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Studio monitor
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This article is about studio reference loudspeakers. For onstage monitor speakers for live performances, see foldback (sound engineering).
Not to be confused with Broadcast reference monitor.
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PreSonus Eris E4.5 HD Active Studio Monitor.
Studio monitors are loudspeakers in speaker enclosures specifically designed for professional audio production applications, such as recording studios, filmmaking, television studios, radio studios and project or home studios, where accurate audio reproduction is crucial. Among audio engineers, the term monitor implies that the speaker is designed to produce relatively flat (linear) phase and frequency responses. In other words, it exhibits minimal emphasis or de-emphasis of particular frequencies, the loudspeaker gives an accurate reproduction of the tonal qualities of the source audio ("uncolored" or "transparent" are synonyms), and there will be no relative phase shift of particular frequencies—meaning no distortion in sound-stage perspective for stereo recordings.
Beyond stereo sound-stage requirements, a linear phase response helps impulse response remain true to source without encountering "smearing". An unqualified reference to a monitor often refers to a near-field (compact or close-field) design. This is a speaker small enough to sit on a stand or desk in proximity to the listener, so that most of the sound that the listener hears is coming directly from the speaker, rather than reflecting off of walls and ceilings (and thus picking up coloration and reverberation from the room). Monitor speakers may include more than one type of driver (e.g., a tweeter and a woofer) or, for monitoring low-frequency sounds, such as bass drum, single-driver subwoofer cabinets may be used.
Also, studio monitors are made in a more physically robust manner than home hi-fi loudspeakers; whereas home hi-fi loudspeakers often only have to reproduce compressed commercial recordings, studio monitors have to cope with the high volumes and sudden sound bursts that may happen in the studio when playing back unmastered mixes.
Contents
[hide]
1 Uses
2 History
2.1 1920s and 1930s
2.2 1940s and 1950s
2.3 1960s and 1970s
2.4 1980s-1990s
2.5 2000s
3 Comparison with hi-fi speakers
4 See also
5 References
Uses[edit]
Quested HM412 main monitor, Studio 9000, PatchWerk Recording Studios
Broadcasting and recording organisations employ audio engineers who use loudspeakers to assess the aesthetic merits of the programme and to tailor the balance by audio mixing and mastering to achieve the desired end result. Loudspeakers are also required at various points in the chain to enable engineers to ensure that the programme is reasonably free from technical defects, such as audible distortion or background noise.[1]
The engineer may mix programming that will sound pleasing on the widest range of playback systems used by regular listeners (i.e. high-end audio, low-quality radios in clock radios and "boom boxes", in club PA systems, in a car stereo or a home stereo). While some broadcasters like the BBC generally believe in using monitors of "the highest practicable standard of performance",[citation needed] some audio engineers argue that monitoring should be carried out with loudspeakers of mediocre technical quality to be representative of the regular systems end-users are likely to be listening with; or that some technical defects are apparent only with high-grade reproducing equipment and therefore can be ignored.[1] However, as a public broadcaster dealing with a lot of live material, the BBC's criteria for studio monitors view is that they should be "as free as possible from avoidable defects". It is argued that real life low-grade sound systems are so different that it would be impossible to compensate for the characteristics of every type of system available; technical faults must not be apparent to even a minority of listeners while remaining undetected by the operating staff. It is further argued that, because of technical progress in the science of sound transmission, equipment in the studio originating the programme should have a higher standard of performance than the equipment employed in reproducing it, since the former has a longer life.[1]
In fact, most professional audio production studios have several sets of monitors spanning the range of playback systems in the market. This may include a sampling of large, expensive speakers as may be used in movie theatres, hi-fi style speakers, car speakers, portable music systems, PC speakers and consumer-grade headphones.[citation needed]
Amplification: Studio monitors may be "active" (including one or more internal power amplifier(s)), or passive (these require an external power amplifier). Active models are usually bi-amplified, which means that the input sound signal is divided into two parts by an active crossover for low and high frequency components. Both parts are amplified using separate low- and high-frequency amplifiers, and then the low-frequency part is routed to a woofer and the high-frequency part is routed to a tweeter or horn. Bi-amplification is done so that a cleaner overall sound reproduction can be obtained, since signals are easier to process before power amplification. Consumer loudspeakers may or may not have these various design goals.
History[edit]
1920s and 1930s[edit]
In the early years of the recording industry in the 1920s and 1930s, studio monitors were used primarily to check for noise interference and obvious technical problems rather than for making artistic evaluations of the performance and recording. Musicians were recorded live and the producer judged the performance on this basis, relying on simple tried-and-true microphone techniques to ensure that it had been adequately captured; playback through monitors was used simply to check that no obvious technical flaws had spoiled the original recording.
As a result, early monitors tended to be basic loudspeaker cabinets. The state-of-the-art loudspeakers of the era were massive horn-loaded systems which were mostly used in cinemas. High-end loudspeaker design grew out of the demands of the motion picture industry and most of the early loudspeaker pioneers worked in Los Angeles where they attempted to solve the problems of cinema sound. Stereophonic sound was in its infancy, having been pioneered in Britain by an engineer who worked for EMI. Designing monitors for recording studios was not a major priority.
1940s and 1950s[edit]
The first high-quality loudspeaker developed expressly as a studio monitor was the Altec Lansing Duplex 604 in 1944. This innovative driver has historically been regarded as growing out of the work of James Bullough Lansing who had previously supplied the drivers for the Shearer Horn in 1936, a speaker that had rapidly become the industry standard in motion-picture sound. He had also designed the smaller Iconic and this was widely employed at the time as a motion-picture studio monitor. The 604 was a relatively compact coaxial design and within a few years it became the industry standard in the United States, a position it maintained in its various incarnations (the 604 went through eleven model-changes) over the next 25 years. It was common in US studios throughout the 1950s and 60s and remained in continuous production until 1998.
Siemens Recording Studio ca. 1956 as seen in the Deutsches Museum in Munich Germany.
In the UK, Tannoy introduced its own coaxial design, the Dual Concentric, and this assumed the same reference role in Europe as the Altec 604 held in the US. The British Broadcasting Corporation researchers conducted evaluations on as many speakers as they could obtain in around 1948, but found commercial loudspeaker makers had little to offer that met their requirements. The BBC needed speakers that worked well with program material within real professional and domestic settings environments, and not just fulfil technical measurements such as frequency-response, distortion, monitors in anechoic chambers. Above all, the BBC required monitors to sound balanced, be neutral in tone, and lack colouration.[2] Monitor usage in the industry was highly conservative, with almost monopolistic reliance on industry “standards”, in spite of the sonic failings of these aging designs. The Altec 604 had a notoriously ragged frequency response but almost all U.S studios continued to use it because virtually every producer and engineer knew its sound intimately and were practiced at listening through its sonic limitations.
Recording through unfamiliar monitors, no matter how technically advanced, was hazardous because engineers unfamiliar with their sonic signatures could make poor production decisions and it was financially unviable to give production staff expensive studio time to familiarize themselves with new monitors. As a result, pretty well every U.S studio had a set of 604’s and every European studio a Tannoy Dual Concentric or two. However, in 1959, at the height of its industry dominance, Altec made the mistake of replacing the 604 with the 605A Duplex, a design widely regarded as inferior to its predecessor. There was a backlash from some record companies and studios and this allowed Altec’s competitor, JBL (a company originally started by 604 designer James B. Lansing), to make inroads into the pro monitor market.
Capitol Records replaced their Altecs with JBL D50 Monitors and a few years later their UK affiliate, EMI, also made the move to JBL’s. Although Altec re-introduced the 604 as the "E" version Super Duplex in response to the criticism, they now had a major industry rival to contend with. Over the next decade most of the developments in studio monitor design originated from JBL.
As the public broadcaster in the UK, the BBC had the determinant role in defining industry standards. Its renowned research departments invested considerable resources in determining studio monitor suited to their different broadcasting needs, and also created their own models from first principles. A 1958 research paper identified the sound goal, in a monaural system:
It is assumed that the ideal to be aimed at in the design of a sound reproducing system is realism, i.e. that the listener should be able to imagine himself to be in the presence of the original source of sound. There is, of course, scope for legitimate experiment in the processing of the reproduced signals in an endeavour to improve on nature, however, realism, or as near an approach to it as may be possible, ought surely to be regarded as the normal condition and avoidable departures from this state, while justified upon occasion, should not be allowed to become a permanent feature of the system.[1]
In designing a loudspeaker, the BBC established the compromise that had to be established between size, weight and cost considerations. Two-way designs were preferred due to the inherently simpler crossover network, but were subject to the limitations of speaker driver technology at the time – there were few high-frequency units available at the time that functioned down to 1.5 kHz, meaning that the woofer must operate in a predictable manner up to about 2 kHz.[3] The BBC developed a two-way studio monitor in 1959, the LS5/1, using a 58mm Celestion tweeter and 380mm Goodmans bass unit, but continually had problems with consistency of the bass units. The successful testing of a 305mm bass cone made with new thermoplastics led to development and deployment of the LS5/5 and LS5/6 monitors that occupied only 60% volume of its predecessor.[3]
As recording became less and less “live” and multi-tracking and overdubbing became the norm, the studio monitor became far more crucial to the recording process. When there was no original performance outside what existed on the tape, the monitor became the touchstone of all engineering and production decisions. As a result, accuracy and transparency became paramount and the conservatism evident in the retention of the 604 as the standard for over twenty years began to give way to fresh technological development. Despite this, the 604 continued to be widely used - mainly because many engineers and producers were so familiar with their sonic signature that they were reluctant to change.
1960s and 1970s[edit]
In a BBC white paper published in January 1963, the authors explored two-channel stereophony, and remarked that it was at a disadvantage compared with multi-channel stereophony that was already available in cinemas in that "the full intended effects is apparent only to observers located within in a restricted area in front of the loudspeakers". The authors expressed reservations about dispersion and directionality in 2-channel systems, noting that the "face-to-face listening arrangement" was not able to give an acceptable presentation for a centrally-located observer in a domestic setting.[4] The paper concluded:
The achievement of suitable directional characteristics within the aesthetic and economic limitations applying to domestic equipment will however require a much greater research effort than either the corporation or the radio industry have so far been able to devote to the subject.[4]
To complement its larger two-way monitors for studio use, the BBC developed a small speaker for near-field monitoring of the frequency range from 400 Hz to about 20 kHz for its outside broadcasting monitoring. The principal constraints were space and situations where using headphones is unsatisfactory, such as in mobile broadcasting vans. Based on scaling tests done in 1968, and detailed audio work against the LS5/8 – a large "Grade I monitor" already in use at the time – and with live sources, the BBC Research Department developed the LS3/5, which became the famous LS3/5A that was used from 1975 to much of the 1990s and beyond by the BBC and audiophiles alike.[5][6][7]
In the late 1960s JBL introduced two monitors which helped secure them pre-eminence in the industry. The 4320 was a direct competitor to the Altec 604 but was a more accurate and powerful speaker and it quickly made inroads against the industry standard. However, it was the more compact 4310 that revolutionized monitoring by introducing the idea of close or "nearfield" monitoring. (The sound field very close to a sound source is called the "near-field." By "very close" is meant in the predominantly direct, rather than reflected, sound field. A near-field speaker is a compact studio monitor designed for listening at close distances (3 to 5 feet (0.9 to 1.5 m)), so, in theory, the effects of poor room acoustics are greatly reduced.)
The 4310 was small enough to be placed on the recording console and listened to from much closer distances than the traditional large wall-(or "soffit") mounted main monitors. As a result, studio-acoustic problems were minimized. Smaller studios found the 4310 ideal and that monitor and its successor, the 4311, became studio fixtures throughout the 1970s. Ironically, the 4310 had been designed to replicate the sonic idiosyncrasies of the Altec 604 but in a smaller package to cater for the technical needs of the time.
The 4311 was so popular with professionals that JBL introduced a domestic version for the burgeoning home-audio market. This speaker, the JBL L-100, (or "Century") was a massive success and became the biggest-selling hi-fi speaker ever within a few years. By 1975, JBL overtook Altec as the monitor of choice for most studios. The major studios continued to use huge designs mounted on the wall which were able to produce prodigious SPL's and amounts of bass.
This trend reached its zenith with The Who's use of a dozen JBL 4350 monitors, each capable of 125 dB and containing two fifteen-inch woofers and a twelve-inch mid-bass driver. Most studios, however, also used more modest monitoring devices to check how recordings would sound through car speakers and cheap home systems. A favourite "grot-box" monitor employed in this way was the Auratone 5C, a crude single-driver device that gave a reasonable facsimile of typical lo-fi sound.
However, a backlash against the behemoth monitor was soon to take place. With the advent of punk, new wave, indie, and lo-fi, a reaction to high-tech recording and large corporate-style studios set in and do-it-yourself recording methods became the vogue. Smaller, less expensive, recording studios needed smaller, less expensive monitors and the Yamaha NS-10, a design introduced in 1978 ironically for the home audio market, became the monitor of choice for many studios in the 1980s.[8] While its sound-quality has often been derided, even by those who monitor through it, the NS-10 continues in use to this day and many more successful recordings have been produced with its aid over the past twenty five years than with any other monitor.[9][10]
1980s-1990s[edit]
Tannoy, Dynaudio, Genelec, and K+H studio monitors.
By the mid-1980s the near-field monitor had become a permanent fixture. The larger studios still had large soffit-mounted main monitors but producers and engineers spent most of their time working with near-fields. Common large monitors of the time were Eastlake / Westlake monitors with twin 15" bass units, a wooden midrange horn and a horn-loaded tweeter. The UREI 813 was also popular. Based on the almost ageless Altec 604 with a Time-Align passive crossover network developed by Ed Long, it included delay circuitry to align the acoustic centers of the low and high-frequency components. Fostex "Laboratory Series" monitors were used in a few high-end studios, but with increasing costs of manufacture, they became rare. The once dominant JBL fell gradually into disfavour.
One of the most striking trends was the growth of soft-dome monitors. These operated without horn-loaded drivers. Horns, while having advantages in transient response and efficiency, tend to be hard to listen to over long periods. The lack of distortion of high-end dome midrange & tweeters made them easy to work with all day (and night). Typical soft-dome systems were made by Roger Quested, ATC, Neil Grant and PMC and were actively driven by racks of active crossovers and amplifiers. Other monitor and studio designers like Tom Hidley, Phil Newall and Sam Toyoshima continued research into the speaker/room interface and led developments in room design, trapping, absorption and diffusion to create a consistent and neutral monitoring environment.
2000s[edit]
Bruce Gil in a mastering studio (a near-field studio monitor can be seen on the left.
The main post-NS-10 trend has been the almost universal acceptance of powered monitors where the speaker enclosure contains the driving amplifiers. Passive monitors require outboard power amplifiers to drive them as well as speaker wire to connect them. Powered monitors, by contrast, are comparatively more convenient and streamlined single units, which in addition, marketeers claim a number of technical advantages. The interface between speaker and amplifier can be optimized, possibly offering greater control and precision, and advances in amplifier design have reduced the size and weight of the electronics significantly. The result has been that passive monitors have become far less common than powered monitors in project and home studios.
In the 2000s, there was a trend to focus on "translation". Engineers tended to choose monitors less for their accuracy than for their ability to “translate” – to make recordings sound good on a variety of playback systems, from stock car radios and standard boom boxes to esoteric audiophile systems. As the mix engineer Chris Lord-Alge has noted:
Ninety-five percent of people listen to music in their car or on a cheap home stereo; 5 percent may have better systems; and maybe 1 percent have a $20,000 stereo. So if it doesn’t sound good on something small, what’s the point? You can mix in front of these huge, beautiful, pristine, $10,000 powered monitors all you want. But no one else has these monitors, so you’re more likely to end up with a translation problem.”[11]
But it is uncertain just tools what aid translation. Some producers argue that accuracy is still the best guarantee. If a producer or audio engineer is listening to recorded tracks and mixing tracks using a "flattering" monitor speaker, she may miss subtle problems in the mic'ing or recording quality that a more precise monitor would expose. Other producers feel that monitors should mimic home audio and car speakers, as this is what most consumers listen to music on. Still more believe that monitors need to be relentlessly unflattering, so that the producer and engineer must work hard to make recordings sound good.
Comparison with hi-fi speakers[edit]
Late model (c.1998) BBC LS3/5A manufactured under license by Spendor
No speaker, monitor or hi-fi sound system, regardless of the design principle or cost, has a completely flat frequency response; all speakers color the sound to some degree. Monitor speakers are assumed to be as free as possible from coloration. While no rigid distinction exists between consumer speakers and studio monitors, manufacturers more and more accent the difference in their marketing material. Generally, studio monitors are physically robust, to cope with the high volumes and physical knocks that may happen in the studio, and are used for listening at shorter distances (e.g., near field) than hi-fi speakers, though nothing precludes them from being used in a home-sized environment. In one prominent recording magazine, Sound on Sound, the number of self-amplified (active) studio monitor reviews significantly outweighs the number of passive monitor reviews over the past two decades indicating that studio monitors are predominantly self-amplified, although not exclusively so.[12] Hi-fi speakers usually require external amplification.[citation needed]
Monitors are used by almost all professional producers and audio engineers. The advantage of studio monitors is that the production translates better to other sound systems.[13] In the 1970s, the JBL 4311’s domestic equivalent, the L-100, was used in a large number of homes, while the Yamaha NS-10 served both domestically and professionally during the 1980s. Despite not being a "commercial product" at the outset, the BBC licensed production of the LS3/5A monitor, which it used internally. It was commercially successful in its twenty-something-year life,[7][14] from 1975 until approximately 1998. The diminutive BBC speaker has amassed an "enthusiastic, focused, and … loyal following", according to Paul Seydor in The Absolute Sound.[15] Estimates of their sales differ, but are generally in the 100,000 pairs ballpark.[15][16]
Professional audio companies such as Genelec, Neumann (formerly Klein + Hummel), Quested, and M & K sell almost exclusively to recording studios and record producers, who comprise key players in the professional monitor market. Most of the consumer audio manufacturers confine themselves to supplying speakers for home hi-fi systems. Companies that straddle both worlds, like Tannoy, ADAM, PMC, Focal/JM Labs, surrounTec, Dynaudio, and JBL, tend to clearly differentiate their monitor and hi-fi lines.
See also[edit]
Loudspeaker acoustics
List of loudspeaker manufacturers
Digital room correction
Room acoustics
References[edit]
^ Jump up to: a b c d "The Development of High-Quality Monitoring Loudspeakers: A Review of Progress" (Expanded Version of I.EoE. Paper Read on 23rd April 1958). Report No. L-041 (1958/31), The British Broadcasting Corporation
Jump up ^ Seydor, Paul. "The BBC Monitor". The Absolute Sound’s Illustrated History of High-End Audio p.306
^ Jump up to: a b "The Design of the Studio Monitoring Loudspeakers Types LS5/5 and LS5/6". Report No. PH13 (1967/57), November 1967, The British Broadcasting Corporation
^ Jump up to: a b "The Influence of Loudspeaker Directivity and Orientation on the Effective Audience Area in Two-Channel Stereophonic Reproduction", BBC Engineering Division, January 1963.
Jump up ^ Prakel, David (August 1979). "BBC's Home Service", Hi-Fi Answers, pp67–9 (Courtesy link)
Jump up ^ H.D. Harwood, BSc, M.E. Whatton, C.Eng., M.I.E.E. and R.W. Mills. (October 1976) "The design of the miniature monitoring loudspeaker type LS3/5A", Research Department, Engineering Division, The British Broadcasting Corporation
^ Jump up to: a b Atkinson, John (April 2007). "Stirling LS3/5a V2, 2007". Stereophile (Vol.30 No.4).
Jump up ^ Phil Ward, "The Yamaha NS10 Story". Sound on Sound, September 2008
Jump up ^ Gardiner, Bryan (15 September 2010). "Yamaha's NS-10: The Most Important Speaker You've Never Heard Of". Gizmodo
Jump up ^ PR Newell, KR Holland & JP Newell. "The Yamaha NS10M: Twenty Years a Reference Monitor. Why?". report commissioned by Sound on Sound
Jump up ^ Knave, Brian (June 1, 2001) "Good References", emusician.
Jump up ^ "review search term "Monitor"". Sound On Sound. 1994–2016.
Jump up ^ http://www.topstudiogear.com/difference-between-monitors-and-speakers/
Jump up ^ "A timeline of LS3/5A manufacture". Ls351.com
^ Jump up to: a b Seydor, Paul (2 December 2008). "Stirling Broadcast LS3/5a V2 Loudspeaker". The Absolute Sound.
Jump up ^ Kessler, Ken (June 2001) "LS3/5A Shootout". HiFi News (courtesy link to reproduced content)
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text:
Caribbean Plate
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Caribbean Plate
Type
Minor
Approximate area
3,300,000 km2[1]
Movement1
north-west
Speed1
10-11mm/year
Features
Central America, Cuba, Hispaniola. Caribbean Sea
1Relative to the African Plate
Volcanoes of the Caribbean.
The Caribbean Plate is a mostly oceanic tectonic plate underlying Central America and the Caribbean Sea off the north coast of South America.
Roughly 3.2 million square kilometers (1.2 million square miles) in area, the Caribbean Plate borders the North American Plate, the South American Plate, the Nazca Plate and the Cocos Plate. These borders are regions of intense seismic activity, including frequent earthquakes, occasional tsunamis,[2] and volcanic eruptions.
Contents
[hide]
1 Boundary types
2 Origin
3 First American land bridge
4 Great American Interchange
5 See also
6 References
7 External links
Boundary types[edit]
The northern boundary with the North American plate is a transform or strike-slip boundary which runs from the border area of Belize, Guatemala (Motagua Fault), and Honduras in Central America, eastward through the Cayman trough on south of the southeast coast of Cuba, and just north of Hispaniola, Puerto Rico, and the Virgin Islands. Part of the Puerto Rico Trench, the deepest part of the Atlantic Ocean (roughly 8,400 meters), lies along this border. The Puerto Rico trench is at a complex transition from the subduction boundary to the south and the transform boundary to the west.
The eastern boundary is a subduction zone, the Lesser Antilles subduction zone, where oceanic crust of the South American Plate is being subducted under the Caribbean Plate. Subduction forms the volcanic islands of the Lesser Antilles Volcanic Arc from the Virgin Islands in the north to the islands off the coast of Venezuela in the south. This boundary contains seventeen active volcanoes, most notably Soufriere Hills on Montserrat; Mount Pelée on Martinique; La Grande Soufrière on Guadeloupe; Soufrière Saint Vincent on Saint Vincent; and the submarine volcano Kick 'em Jenny which lies about 10 km north of Grenada. Large historical earthquakes in 1839 and 1843 in this region are possibly megathrust earthquakes.[3][4]
Along the geologically complex southern boundary,[5] the Caribbean Plate interacts with the South American Plate forming Barbados, Trinidad and Tobago (all on the Caribbean Plate), and islands off the coast of Venezuela (including the Leeward Antilles) and Colombia. This boundary is in part the result of transform faulting along with thrust faulting and some subduction. The rich Venezuelan petroleum fields possibly result from this complex plate interaction. The Caribbean plate is moving eastward about 22 millimeters per year in relation to the South American plate.[6][7] In Venezuela much of the movement between the Caribbean Plate and the South American plate occurs along the faults of Boconó, El Pilar and San Sebastián.[5]
The western portion of the plate is occupied by Central America. The Cocos Plate in the Pacific Ocean is subducted beneath the Caribbean Plate, just off the western coast of Central America. This subduction forms the volcanoes of Guatemala, El Salvador, Nicaragua, and Costa Rica, also known as the Central America Volcanic Arc.
Origin[edit]
The usual theory as to the origin of the Caribbean Plate was confronted by a contrasting theory in 2002.
The mainstream theory holds that it is the Caribbean large igneous province (CLIP) which formed in the Pacific Ocean tens of millions of years ago. As the Atlantic Ocean widened, North America and South America were pushed westward, separated for a time by oceanic crust.[8] The Pacific Ocean floor subducted under this oceanic crust between the continents. The CLIP drifted into the same area, but as it was less dense and thicker than the surrounding oceanic crust, it did not subduct, but rather overrode the ocean floor, continuing to move eastward relative to North America and South America. With the formation of the Isthmus of Panama 3 million years ago, it ultimately lost its connection to the Pacific.
The more recent theory asserts that the Caribbean Plate came into being from an Atlantic hotspot which no longer exists. This theory points to evidence of the absolute motion of the Caribbean Plate which indicates that it moves westward, not east, and that its apparent eastward motion is only relative to the motions of the North American Plate and the South American Plate.[9]
First American land bridge[edit]
The Caribbean Plate began its eastward migration 80 million years ago (Ma) during the Late Cretaceous. This migration eventually resulted in a volcanic arc stretching from north-western South America to the Yucatán Peninsula, today represented by the Aves Islands and the Lesser and Greater Antilles. This arc was the subject of constant tectonism and sea-level fluctuations but lasted until the mid-Eocene and intermittently formed a land bridge along the eastern and northern boundaries of the Caribbean Plate.[10] (What would eventually become present-day Central America, part of the western plate boundary, was still isolated in the Pacific.)
58.5 to 56.5 Ma, during the Late Paleocene, a local sea-level low-stand assisted by the continental uplift of the western margin of South America, resulted in a fully operative land bridge over which several groups of mammals apparently took part in an interchange. For example, xenarthrans are known from the Itaboraian stage of the South American Land Mammal Age (SALMA) (59–57 Ma), palaeanodonts from the Tiffanian North American Land Mammal Age (NALMA) (57 Ma) and Eurotamandua from the early middle Eocene (50 Ma) of Europe; opossums are known from the Tiupampan/Itaboraian SALMA (64–57 Ma), from the Clarkforkian NALMA (55 Ma); and from the Ypresian in Europe (55 Ma).[10]
See also: Aves Ridge
Great American Interchange[edit]
The Great American Interchange in which land and freshwater fauna migrated between North America and South America via the uplifted western margin of the Caribbean Plate (Central America) was a later event, which peaked dramatically around three million years (Ma) ago during the Piacenzian age.
See also[edit]
2010 Haiti earthquake
Central America Volcanic Arc
Gonâve Microplate
List of earthquakes in Guatemala
List of tectonic plates
Panama Plate
References[edit]
Jump up ^ "Sizes of Tectonic or Lithospheric Plates". About.com Geology.
Jump up ^ Fernández-Arce, Mario; Alvarado-Delgado, Guillermo (December 2005). "Tsunamis and Tsunami Preparedness in Costa Rica, Central America" (PDF). ISET Journal of Earthquake Technology. Paper No. 466. Indian Society of Earthquake Technology. 42 (4): 203–212. ISSN 0972-0405.
Jump up ^ Robson, G. R. (1964). "An Earthquake Catalogue for the Eastern Caribbean 1530–1960" . Bulletin of the Seismological Society of America. 54 (2): 785–832.
Jump up ^ Feuillet, N.; Beauducel, F.; Tapponnier, P. (2011). "Tectonic context of moderate to large historical earthquakes in the Lesser Antilles and mechanical coupling with volcanoes". Journal of Geophysical Research. 116: B10308. Bibcode:2011JGRB..11610308F. doi:10.1029/2011JB008443.
^ Jump up to: a b Audemard M., Franck A.; Singer P., André (1996). "Active fault recognition in northwestern Venezuela and its seismogenic characterization: Neotectonic and paleoseismic approach". Geofísica Internacional. 35 (3): 245–255. Retrieved 24 November 2015.
Jump up ^ Deiros D (2000) [Determination of Displacement Between Caribbean and South American plates in Venezuela using Global Positioning System (GPS) data.] Geological Code of Venezuela. (in Spanish)
Jump up ^ Pérez OJ, Bilham R, Bendick R, Hernández N, Hoyer M, Velandia J, Moncayo C y Kozuch M (2001) Relative velocity between the Caribbean and South America plates from observations Within the Global Positioning System (GPS) in northern Venezuela.(in Spanish)
Jump up ^ James, K.H., Lorente, M.A. and Pindfell, J.L. (editors) (2009). The Origin and Evolution of the Caribbean Plate (PDF). London: The Geological Society of London. ISBN 978-1-86239-288-5. CS1 maint: Multiple names: authors list (link) CS1 maint: Extra text: authors list (link)
Jump up ^ Meschede, M.; Frisch W. (2002). "The evolution of the Caribbean Plate and its relation to global motion vectors: geometric constraints for an inter-american origin". In Jackson T. A. Caribbean geology: into the third millennium : transactions of the Fifteenth Caribbean Geological Conference. University of West Indies Press. p. 279. ISBN 978-976-640-100-9.
^ Jump up to: a b Marshall, L.G.; Sempere, T.; Butler, R.F. (1997). "Chronostratigraphy of the Mammal-Bearing Paleocene of South America" (PDF). Journal of South American Earth Sciences. 10 (1): 63. Bibcode:1997JSAES..10...49M. doi:10.1016/S0895-9811(97)00005-9.
External links[edit]
Tectonic reconstructions of the Caribbean region
NOAA Ocean Explorer
Caribbean Plate formation PDF file
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• Various, Authors. 2014. Enciclopedia de desastres naturales históricos de Colombia, 1-21. Universidad del Quindío. Accessed 2017-06-20.
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Entry point
From Wikipedia, the free encyclopedia
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For works of art titled "Point of Entry", see Point of Entry (disambiguation).
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (February 2014) (Learn how and when to remove this template message)
In computer programming, an entry point is where control is transferred from the operating system to a computer program, at which place the processor enters a program or a code fragment and execution begins. In some operating systems or programming languages, the initial entry is not part of the program but of the runtime library, in which case the runtime library initializes the program and then the runtime library enters the program. In other cases, the program may call the runtime library before doing anything when it is entered for the first time, and, after the runtime library returns, the actual code of the program begins to execute. This marks the transition from load time (and dynamic link time, if present) to run time.
In simple layouts, programs begin their execution at the beginning, which is common in scripting languages, simple binary executable formats, and boot loaders. In other cases, the entry point is at some other fixed point, which is some memory address than can be an absolute address or relative address (offset).
Alternatively, execution of a program can begin at a named point, either with a conventional name defined by the programming language or operating system, or at a caller-specified name. In many programming languages, notably C, this named point is a function called main; as a result, the entry point is often called the main function.
Contents
1 Usage
1.1 Contemporary
1.2 Historical
2 Exit point
3 Programming languages
3.1 APL
3.2 C and C++
3.3 C#
3.4 Clean
3.5 Common Lisp
3.6 D
3.7 FORTRAN
3.8 GNAT
3.9 Go
3.10 Haskell
3.11 Java
3.12 LOGO
3.13 OCaml
3.14 Pascal
3.15 Perl
3.16 PHP
3.17 Pike
3.18 Python
3.19 QB64
3.20 Ruby
3.21 Rust
3.22 Visual Basic
3.23 Xojo
4 See also
5 References
6 External links
Usage[edit]
Entry points apply both to source code and to executable files. However, in day-to-day software development, programmers specify the entry points only in source code, which makes them much better known. Entry points in executable files depend on the application binary interface (ABI) of the actual operating system, and are generated by the compiler or linker (if not fixed by the ABI). Non-executable object files may also have entry points, which are used later by the linker when generating entry points of an executable file.
Contemporary[edit]
In most of today's popular programming languages and operating systems, a computer program usually only has a single entry point.
In C, C++, D, Rust and Kotlin programs this is a function named main; in Java it is a static method named main (although the class must be specified at the invocation time), and in C# it is a static method named Main.[1][2]
In major operating systems, the standard executable format has a single entry point. In the Executable and Linkable Format (ELF), used in Unix and Unix-like systems such as Linux, the entry point is specified in the e_entry field of the ELF header. In the GNU Compiler Collection (gcc), the entry point used by the linker is the _start symbol. Similarly, in the Portable Executable format, used in Microsoft Windows, the entry point is specified by the AddressOfEntryPoint field, which is inherited from COFF. In COM files, the entry point is at the fixed offset of 0100h.
One notable modern exception to the single-entry-point paradigm is Android. Unlike applications on most other operating systems, Android applications do not have a single entry point – there is no main function, for example. Instead of a single entry point, they have essential components (which include activities and services) which the system can instantiate and run as needed.[3]
An occasionally used technique is the fat binary, which consists of several executables for different targets packaged in a single binary. Most commonly, this is implemented by a single overall entry point, which is compatible with all targets and branches to the target-specific entry point. Alternative techniques include storing separate executables in separate forks, each with its own entry point, which is then selected by the operating system.
Historical[edit]
Historically, and in some contemporary legacy systems, such as VMS and OS/400, computer programs have a multitude of entry points, each corresponding to the different functionalities of the program. The usual way to denote entry points, as used system-wide in VMS and in PL/I and MACRO programs, is to append them at the end of the name of the executable image, delimited by a dollar sign ($), e.g. directory.exe$make.
The Apple I computer also used this to some degree. For example, an alternative entry point in Apple I's BASIC would keep the BASIC program useful when the reset button was accidentally pushed.[clarification needed]
Exit point[edit]
In general, programs can exit at any time in an unstructured way, by returning to the operating system or crashing. Scripting languages typically end by reaching the end of the program, but for binaries the control must return to the operating system or it will simply run off the end of the process's memory, either executing whatever code is there or (in modern operating systems) resulting in a memory access violation and termination by the operating system.
Usually, there is not a single exit point specified in a program. However, in other cases runtimes ensure that programs always terminate in a structured way via a single exit point, which is guaranteed unless the runtime itself crashes; this allows cleanup code to be run, such as atexit handlers. This can be done by either requiring that programs terminate by returning from the main function, by calling a specific exit function, or by the runtime catching exceptions or operating system signals.
Programming languages[edit]
In many programming languages, the main function is where a program starts its execution. It enables high-level organization of the program's functionality, and typically has access to the command arguments given to the program when it was executed.
The main function is generally the first programmer-written function that runs when a program starts, and is invoked directly from the system-specific initialization contained in the runtime environment (crt0 or equivalent). However, some languages can execute user-written functions before main runs, such as the constructors of C++ global objects.
In other languages, notably scripting languages, execution simply begins at the start of the program.
A non-exhaustive list of programming languages follows, describing their way of defining the main entry point:
APL[edit]
In APL, when a workspace is loaded, the contents of "quad LX" (latent expression) variable is interpreted as an APL expression and executed.
C and C++[edit]
In C and C++, the function prototype of the main function looks like one of the following:
int main(void); int main(); int main(int argc, char **argv); int main(int argc, char *argv[]); int main(int argc, char **argv, char **env); // more specifically in C // NOT according to the ISO C standard 5.1.2.2.1 // BUT in embedded programming depending on the µC, this form is also used void main (void);
The parameters argc, argument count, and argv, argument vector,[4] respectively give the number and values of the program's command-line arguments. The names of argc and argv may be any valid identifier in C, but it is common convention to use these names. In C++, the names are to be taken literally, and the "void" in the parameter list is to be omitted, if strict conformance is desired.[5] Other platform-dependent formats are also allowed by the C and C++ standards, except that in C++ the return type must always be int;[6] for example, Unix (though not POSIX.1) and Windows have a third argument giving the program's environment, otherwise accessible through getenv in stdlib.h:
int main(int argc, char **argv, char **envp);
Darwin-based operating systems, such as macOS, have a fourth parameter containing arbitrary OS-supplied information, such as the path to the executing binary:[7]
int main(int argc, char **argv, char **envp, char **apple);
The value returned from the main function becomes the exit status of the process, though the C standard only ascribes specific meaning to two values: EXIT_SUCCESS (traditionally 0) and EXIT_FAILURE. The meaning of other possible return values is implementation-defined. In case a return value is not defined by the programmer, an implicit return 0; at the end of the main() function is inserted by the compiler; this behavior is required by the C++ standard.
It is guaranteed that argc is non-negative and that argv[argc] is a null pointer. By convention, the command-line arguments specified by argc and argv include the name of the program as the first element if argc is greater than 0; if a user types a command of "rm file", the shell will initialise the rm process with argc = 2 and argv = {"rm", "file", NULL}. As argv[0] is the name that processes appear under in ps, top etc., some programs, such as daemons or those running within an interpreter or virtual machine (where argv[0] would be the name of the host executable), may choose to alter their argv to give a more descriptive argv[0], usually by means of the exec system call.
The main() function is special; normally every C and C++ program must define it exactly once.
If declared, main() must be declared as if it has external linkage; it cannot be declared static or inline.
In C++, main() must be in the global namespace (i.e. ::main), cannot be overloaded, and cannot be a member function, although the name is not otherwise reserved, and may be used for member functions, classes, enumerations, or non-member functions in other namespaces. In C++ (unlike C) main() cannot be called recursively and cannot have its address taken.
C#[edit]
When executing a program written in C#, the CLR searches for a static method marked with the .entrypoint IL directive, which takes either no arguments, or a single argument of type string[], and has a return type of void or int, and executes it.[8]
static void Main(); static void Main(string[] args); static int Main(); static int Main(string[] args);
Command-line arguments are passed in args, similar to how it is done in Java. For versions of Main() returning an integer, similar to both C and C++, it is passed back to the environment as the exit status of the process.
Since C#7.1 there are four more possible signatures of the entry point, which allow asynchronous execution in the Main() Method.[9]
static Task Main() static Task<int> Main() static Task Main(string[]) static Task<int> Main(string[])
The Task and Task<int> types are the asynchronous equivalents of void and int.
Clean[edit]
Clean is a functional programming language based on graph rewriting. The initial node is called Start and is of type *World -> *World if it changes the world or some fixed type if the program only prints the result after reducing Start.
Start :: *World -> *World Start world = startIO ...
Or even simpler
Start :: String Start = "Hello, world!"
One tells the compiler which option to use to generate the executable file.
Common Lisp[edit]
ANSI Common Lisp does not define a main function; instead, the code is read and evaluated from top to bottom in a source file. However, the following code will emulate a main function.
(defun hello-main () (format t "Hello World!~%")) (hello-main)
D[edit]
In D, the function prototype of the main function looks like one of the following:
void main(); void main(string[] args); int main(); int main(string[] args);
Command-line arguments are passed in args, similar to how it is done in C# or Java. For versions of main() returning an integer, similar to both C and C++, it is passed back to the environment as the exit status of the process.
FORTRAN[edit]
FORTRAN does not have a main subroutine or function. Instead a PROGRAM statement as the first line can be used to specify that a program unit is a main program, as shown below. The PROGRAM statement cannot be used for recursive calls.[10]
PROGRAM HELLO PRINT *, "Cint!" END PROGRAM HELLO
Some versions of Fortran, such as those on the IBM System/360 and successor mainframes, do not support the PROGRAM statement. Many compilers from other software manufacturers will allow a fortran program to be compiled without a PROGRAM statement. In these cases, whatever module that has any non-comment statement where no SUBROUTINE, FUNCTION or BLOCK DATA statement occurs, is considered to be the Main program.
GNAT[edit]
Using GNAT, the programmer is not required to write a function called main; a source file containing a single subprogram can be compiled to an executable. The binder will however create a package ada_main, which will contain and export a C-style main function.
Go[edit]
In Go programming language, program execution starts with the main function of the package main
package main import "fmt" func main() { fmt.Println("Hello, World!") }
There is no way to access arguments or a return code outside of the standard library in Go. These can be accessed via os.Args and os.Exit respectively, both of which are included in the "os" package.
Haskell[edit]
A Haskell program must contain a name called main bound to a value of type IO t, for some type t;[11] which is usually IO (). IO is a monad, which organizes side-effects in terms of purely functional code.[12] The main value represents the side-effects-ful computation done by the program. The result of the computation represented by main is discarded; that is why main usually has type IO (), which indicates that the type of the result of the computation is (), the unit type, which contains no information.
main :: IO() main = putStrLn "Hello, World!"
Command line arguments are not given to main; they must be fetched using another IO action, such as System.Environment.getArgs.
Java[edit]
Java programs start executing at the main method, which has the following method heading:
public static void main(String[] args) public static void main(String... args) public static void main(String args[])
Command-line arguments are passed in args. As in C and C++, the name "main()" is special. Java's main methods do not return a value directly, but one can be passed by using the System.exit() method.
Unlike C, the name of the program is not included in args, because the name of the program is exactly the name of the class that contains the main method called, so it is already known. Also unlike C, the number of arguments need not be included, since arrays in Java have a field that keeps track of how many elements there are.
Another aspect unique to Java is that the main function must be included within a class, and then called manually by the runtime. This is because in Java everything has to be contained within a class. For instance, a hello world program in Java may look like so:
public class HelloWorld { public static void main(String[] args) { System.out.println("Hello, world!"); } }
To run this program, one must call java HelloWorld in the directory where the compiled class file (which itself must be named HelloWorld.class) exists. Alternatively, executable JAR files use a manifest file to specify the entry point in a manner that is filesystem-independent from the user's perspective.
LOGO[edit]
In FMSLogo, the procedures when loaded do not execute. To make them execute, it is necessary to use this code:
to procname
 ...                 ; Startup commands (such as print [Welcome])
end

make "startup [procname]

Note that the variable startup is used for the startup list of actions, but the convention is that this calls another procedure that runs the actions. That procedure may be of any name.
OCaml[edit]
OCaml has no main function. Programs are evaluated from top to bottom.
Command-line arguments are available in an array named Sys.argv and the exit status is 0 by default.
Example:
print_endline "Hello World"
Pascal[edit]
In Pascal, the main procedure is the only unnamed procedure in the program. Because Pascal programs have the procedures and functions in a more rigorous top-down order than C, C++ or Java programs, the main procedure is usually the last procedure in the program. Pascal does not have a special meaning for the name "main" or any similar name.
program Hello(Output); begin writeln('Hello, world!'); end.
Command-line arguments are counted in ParamCount and accessible as strings by ParamStr(n), with n between 0 and ParamCount.
Note that "unit" or "module" based versions of Pascal start the main module with the PROGRAM keyword, while other separately compiled modules start with UNIT (UCSD/Borland) or MODULE (ISO). The unnamed function in modules is often module initialization, and run before the main program starts.
Perl[edit]
In Perl, there is no main function. Statements are executed from top to bottom.
Command-line arguments are available in the special array @ARGV. Unlike C, @ARGV does not contain the name of the program, which is $0.
PHP[edit]
PHP does not have a "main" function. Starting from the first line of a PHP script, any code not encapsulated by a function header is executed as soon as it is seen.
Pike[edit]
In Pike syntax is similar to that of C and C++. The execution begins at main. The "argc" variable keeps the number of arguments passed to the program. The "argv" variable holds the value associated with the arguments passed to the program.
Example:
int main(int argc, array(string) argv)
Python[edit]
Python programs are evaluated top-to-bottom, as is usual in scripting languages: the entry point is the start of the source code. Since definitions must precede use, programs are typically structured with definitions at the top and the code to execute at the bottom (unindented), similar to code for a one-pass compiler, such as in Pascal.
Alternatively, a program can be structured with an explicit main function containing the code to be executed when a program is executed directly, but which can also be invoked by importing the program as a module and calling the function. This can be done by the following idiom, which relies on the internal variable __name__ being set to __main__ when a program is executed, but not when it is imported as a module (in which case it is instead set to the module name); there are many variants of this structure:[13][14][15]
import sys def main(argv): n = int(argv[1]) print(n + 1) if __name__ == '__main__': sys.exit(main(sys.argv))
In this idiom, the call to the named entry point main is explicit, and the interaction with the operating system (receiving the arguments, calling system exit) are done explicitly by library calls, which are ultimately handled by the Python runtime. This contrast with C, where these are done implicitly by the runtime, based on convention.
QB64[edit]
The QB64 language has no main function, the code that is not within a function, or subroutine is executed first, from top to bottom:
print "Hello World! a ="; a = getInteger(1.8d): print a function getInteger(n as double) getInteger = int(n) end function
Command line arguments (if any) can be read using the COMMAND$ function:
dim shared commandline as string commandline = COMMAND$ 'Several space-separared command line arguments can be read using COMMAND$(n) commandline1 = COMMAND$(2)
Ruby[edit]
In Ruby, there is no distinct main function. The code written without additional "class .. end", "module .. end" enclosures is executed directly, step by step, in context of special "main" object. This object can be referenced using:
irb(main):001:0> self => main
and contain the following properties:
irb(main):002:0> self.class => Object irb(main):003:0> self.class.ancestors => [Object, Kernel, BasicObject]
Methods defined without additional classes/modules are defined as private methods of the "main" object, and, consequently, as private methods of almost any other object in Ruby:
irb(main):004:0> def foo irb(main):005:1> 42 irb(main):006:1> end => nil irb(main):007:0> foo => 42 irb(main):008:0> [].foo NoMethodError: private method `foo' called for []:Array from (irb):8 from /usr/bin/irb:12:in `<main>' irb(main):009:0> false.foo NoMethodError: private method `foo' called for false:FalseClass from (irb):9 from /usr/bin/irb:12:in `<main>'
Number and values of command-line arguments can be determined using the single ARGV constant array:
$ irb /dev/tty foo bar tty(main):001:0> ARGV ARGV => ["foo", "bar"] tty(main):002:0> ARGV.size ARGV.size => 2
Note that first element of ARGV, ARGV[0], contains the first command-line argument, not the name of program executed, as in C. The name of program is available using $0 or $PROGRAM_NAME.[16]
Similar to Python, one could use:
if __FILE__ == $PROGRAM_NAME # Put "main" code here end
Rust[edit]
fn main() { }
Visual Basic[edit]
In Visual Basic, when a project contains no forms, the startup object may be the Main() procedure. The Command$ function can be optionally used to access the argument portion of the command line used to launch the program:
Sub Main() Debug.Print "Hello World!" MsgBox "Arguments if any are: " & Command$ End Sub
Xojo[edit]
In Xojo, there are two different project types, each with a different main entry point. Desktop (GUI) applications start with the App.Open event of the project's Application object. Console applications start with the App.Run event of the project's ConsoleApplication object. In both instances, the main function is automatically generated, and cannot be removed from the project.
See also[edit]
Computer programming portal
Basic block
crt0, a set of execution startup routines linked into a C program
Runtime system
References[edit]
Jump up ^ "The main() function". ibm.com. IBM. Retrieved 2014-05-08.
Jump up ^ "Main() and Command-Line Arguments (C# Programming Guide)". Msdn.microsoft.com. Retrieved 2014-05-08.
Jump up ^ "Application Fundamentals". Android Development. linuxtopia.org. Retrieved 2014-02-19.
Jump up ^ argv: the vector term in this variable's name is used in traditional sense to refer to strings.
Jump up ^ Parameter types and names of main
Jump up ^ Section 3.6.1.2, Standard C++ 2011 edition.
Jump up ^ The char *apple Argument Vector
Jump up ^ "Console Applications in .NET, or Teaching a New Dog Old Tricks". Msdn.microsoft.com. 2003-06-12. Retrieved 2013-08-19.
Jump up ^ https://github.com/dotnet/csharplang/blob/master/proposals/csharp-7.1/async-main.md. Missing or empty |title= (help)
Jump up ^ XL FORTRAN for AIX. Language Reference. Third Edition, 1994. IBM
Jump up ^ "The Haskell 98 Report: Modules". Haskell.org. Retrieved 2013-08-19.
Jump up ^ Some Haskell Misconceptions: Idiomatic Code, Purity, Laziness, and IO — on Haskell's monadic IO>
Jump up ^ Guido van Rossum (May 15, 2003). "Python main() functions", comments
Jump up ^ Code Like a Pythonista: Idiomatic Python—on Python scripts used as modules
Jump up ^ Ned Batchelder (6 June 2003). "Python main() functions".
Jump up ^ Programming Ruby: The Pragmatic Programmer's Guide, Ruby and Its World — on Ruby ARGV
External links[edit]
Hello from a libc-free world! (Part 1), March 16, 2010
How main method works in Java
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