echoes

Echoes is the plural form of an echo, a sound that is reflected off a surface and returns to the listener after a delay. In acoustics, an audible echo requires sufficient distance between the sound source and the reflecting surface, and a surface that reflects sound without excessive absorption. The perceived time delay determines whether a sound is heard as a distinct echo or as reverberation; echoes can distort or clarify sound depending on context and design. Echoes are important in architectural acoustics, music production, and sonar, where they enable distance measurement and object detection.

In technology and biology, many organisms use echoes through echolocation; humans use ultrasonic echoes for sonar and medical imaging. In signal processing, an echo refers to a delayed version of a signal, and echo cancellation techniques are used to suppress unwanted echoes in communications.

In culture, Echoes has been used as a title in various works. The best-known musical use is Pink Floyd's 1971 instrumental Echoes from the album Meddle. More broadly, the term appears as titles for songs, albums, novels, and films, often conveying memory, repetition, or distant resonance.