An echo is a reflection of a sound that takes longer to arrive at the listener than the direct arrival of the sound from the source. This effect can also be emulated mechanically or digitally.

Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single reflection of the sound source. The time delay is the extra distance divided by the speed of sound.

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