Sounds thought of as harsh are combinations of tones that do not harmonize. If the raucous call of a bluejay were analyzed, it would be found to be a combination of extremely discordant notes. All noises are miscellaneous combinations of tones, unpleasant because they are unrelated. Like light waves, sound waves can be reflected and focused. A flat surface, like that of a cliff or wall, reflects sound better than an irregular surface, which tends to break up sound waves.
Echoes are useful in many ways.
In a fog, a ship's captain can often tell whether he is near a hilly shoreline by listening for echoes of the ship's whistle. Underwater sonar equipment uses echoes of a supersonic signal similarly to detect submarines. Depth finders use echoes from the ocean bottom to measure the depth of the water. A band shell focuses the sound of the band in just the same way an automobile headlight reflector focuses light. The headlight reflector and many band shells are in the shape of a parabolic curve.