directionality. Adjustments in pitch are due to variations in frequency, not a result of changing mediums. Reflection involves sound waves bouncing off surfaces, which is distinct from refraction, where the direction of the wave is altered as it passes through a boundary between materials. Thus, the definition of refraction is accurately captured by the answer focusing on the directional change of sound waves.