Echo (phenomenon)
Encyclopedia
In audio signal processing
and acoustics
, an echo (plural echoes) is a reflection
of sound, arriving at the listener some time after the direct sound. 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
. The word echo derives from the Greek
ἠχώ (ēchō), itself from ἦχος (ēchos), "sound".
. An echo can be explained as a wave that has been reflected by a discontinuity in the propagation
medium
, and returns with sufficient magnitude and delay
to be perceived. Echoes are reflected off walls or hard surfaces like mountains and privacy fences.
When dealing with audible frequencies, the human ear cannot distinguish an echo from the original sound if the delay is less than 1/10 of a second. Thus, since the velocity of sound is approximately 343 m/s at a normal room temperature of about 20°C, the reflecting object must be more than 17.15 m from the sound source at this temperature for an echo to be heard by a person at the source.
Sound travels approximately 343 metres/s (1100 ft/s). If a sound produces an echo in 2 seconds, the object producing the echo would be half that distance away (the sound takes half the time to get to the object and half the time to return). The distance for an object with a 2-second echo return would be 1 sec X 343 metres/s or 343 metres (1100 ft). In most situations with human hearing, echoes are about one-half second or about half this distance, since sounds grow fainter with distance. In nature, canyon walls or rock cliffs facing water are the most common natural settings for hearing echoes.The strength of an echo is frequently measured in dB
sound pressure level SPL relative to the directly transmitted wave. Echoes may be desirable (as in sonar
) or undesirable (as in telephone
systems).
, an echo is the printing or display of characters (a) as they are entered from an input device, (b) as instructions are executed, or (c) as retransmitted characters received from a remote terminal
.
In computer graphics
, an echo is the immediate notification of the current values provided by an input device to the operator at the display console.
Some information from Federal Standard 1037C
and from MIL-STD-188
.
is a tape
delay
effect
, first made in 1959 that recreates the sound of an acoustic echo. Designed by Mike Battle, the Echoplex set a standard for the effect in the 1960s and was used by most of the notable guitar players of the era; original Echoplexes are highly sought after. While Echoplexes were used heavily by guitar players (and the occasional bass player, such as Chuck Rainey
, or trumpeter, such as Don Ellis
), many recording studio
s also used the Echoplex. Beginning in the 1970s, Market built the solid-state
Echoplex for Maestro. In the 2000s, most echo effects unit
s use electronic or digital circuitry to recreate the echo effect.
In Greek mythology
, Echo
(Greek: Ηχώ) was the personification of echo. According to Greek mythology Echo was a Nymph
who had the job of talking incessantly to Hera
, the Queen of the Gods, so that her husband, Zeus
, would not get caught in his numerous affairs. Hera caught on to Echo's trick and cursed her to only be able to say what others had just said — hence the word "echo".
in 2003 as part of the British Association's Festival of Science. It was also featured in one of the earlier episodes of the popular Discovery Channel television show MythBusters
. The actual reason for the myth is that a quack is a quiet and fading sound which produces faint echoes.
Audio signal processing
Audio signal processing, sometimes referred to as audio processing, is the intentional alteration of auditory signals, or sound. As audio signals may be electronically represented in either digital or analog format, signal processing may occur in either domain...
and acoustics
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...
, an echo (plural echoes) is a reflection
Reflection (physics)
Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...
of sound, arriving at the listener some time after the direct sound. 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
Speed of sound
The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at , the speed of sound is . This is , or about one kilometer in three seconds or approximately one mile in five seconds....
. The word echo derives from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
ἠχώ (ēchō), itself from ἦχος (ēchos), "sound".
Acoustic phenomenon
If so many reflections arrive at a listener that they are unable to distinguish between them, the proper term is reverberationReverberation
Reverberation is the persistence of sound in a particular space after the original sound is removed. A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air...
. An echo can be explained as a wave that has been reflected by a discontinuity in the propagation
Wave propagation
Wave propagation is any of the ways in which waves travel.With respect to the direction of the oscillation relative to the propagation direction, we can distinguish between longitudinal wave and transverse waves....
medium
Transmission medium
A transmission medium is a material substance that can propagate energy waves...
, and returns with sufficient magnitude and delay
Delay (audio effect)
Delay is an audio effect which records an input signal to an audio storage medium, and then plays it back after a period of time. The delayed signal may either be played back multiple times, or played back into the recording again, to create the sound of a repeating, decaying echo.-Early delay...
to be perceived. Echoes are reflected off walls or hard surfaces like mountains and privacy fences.
When dealing with audible frequencies, the human ear cannot distinguish an echo from the original sound if the delay is less than 1/10 of a second. Thus, since the velocity of sound is approximately 343 m/s at a normal room temperature of about 20°C, the reflecting object must be more than 17.15 m from the sound source at this temperature for an echo to be heard by a person at the source.
Sound travels approximately 343 metres/s (1100 ft/s). If a sound produces an echo in 2 seconds, the object producing the echo would be half that distance away (the sound takes half the time to get to the object and half the time to return). The distance for an object with a 2-second echo return would be 1 sec X 343 metres/s or 343 metres (1100 ft). In most situations with human hearing, echoes are about one-half second or about half this distance, since sounds grow fainter with distance. In nature, canyon walls or rock cliffs facing water are the most common natural settings for hearing echoes.The strength of an echo is frequently measured in dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
sound pressure level SPL relative to the directly transmitted wave. Echoes may be desirable (as in sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
) or undesirable (as in telephone
Telephone
The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...
systems).
In computing
In computingComputing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, an echo is the printing or display of characters (a) as they are entered from an input device, (b) as instructions are executed, or (c) as retransmitted characters received from a remote terminal
Computer terminal
A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system...
.
In computer graphics
Computer graphics
Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....
, an echo is the immediate notification of the current values provided by an input device to the operator at the display console.
Some information from Federal Standard 1037C
Federal Standard 1037C
Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended....
and from MIL-STD-188
MIL-STD-188
MIL-STD-188 is a series of U.S. military standards relating to telecommunications.-Purpose:Faced with “past technical deficiencies in telecommunications systems and equipment and software…that were traced to basic inadequacies in the application of telecommunication standards and to the lack of a...
.
In music
In music performance and recording, electric echo effects have been used since the 1950s. The EchoplexEchoplex
The Echoplex is a tape delay effect, first made in 1959. Designed by Mike Battle, the Echoplex set a standard for the effect in the 1960s and was used by some of the most notable guitar players of the era; original Echoplexes are highly sought after....
is a tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
delay
Delay (audio effect)
Delay is an audio effect which records an input signal to an audio storage medium, and then plays it back after a period of time. The delayed signal may either be played back multiple times, or played back into the recording again, to create the sound of a repeating, decaying echo.-Early delay...
effect
Sound effect
For the album by The Jam, see Sound Affects.Sound effects or audio effects are artificially created or enhanced sounds, or sound processes used to emphasize artistic or other content of films, television shows, live performance, animation, video games, music, or other media...
, first made in 1959 that recreates the sound of an acoustic echo. Designed by Mike Battle, the Echoplex set a standard for the effect in the 1960s and was used by most of the notable guitar players of the era; original Echoplexes are highly sought after. While Echoplexes were used heavily by guitar players (and the occasional bass player, such as Chuck Rainey
Chuck Rainey
Chuck Rainey, is an American bass guitar session musician, known for playing with many well-known American musicians and acts, including Donald Byrd, Steely Dan, Quincy Jones, and Aretha Franklin.-Biography:Rainey's youthful pursuits included violin, piano and trumpet...
, or trumpeter, such as Don Ellis
Don Ellis
Don Ellis was an American jazz trumpeter, drummer, composer and bandleader. He is best known for his extensive musical experimentation, particularly in the area of unusual time signatures...
), many recording studio
Recording studio
A recording studio is a facility for sound recording and mixing. Ideally both the recording and monitoring spaces are specially designed by an acoustician to achieve optimum acoustic properties...
s also used the Echoplex. Beginning in the 1970s, Market built the solid-state
Solid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
Echoplex for Maestro. In the 2000s, most echo effects unit
Effects unit
Effects units are electronic devices that alter how a musical instrument or other audio source sounds. Some effects subtly "color" a sound, while others transform it dramatically. Effects are used during live performances or in the studio, typically with electric guitar, keyboard and bass...
s use electronic or digital circuitry to recreate the echo effect.
Mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
, Echo
Echo (mythology)
In Greek mythology, Ekho , "echo", itself from ἦχος , "sound") was an Oread who loved her own voice. Zeus loved consorting with beautiful nymphs and visited them on Earth often. Eventually, Zeus's wife, Hera, became suspicious, and came from Mt...
(Greek: Ηχώ) was the personification of echo. According to Greek mythology Echo was a Nymph
Nymph
A nymph in Greek mythology is a female minor nature deity typically associated with a particular location or landform. Different from gods, nymphs are generally regarded as divine spirits who animate nature, and are usually depicted as beautiful, young nubile maidens who love to dance and sing;...
who had the job of talking incessantly to Hera
Hera
Hera was the wife and one of three sisters of Zeus in the Olympian pantheon of Greek mythology and religion. Her chief function was as the goddess of women and marriage. Her counterpart in the religion of ancient Rome was Juno. The cow and the peacock were sacred to her...
, the Queen of the Gods, so that her husband, Zeus
Zeus
In the ancient Greek religion, Zeus was the "Father of Gods and men" who ruled the Olympians of Mount Olympus as a father ruled the family. He was the god of sky and thunder in Greek mythology. His Roman counterpart is Jupiter and his Etruscan counterpart is Tinia.Zeus was the child of Cronus...
, would not get caught in his numerous affairs. Hera caught on to Echo's trick and cursed her to only be able to say what others had just said — hence the word "echo".
Duck's quack
"A duck's quack doesn't echo" is a much-quoted scientific myth. The truth is that a duck's quack does, in fact, echo; however, it may be difficult to hear. This myth was first debunked by the Acoustics Research Centre at the University of SalfordUniversity of Salford
The University of Salford is a campus university based in Salford, Greater Manchester, England with approximately 20,000 registered students. The main campus is about west of Manchester city centre, on the A6, opposite the former home of the physicist, James Prescott Joule and the Working Class...
in 2003 as part of the British Association's Festival of Science. It was also featured in one of the earlier episodes of the popular Discovery Channel television show MythBusters
MythBusters
MythBusters is a science entertainment TV program created and produced by Beyond Television Productions for the Discovery Channel. The series is screened by numerous international broadcasters, including Discovery Channel Australia, Discovery Channel Latin America, Discovery Channel Canada, Quest...
. The actual reason for the myth is that a quack is a quiet and fading sound which produces faint echoes.
Famous echoes
- Gol GumbazGol GumbazGol Gumbaz is the mausoleum of Mohammed Adil Shah, Sultan of Bijapur. The tomb, located in Bijapur, Karnataka in southern India, was completed in 1656 by the architect Yaqut of Dabul...
of BijapurBijapur, KarnatakaBijapur Urdu:بیجاپور city is the district headquarters of Bijapur District of Karnataka state. Bijapur city is well known for its historical monuments of architectural importance built during the rule of Adil Shahi dynasty...
, IndiaIndiaIndia , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
: Any whisper, clap or sound gets echoed repeatedly. - The GolkondaGolkondaGolkonda or Golla konda a ruined city of south-central India and capital of ancient Kingdom of Golkonda , is situated 11 km west of Hyderabad.The most important builder of Golkonda was a Hindu Kakatiya King...
Fort of Hyderabad, IndiaIndiaIndia , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world... - The Whispering GalleryWhispering galleryA whispering gallery is a gallery beneath a dome, vault, or enclosed in a circular or elliptical area in which whispers can be heard clearly in other parts of the building....
of St Paul's CathedralSt Paul's CathedralSt Paul's Cathedral, London, is a Church of England cathedral and seat of the Bishop of London. Its dedication to Paul the Apostle dates back to the original church on this site, founded in AD 604. St Paul's sits at the top of Ludgate Hill, the highest point in the City of London, and is the mother...
, LondonLondonLondon is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...
, England - Echo Point, the Three SistersThree Sisters (Australia)The Three Sisters is a rock formation in the Blue Mountains of New South Wales, Australia. They are close to the town of Katoomba and are one of the Blue Mountains' best known sites, towering above the Jamison Valley. Their names are Meehni , Wimlah , and Gunnedoo .-Geology:The Sisters were formed...
, Katoomba, AustraliaAustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area... - The Temple of Kukulcan ("El Castillo"), Chichen ItzaChichen ItzaChichen Itza is a large pre-Columbian archaeological site built by the Maya civilization located in the northern center of the Yucatán Peninsula, in the Municipality of Tinúm, Yucatán state, present-day Mexico....
, MexicoMexicoThe United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of... - The Baptistry of Pisa, PisaPisaPisa is a city in Tuscany, Central Italy, on the right bank of the mouth of the River Arno on the Tyrrhenian Sea. It is the capital city of the Province of Pisa...
, ItalyItalyItaly , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and... - The echo near MilanMilanMilan is the second-largest city in Italy and the capital city of the region of Lombardy and of the province of Milan. The city proper has a population of about 1.3 million, while its urban area, roughly coinciding with its administrative province and the bordering Province of Monza and Brianza ,...
visited by Mark TwainMark TwainSamuel Langhorne Clemens , better known by his pen name Mark Twain, was an American author and humorist...
in The Innocents Abroad - The echo in ChinonChinonChinon is a commune in the Indre-et-Loire department in central France well known for Château de Chinon.In the Middle Ages, Chinon developed especially during the reign of Henry II . The castle was rebuilt and extended, becoming one of his favorite residences...
which is used in a traditional local rhyme.