Synchronization

Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or in time. Systems that operate with all parts in synchrony are said to be synchronous or in sync—and those that are not are asynchronous.

For other uses, see Synchronization (disambiguation).

Synchronized dancers

Today, time synchronization can occur between systems around the world through satellite navigation signals.

Transport

Time-keeping and synchronization of clocks is a critical problem in long-distance ocean navigation. Before radio navigation and satellite-based navigation, navigators required accurate time in conjunction with astronomical observations to determine how far east or west their vessel traveled. The invention of an accurate marine chronometer revolutionized marine navigation. By the end of the 19th century, important ports provided time signals in the form of a signal gun, flag, or dropping time ball so that mariners could check and correct their chronometers for error.

Synchronization was important in the operation of 19th-century railways, these being the first major means of transport fast enough for differences in local mean time between nearby towns to be noticeable. Each line handled the problem by synchronizing all its stations to headquarters as a standard railway time. In some territories, companies shared a single railroad track and needed to avoid collisions. The need for strict timekeeping led the companies to settle on one standard, and civil authorities eventually abandoned local mean time in favor of railway time.

Communication
Further information: Synchronization in telecommunications

In electrical engineering terms, for digital logic and data transfer, a synchronous circuit requires a clock signal. A clock signal simply signals the start or end of some time period, often measured in microseconds or nanoseconds, that has an arbitrary relationship to any other system of measurement of the passage of minutes, hours, and days.

In a different sense, electronic systems are sometimes synchronized to make events at points far apart appear simultaneous or near-simultaneous from a certain perspective.[lower-alpha 1] Timekeeping technologies such as the GPS satellites and Network Time Protocol (NTP) provide real-time access to a close approximation to the UTC timescale and are used for many terrestrial synchronization applications of this kind.

Synchronization is an important concept in the following fields:

Dynamical systems
See also: Synchronization of chaos

Synchronization of multiple interacting dynamical systems can occur when the systems are autonomous oscillators. For instance, integrate-and-fire oscillators with either two-way (symmetric) or one-way coupling can synchronize when the strength of the coupling (in frequency units) is greater than the differences among the free-running natural oscillator frequencies. Poincare phase oscillators are model systems that can interact and partially synchronize within random or regular networks.[1] In the case of global synchronization of phase oscillators, an abrupt transition from unsynchronized to full synchronization takes place when the coupling strength exceeds a critical threshold. This is known as the Kuramoto model phase transition. Synchronization is an emergent property that occurs in a broad range of dynamical systems, including neural signaling, the beating of the heart and the synchronization of fire-fly light waves.

Human movement

Synchronization of movement is defined as similar movements between two or more people who are temporally aligned.[2] This is different to mimicry, as these movements occur after a short delay.[3] Muscular bonding is the idea that moving in time evokes particular emotions.[4] This sparked some of the first research into movement synchronization and its effects on human emotion.

In groups, synchronization of movement has been shown to increase conformity,[5] cooperation and trust.[6] Military step has long been used for these purposes but more research on group synchronization is needed to determine its effects on the group as a whole and on individuals within a group. In dyads, groups of two people, synchronization has been demonstrated to increase affiliation,[7] self-esteem,[8] compassion and altruistic behaviour[9] and increase rapport.[10] During arguments, synchrony between the arguing pair has been noted to decrease, however it is not clear whether this is due to the change in emotion or other factors.[11] There is evidence to show that movement synchronization requires other people to cause its beneficial effects, as the effect on affiliation does not occur when one of the dyad is synchronizing their movements to something outside the dyad.[7] This is known as interpersonal synchrony.

There has been dispute regarding the true effect of synchrony in these studies. Research in this area detailing the positive effects of synchrony, have attributed this to synchrony alone; however, many of the experiments incorporate a shared intention to achieve synchrony. Indeed, the Reinforcement of Cooperation Model suggests that perception of synchrony leads to reinforcement that cooperation is occurring, which leads to the pro-social effects of synchrony.[12] More research is required to separate the effect of intentionality from the beneficial effect of synchrony.[13]

Uses
  • Film synchronization of image and sound in sound film. Synchronization is important in fields such as digital telephony, video and digital audio where streams of sampled data are manipulated. More sophisticated film, video, and audio applications use time code to synchronize audio and video.
  • Synchronization of video frames from multiple cameras for 3D reconstruction[14]
  • In electric power systems, alternator synchronization is required when multiple generators are connected to an electrical grid.
  • Arbiters are needed in digital electronic systems such as microprocessors to deal with asynchronous inputs. There are also electronic digital circuits called synchronizers that attempt to perform arbitration in one clock cycle. Synchronizers, unlike arbiters, are prone to failure. (See metastability in electronics).
  • Encryption systems usually require some synchronization mechanism to ensure that the receiving cipher is decoding the right bits at the right time.
  • Automotive transmissions contain synchronizers that bring the toothed rotating parts (gears and splined shaft) to the same rotational velocity before engaging the teeth.
  • Flash synchronization synchronizes the flash with the shutter.

Some systems may be only approximately synchronized, or plesiochronous. Some applications require that relative offsets between events be determined. For others, only the order of the event is important.

See also
Order synchronization and related topics
Video and audio engineering
Aircraft gun engineering
Compare with

Notes
  1. Albert Einstein proved in 1905 in his first relativity paper that there actually are no such things as absolutely simultaneous events.

References
  1. Nolte, David (2015). Introduction to Modern Dynamics: Chaos, Networks, Space and Time. Oxford University Press.
  2. Condon, W. S.; Ogston, W. D. (1 October 1966). "Sound film analysis of normal and pathological behavior patterns". The Journal of Nervous and Mental Disease. 143 (4): 338–347. doi:10.1097/00005053-196610000-00005. ISSN 0022-3018. PMID 5958766. S2CID 19384588.
  3. Richardson, Michael J.; Marsh, Kerry L.; Schmidt, R. C. (1 February 2005). "Effects of visual and verbal interaction on unintentional interpersonal coordination". Journal of Experimental Psychology. Human Perception and Performance. 31 (1): 62–79. CiteSeerX 10.1.1.176.8093. doi:10.1037/0096-1523.31.1.62. ISSN 0096-1523. PMID 15709863.
  4. McNeill, William Hardy (30 September 1997). Keeping Together in Time. hdl:2027/heb.04002.0001.001. ISBN 978-0-674-50230-7.
  5. Dong, Ping; Dai, Xianchi; Wyer, Robert S. (1 January 2015). "Actors conform, observers react: the effects of behavioral synchrony on conformity". Journal of Personality and Social Psychology. 108 (1): 60–75. doi:10.1037/pspi0000001. ISSN 1939-1315. PMID 25437130.
  6. "Synchrony and Cooperation – PubMed – Search Results". Retrieved 2 February 2017.
  7. Hove, Michael J.; Risen, Jane L. (2009). "It's All in the Timing: Interpersonal Synchrony Increases Affiliation". Social Cognition. 27 (6): 949. doi:10.1521/soco.2009.27.6.949.
  8. Lumsden, Joanne; Miles, Lynden K.; Macrae, C. Neil (1 January 2014). "Sync or sink? Interpersonal synchrony impacts self-esteem". Frontiers in Psychology. 5: 1064. doi:10.3389/fpsyg.2014.01064. PMC 4168669. PMID 25285090.
  9. Valdesolo, Piercarlo; Desteno, David (1 April 2011). "Synchrony and the social tuning of compassion". Emotion. 11 (2): 262–266. doi:10.1037/a0021302. ISSN 1931-1516. PMID 21500895.
  10. Vacharkulksemsuk, Tanya; Fredrickson, Barbara L. (1 January 2012). "Strangers in sync: Achieving embodied rapport through shared movements". Journal of Experimental Social Psychology. 48 (1): 399–402. doi:10.1016/j.jesp.2011.07.015. ISSN 0022-1031. PMC 3290409. PMID 22389521.
  11. Paxton, Alexandra; Dale, Rick (1 January 2013). "Argument disrupts interpersonal synchrony". Quarterly Journal of Experimental Psychology. 66 (11): 2092–2102. doi:10.1080/17470218.2013.853089. ISSN 1747-0226. PMID 24303888. S2CID 9565508.
  12. Reddish, Paul; Fischer, Ronald; Bulbulia, Joseph (1 January 2013). "Let's dance together: synchrony, shared intentionality and cooperation". PLOS ONE. 8 (8): e71182. Bibcode:2013PLoSO...871182R. doi:10.1371/journal.pone.0071182. ISSN 1932-6203. PMC 3737148. PMID 23951106.
  13. Ellamil, Melissa; Berson, Josh; Margulies, Daniel S. (1 January 2016). "Influences on and Measures of Unintentional Group Synchrony". Frontiers in Psychology. 7: 1744. doi:10.3389/fpsyg.2016.01744. PMC 5101201. PMID 27881968.
  14. Moore, Carl, et al. "Synchronization of images from multiple cameras to reconstruct a moving human." 2010 IEEE/ACM 14th International Symposium on Distributed Simulation and Real Time Applications. IEEE, 2010.
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