Synchronization is the coordination of events to operate a system in unison. 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.

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

Firefighters in Parade
Firefighters marching in a parade


Time-keeping and synchronization of clocks has been 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 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 time between adjacent towns to be noticeable. Each line handled the problem by synchronizing all its stations to headquarters as a standard railroad time. In some territories, sharing of single railroad tracks was controlled by the timetable. The need for strict timekeeping led the companies to settle on one standard, and civil authorities eventually abandoned local mean solar time in favor of that standard.


In electrical engineering terms, for digital logic and data transfer, a synchronous circuit requires a clock signal. However, the use of the word "clock" in this sense is different from the typical sense of a clock as a device that keeps track of time-of-day; the clock signal simply signals the start and/or end of some time period, often very minute (measured in microseconds or nanoseconds), that has an arbitrary relationship to sidereal, solar, or lunar time, or 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. (Albert Einstein proved in 1905 in his first relativity paper that there actually are no such things as absolutely simultaneous events.) 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

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] however 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]


  • 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.
  • 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.
  • Film, video, and audio applications use time code to synchronize audio and video.
  • Flash photography, see Flash synchronization

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


  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.
  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 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 2017-02-02.
  7. ^ a b 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.
  12. ^ Reddish, Paul; Fischer, Ronald; Bulbulia, Joseph (1 January 2013). "Let's dance together: synchrony, shared intentionality and cooperation". PLoS One. 8 (8): e71182. 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.

External links

Analog television

Analog television or analogue television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by rapid variations of either the amplitude, frequency or phase of the signal.

Analog signals vary over a continuous range of possible values which means that electronic noise and interference becomes reproduced by the receiver. Thus with analog, a moderately weak signal becomes snowy and subject to interference. In contrast, a moderately weak digital signal and a very strong digital signal transmit equal picture quality. Analog television may be wireless (terrestrial television and satellite television) or can be distributed over a cable network using cable converters (cable television).

All broadcast television systems used analog signals before the arrival of digital television (DTV). Motivated by the lower bandwidth requirements of compressed digital signals, since the 2000s a digital television transition is proceeding in most countries of the world, with different deadlines for cessation of analog broadcasts.

Barrier (computer science)

In parallel computing, a barrier is a type of synchronization method. A barrier for a group of threads or processes in the source code means any thread/process must stop at this point and cannot proceed until all other threads/processes reach this barrier.

Many collective routines and directive-based parallel languages impose implicit barriers. For example, a parallel do loop in Fortran with OpenMP will not be allowed to continue on any thread until the last iteration is completed. This is in case the program relies on the result of the loop immediately after its completion. In message passing, any global communication (such as reduction or scatter) may imply a barrier.

Browser synchronization

Browser synchronization (often simply called sync) is a free cloud service provided by a web browser vendor for sharing settings and data across multiple installs. This is typically used to maintain a consistent browser setup on multiple devices. The user must be logged-in to their account to sync a browser.

Comparison of file synchronization software

This is a list of file synchronization software. File synchronization is a process of ensuring that files in two or more locations are updated via certain rules.

File synchronization

File synchronization (or syncing) in computing is the process of ensuring that computer files in two or more locations are updated via certain rules.

In one-way file synchronization, also called mirroring, updated files are copied from a 'source' location to one or more 'target' locations, but no files are copied back to the source location. In two-way file synchronization, updated files are copied in both directions, usually with the purpose of keeping the two locations identical to each other. In this article, the term synchronization refers exclusively to two-way file synchronization.

File synchronization is commonly used for home backups on external hard drives or updating for transport on USB flash drives. BitTorrent Sync, Dropbox and SKYSITE are prominent products. Some backup software also support real-time file sync. The automatic process prevents copying already identical files and thus can be faster and save much time versus a manual copy, and is less error prone. However this suffers from the limit that the synchronized files must physically fit in the portable storage device. Synchronization software that only keeps a list of files and the changed files eliminates this problem (e.g. the "snapshot" feature in Beyond Compare or the "package" feature in Synchronize It!). It is especially useful for mobile workers, or others that work on multiple computers.

It is possible to synchronize multiple locations by synchronizing them one pair at a time. The Unison Manual describes how to do this:

If you need to do this, the most reliable way to set things up is to organize the machines into a "star topology," with one machine designated as the "hub" and the rest as "spokes," and with each spoke machine synchronizing only with the hub. The big advantage of the star topology is that it eliminates the possibility of confusing "spurious conflicts" arising from the fact that a separate archive is maintained by Unison for every pair of hosts that it synchronizes.

Flash synchronization

In a camera, flash synchronization is defined as synchronizing the firing of a photographic flash with the opening of the shutter admitting light to photographic film or electronic image sensor. It is often shortened to flash sync or flash synch.

In cameras with mechanical (clockwork) shutters synchronization is supported by an electrical contact within the shutter mechanism, which closes the circuit at the appropriate moment in the shutter opening process. In electronic digital cameras, the mechanism is usually a programmable electronic timing circuit, which may, in some cameras, take input from a mechanical shutter contact. The flash is connected electrically to the camera either by a cable with a standardised coaxial PC (for Prontor/Compur) 3.5 mm (1/8") connector (as defined in ISO 519), or via contacts in an accessory mount (hot shoe) bracket.

Faster shutter speeds are often better when there is significant ambient illumination, and flash is used to flash-fill subjects that are backlit without motion blur, or to increase depth of field by using a small aperture. In another creative use, the photographer of a moving subject may deliberately combine a slow shutter speed with flash exposure in order to record motion blur of the ambient-lit regions of the image superimposed on the flash-lit regions.


Gleichschaltung (German pronunciation: [ˈɡlaɪçʃaltʊŋ]), or in English co-ordination, was in Nazi terminology the process of Nazification by which Adolf Hitler and the Nazi Party successively established a system of totalitarian control and coordination over all aspects of German society, "from the economy and trade associations to the media, culture and education".The apex of the Nazification of Germany was in the resolutions approved during the Nuremberg Rally of 1935, when the symbols of the Nazi Party and the State were fused (see Flag of Germany) and German Jews were deprived of their citizenship (see Nuremberg Laws).

Google Sync

Google Sync was a file synchronization service from Google that provided over-the-air synchronization of Gmail, Google Contacts, and Google Calendar with PC and mobile device Mail, Calendar and Address Book applications. It used Microsoft® Exchange ActiveSync® to let service users synchronize their Google Apps mail, contacts, and calendars to their mobile devices, wherein the users can also set up or customize the alerts for incoming messages and upcoming meetings. Google Sync worked with PC, Mac, Linux, Android, BlackBerry, Symbian S60, iPhone, iPad, Windows Mobile, and other devices. Google Sync was announced in February 2009 and discontinued for non-business users in December 2012.

Language Of Temporal Ordering Specification

Language Of Temporal Ordering Specification (LOTOS) is a formal specification language based on temporal ordering of events. LOTOS is used for protocol specification in ISO OSI standards.

LOTOS is an algebraic language that consists of two parts: a part for the description of data and operations, based on abstract data types, and a part for the description of concurrent processes, based on process calculus.

Work on the standard was completed in 1988, and it was published as ISO 8807 in 1989. Between 1993 and 2001, an ISO committee worked to define a revised version of the LOTOS standard, which was published in 2001 as E-LOTOS.

Lip sync

Lip sync (short for lip synchronization) is a technical term for matching a speaking or singing person's lip movements with prerecorded sung or spoken vocals that listeners hear, either through the sound reinforcement system in a live performance or via television, computer, cinema speakers, or generally anything with audio output in other cases. The term can refer to any of a number of different techniques and processes, in the context of live performances and audiovisual recordings.

In film production, lip-synching is often part of the postproduction phase. Dubbing foreign-language films and making animated characters appear to speak both require elaborate lip-synching. Many video games make extensive use of lip-synced sound files to create an immersive environment in which on-screen characters appear to be speaking. In the music industry, lip-synching is used by singers for music videos, television and film appearances and some types of live performances. Lip-syncing by singers can be controversial to fans attending concert performances who expect to view a live performance.

Microsoft Sync Framework

Microsoft Sync Framework is a data synchronization platform from Microsoft that can be used to synchronize data across multiple data stores. Sync Framework includes a transport-agnostic architecture, into which data store-specific synchronization providers, modelled on the ADO.NET data provider API, can be plugged in. Sync Framework can be used for offline access to data, by working against a cached set of data and submitting the changes to a master database in a batch, as well as to synchronize changes to a data source across all consumers (publish/subscribe sync) and peer-to-peer synchronization of multiple data sources. Sync Framework features built-in capabilities for conflict detection – whether data to be changed has already been updated – and can flag them for manual inspection or use defined policies to try to resolve the conflict. Sync Services includes an embedded SQL Server Compact database to store metadata about the synchronization relationships as well as about each sync attempt. The Sync Framework API is surfaced both in managed code, for use with .NET Framework applications, as well as unmanaged code, for use with COM applications. It was scheduled to ship with Visual Studio 2008 in late November 2007.

Network Time Protocol

The Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use. NTP was designed by David L. Mills of the University of Delaware.

NTP is intended to synchronize all participating computers to within a few milliseconds of Coordinated Universal Time (UTC). It uses the intersection algorithm, a modified version of Marzullo's algorithm, to select accurate time servers and is designed to mitigate the effects of variable network latency. NTP can usually maintain time to within tens of milliseconds over the public Internet, and can achieve better than one millisecond accuracy in local area networks under ideal conditions. Asymmetric routes and network congestion can cause errors of 100 ms or more.The protocol is usually described in terms of a client-server model, but can as easily be used in peer-to-peer relationships where both peers consider the other to be a potential time source. Implementations send and receive timestamps using the User Datagram Protocol (UDP) on port number 123. They can also use broadcasting or multicasting, where clients passively listen to time updates after an initial round-trip calibrating exchange. NTP supplies a warning of any impending leap second adjustment, but no information about local time zones or daylight saving time is transmitted.The current protocol is version 4 (NTPv4), which is a proposed standard as documented in RFC 5905. It is backward compatible with version 3, specified in RFC 1305.

Neural oscillation

Neural oscillations, or brainwaves, are rhythmic or repetitive patterns of neural activity in the central nervous system. Neural tissue can generate oscillatory activity in many ways, driven either by mechanisms within individual neurons or by interactions between neurons. In individual neurons, oscillations can appear either as oscillations in membrane potential or as rhythmic patterns of action potentials, which then produce oscillatory activation of post-synaptic neurons. At the level of neural ensembles, synchronized activity of large numbers of neurons can give rise to macroscopic oscillations, which can be observed in an electroencephalogram. Oscillatory activity in groups of neurons generally arises from feedback connections between the neurons that result in the synchronization of their firing patterns. The interaction between neurons can give rise to oscillations at a different frequency than the firing frequency of individual neurons. A well-known example of macroscopic neural oscillations is alpha activity.

Neural oscillations were observed by researchers as early as 1924 (by Hans Berger). More than 50 years later, intrinsic oscillatory behavior was encountered in vertebrate neurons, but its functional role is still not fully understood. The possible roles of neural oscillations include feature binding, information transfer mechanisms and the generation of rhythmic motor output. Over the last decades more insight has been gained, especially with advances in brain imaging. A major area of research in neuroscience involves determining how oscillations are generated and what their roles are. Oscillatory activity in the brain is widely observed at different levels of organization and is thought to play a key role in processing neural information. Numerous experimental studies support a functional role of neural oscillations; a unified interpretation, however, is still lacking.

Precision Time Protocol

The Precision Time Protocol (PTP) is a protocol used to synchronize clocks throughout a computer network. On a local area network, it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems. PTP is currently employed to synchronize financial transactions, mobile phone tower transmissions, sub-sea acoustic arrays, and networks that require precise timing but lack access to satellite navigation signals.

PTP was originally defined in the IEEE 1588-2002 standard, officially entitled "Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems" and published in 2002. In 2008, IEEE 1588-2008 was released as a revised standard; also known as PTP Version 2, it improves accuracy, precision and robustness but is not backward compatible with the original 2002 version.According to John Eidson, who led the IEEE 1588-2002 standardization effort, "IEEE 1588 is designed to fill a niche not well served by either of the two dominant protocols, NTP and GPS. IEEE 1588 is designed for local systems requiring accuracies beyond those attainable using NTP. It is also designed for applications that cannot bear the cost of a GPS receiver at each node, or for which GPS signals are inaccessible."


A Prontor-Compur connection (also known as a PC connector, PC terminal, or PC socket) is a standard 3.5 mm (1/8") electrical connector (as defined in ISO 519) used in photography to synchronize the shutter to the flash.

Synchronization (computer science)

In computer science, synchronization refers to one of two distinct but related concepts: synchronization of processes, and synchronization of data. Process synchronization refers to the idea that multiple processes are to join up or handshake at a certain point, in order to reach an agreement or commit to a certain sequence of action. Data synchronization refers to the idea of keeping multiple copies of a dataset in coherence with one another, or to maintain data integrity. Process synchronization primitives are commonly used to implement data synchronization.

Synchronization gear

A synchronization gear, or a gun synchronizer, sometimes rather less accurately called an interrupter, is attached to the armament of a single-engine tractor-configuration aircraft so it can fire through the arc of its spinning propeller without bullets striking the blades. The idea presupposes a fixed armament directed by aiming the aircraft in which it is fitted at the target, rather than aiming the gun independently.

There are many practical problems, mostly arising from the inherently imprecise nature of an automatic gun's firing, the great (and varying) velocity of the blades of a spinning propeller, and the very high speed at which any gear synchronizing the two has to operate.

Design and experimentation with gun synchronization had been underway in France and Germany in 1913–1914, following the ideas of August Euler, who seems to have been the first to suggest mounting a fixed armament firing in the direction of flight (in 1910). However, the first practical—if far from reliable—gear to enter operational service was that fitted to the Eindecker monoplane fighters, which entered squadron service with the German Air Service in mid-1915. The success of the Eindecker led to numerous gun synchronization devices, culminating in the reasonably reliable hydraulic British Constantinesco gear of 1917. By the end of the war German engineers were well on the way to perfecting a gear using an electrical rather than a mechanical or hydraulic link between the engine and the gun, with the gun being triggered by a solenoid rather than by a mechanical "trigger motor".

From 1918 to the mid-1930s the standard armament for a fighter aircraft remained two synchronized rifle calibre machine guns, firing forward through the propeller. During the late-1930s, however, the main role of the fighter was increasingly seen as the destruction of large, all-metal bombers, for which the "traditional" light armament was inadequate.

Since it was impractical to try to fit more than one or two extra guns in the limited space available in the front of a single-engine aircraft's fuselage, this led to an increasing proportion of the armament being mounted in the wings, firing outside the arc of the propeller. There were in fact some advantages in dispensing with centrally mounted guns altogether. Nevertheless, the conclusive redundancy of synchronization gears did not finally come until the introduction of jet propulsion and the absence of a propeller for guns to be synchronized with.

Synchronization of chaos

Synchronization of chaos is a phenomenon that may occur when two, or more, dissipative chaotic systems are coupled.

Because of the exponential divergence of the nearby trajectories of chaotic systems, having two chaotic systems evolving in synchrony might appear surprising. However, synchronization of coupled or driven chaotic oscillators is a phenomenon well established experimentally and reasonably well-understood theoretically.

The stability of synchronization for coupled systems can be analyzed using master stability. Synchronization of chaos is a rich phenomenon and a multi-disciplinary subject with a broad range of applications.Synchronization may present a variety of forms depending on the nature of the interacting systems and the type of coupling, and the proximity between the systems.

Windows Mobile Device Center

Windows Mobile Device Center is a synchronization software program developed by Microsoft, and the successor to ActiveSync. It is designed to synchronize various content including music, video, contacts, calendar events, web browser favorites, and other files between Windows Mobile devices and the Microsoft Windows operating system.

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