Echo (redirected from metallic echo)

Echo, in Greek mythology

Echo, in Greek mythology, mountain nymph. She assisted Zeus in one of his amorous adventures by distracting Hera with her chatter. For this Hera made her unable to speak except to repeat another's last words. She fell in love with Narcissus, but when he rejected her, she pined away until only her voice remained. In another myth, she was loved by Pan, who, because he could not win her, caused shepherds to tear her asunder; Gaea buried her limbs, leaving only her voice.

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echo, in acoustics

echo, reflection of a sound wave back to its source in sufficient strength and with a sufficient time lag to be separately distinguished. If a sound wave returns within 1-10 sec, the human ear is incapable of distinguishing it from the orginal one. Thus, since the velocity of sound is c.344 m (1,130 ft) per sec at a normal room temperature of about 20°C; (68°F;), a reflecting wall must be more than 16.2 m (56 1-2 ft) from the sound source at this temperature for an echo to be heard by a person at the source. In this case the sound requires 1-20 sec to reach the reflecting surface and the same time to return. Bats navigate by listening for the echo of their high-frequency cry. Sonar and depth sounders work by analyzing electronically the echo time lag of sound waves, generally between 10 and 50 kilohertz, produced by underwater transducers. Radar sets broadcast radio waves, usually between 100 and 10,000 megahertz, pick up the portion reflected back by objects, and electronically determine the distance and direction of the objects. A sound echo that is reflected again and again from different surfaces, as by parallel walls in a tunnel, is called reverberation. When a surface reflects sound it partially absorbs and partially reflects the energy. As the process is repeated the sound becomes weaker and weaker and eventually ceases.

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Echo

In Greek mythology, a mountain nymph transformed into a disembodied voice. According to Ovid, her chatter distracted Hera from the infidelities of Zeus, and the goddess punished her by depriving her of independent speech, rendering her able only to repeat the last words spoken by another. When Narcissus failed to requite her love, she faded away into a voice only.

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(1) A repetition of a signal in a communications line. The difference in electrical characteristics at opposite ends can cause the echo.

(2) In communications, to transmit received data back to the sending station allowing the user to inspect visually what was received. A local echo displays what you type on your screen.

(3) A DOS and OS/2 screen command that displays messages and turns off/on screen responses. See DOS batch file.

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Echo

pined for Narcissus till only voice remained. [Gk. Myth.: Brewer Dictionary, 363; Br. Lit.: Comus, in Benét, 217]

See : Love, Unrequited

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Echo

beautiful nymph who, by her constant talk, kept Hera away from Zeus. [Gk. Myth.: Howe, 89]

See : Talkativeness

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1.		echo - A topic group on FidoNet's echomail system. Compare newsgroup.
2.		echo - A Unix command that just prints its arguments.