Synchronization is the coordination of events to operate a

system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment (systems), environment, is described by its boundaries, ...

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 Asynchrony is the state of not being in synchronization. Asynchrony or asynchronous may refer to: Electronics and computing * Asynchrony (computer programming), the occurrence of events independent of the main program flow, and ways to deal with ...

''. Today, time synchronization can occur between systems around the world through

satellite navigation A satellite navigation or satnav system is a system that uses satellites to provide autonomous geo-spatial positioning. It allows satellite navigation devices to determine their location (longitude, latitude, and altitude/elevation) to high pr ...

signals and other

time and frequency transfer Time and frequency transfer is a scheme where multiple sites share a precise reference time or frequency. The technique is commonly used for creating and distributing standard time scales such as International Atomic Time (TAI). Time transfer sol ...

techniques.

Navigation and railways

Time-keeping and synchronization of clocks is a critical problem in long-distance ocean navigation. Before

radio navigation Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination. The basic principles a ...

and satellite-based navigation, navigators required accurate

time Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...

in conjunction with astronomical observations to determine how far east or west their vessel traveled. The invention of an accurate

marine chronometer A marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation. It is used to determine longitude by comparing Greenwich Mean Time (GMT), or in the modern ...

revolutionized marine navigation. By the end of the 19th century, important ports provided

time signal A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, audi ...

s in the form of a signal gun, flag, or dropping

time ball A time ball or timeball is a time-signalling device. It consists of a large, painted wooden or metal ball that is dropped at a predetermined time, principally to enable navigators aboard ships offshore to verify the setting of their marine chron ...

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 Local mean time (LMT) is a form of solar time that corrects the variations of Solar time#Apparent solar time, local apparent time, forming a uniform time scale at a specific longitude. This measurement of time was used for everyday use during the ...

between nearby towns to be noticeable. Each line handled the problem by synchronizing all its stations to headquarters as a standard

railway time Railway time was the standardised time arrangement first applied by the Great Western Railway in England in November 1840, the first recorded occasion when different local mean times were synchronised and a single standard time applied. The key ...

. 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

electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems which use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...

terms, for digital logic and data transfer, a

synchronous circuit In digital electronics, a synchronous circuit is a digital circuit in which the changes in the state of memory elements are synchronized by a clock signal. In a sequential digital logic circuit, data are stored in memory devices called flip-fl ...

requires a

clock signal In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits. A clock sign ...

. 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. Timekeeping technologies such as the

GPS The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...

satellites and

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 c ...

(NTP) provide real-time access to a close approximation to the UTC timescale and are used for many terrestrial synchronization applications of this kind. In

computer science Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...

(especially

parallel computing Parallel computing is a type of computation in which many calculations or processes are carried out simultaneously. Large problems can often be divided into smaller ones, which can then be solved at the same time. There are several different fo ...

), synchronization is the coordination of simultaneous threads or processes to complete a task with correct runtime order and no unexpected

race condition A race condition or race hazard is the condition of an electronics, software, or other system where the system's substantive behavior is dependent on the sequence or timing of other uncontrollable events. It becomes a bug when one or more of t ...

s; see

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 handshak ...

for details. Synchronization is also an important concept in the following fields: *

Cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...

Lip sync Lip sync or lip synch (pronounced , the same as the word ''sink'', short for lip synchronization) is a technical term for matching a speaking or singing person's lip movements with sung or spoken vocals. Audio for lip syncing is generated thr ...

Multimedia Multimedia is a form of communication that uses a combination of different content forms such as text, audio, images, animations, or video into a single interactive presentation, in contrast to tradition ...

Rhythm Rhythm (from Greek , ''rhythmos'', "any regular recurring motion, symmetry") generally means a " movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions". This general meaning of regular recu ...

Neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...

* Photography *

Physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...

(The idea of

simultaneity Simultaneity may refer to: * Relativity of simultaneity, a concept in special relativity. * Simultaneity (music), more than one complete musical texture occurring at the same time, rather than in succession * Simultaneity, a concept in Endogeneit ...

has many difficulties, both in practice and theory.) *

Synthesizers A synthesizer (also spelled synthesiser) is an electronic musical instrument that generates audio signals. Synthesizers typically create sounds by generating waveforms through methods including subtractive synthesis, additive synthesis and ...

* Telecommunication **

Frame synchronization In telecommunication, frame synchronization or framing is the process by which, while receiving a stream of framed data, incoming frame alignment signals (i.e., a distinctive bit sequences or syncwords) are identified (that is, distinguished from ...

Synchronization (video) In video, frame synchronization is the process of synchronizing display pixel scanning to a synchronization source. When several systems are connected, a synchronization signal is fed from the synchronization source to the other systems in the ne ...

Dynamical systems

Synchronization of multiple interacting

dynamical system In mathematics, a dynamical system is a system in which a Function (mathematics), function describes the time dependence of a Point (geometry), point in an ambient space. Examples include the mathematical models that describe the swinging of a ...

s can occur when the systems are autonomous oscillators. Poincaré phase oscillators are model systems that can interact and partially synchronize within random or regular networks. 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 The Kuramoto model (or Kuramoto–Daido model), first proposed by , is a mathematical model used to describing synchronization. More specifically, it is a model for the behavior of a large set of coupled oscillators. Its formulation was motivated ...

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.

Applications

Neuroscience

In cognitive neuroscience, (stimulus-dependent) (phase-)synchronous oscillations of neuron populations serve to solve the general "

binding problem The consciousness and binding problem is the problem of how objects, background and abstract or emotional features are combined into a single experience. The binding problem refers to the overall encoding of our brain circuits for the combination o ...

". According to the so-called "Binding-By-Synchrony (BBS) Hypothesis" a precise temporal correlation between the impulses of neurons ("cross-correlation analysis") and thus a stimulus-dependent temporal synchronization of the coherent activity of subpopulations of neurons emerges. Moreover, this synchronization mechanism circumvents the "superposition problem" by more effectively identifying the signature of synchronous neuronal signals as belonging together for subsequent (sub-)cortical information processing areas.

Cognitive science

In cognitive science, integrative (phase) synchronization

mechanism Mechanism may refer to: *Mechanism (engineering), rigid bodies connected by joints in order to accomplish a desired force and/or motion transmission *Mechanism (biology), explaining how a feature is created *Mechanism (philosophy), a theory that a ...

s in cognitive neuroarchitectures of modern

connectionism Connectionism refers to both an approach in the field of cognitive science that hopes to explain mental phenomena using artificial neural networks (ANN) and to a wide range of techniques and algorithms using ANNs in the context of artificial in ...

that include coupled oscillators (e.g."Oscillatory Networks") are used to solve the

of cognitive neuroscience in perceptual cognition ("feature binding") and in language cognition ("variable binding").

Human movement

Synchronization of movement is defined as similar movements between two or more people who are temporally aligned. This is different from mimicry, which occurs after a short delay.

Line dance A line dance is a choreographed dance in which a group of people dance along to a repeating sequence of steps while arranged in one or more lines or rows. These lines usually face all in the same direction, or less commonly face each other.Knight, ...

and

military step Military step or march is a regular, ordered and synchronized walking of military formations. History The steady, regular marching step was a marked feature of Roman legions. Vegetius, the author of the only surviving treatise on the Roman Empi ...

are examples.

Muscular bonding Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...

is the idea that moving in time evokes particular emotions. 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, cooperation and trust. In dyads, groups of two people, synchronization has been demonstrated to increase affiliation, self-esteem, compassion and altruistic behaviour and increase rapport. 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. 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. 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. More research is required to separate the effect of intentionality from the beneficial effect of synchrony.

Uses

Synchronization is important in

digital telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...

, video and

digital audio Digital audio is a representation of sound recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is typically encoded as numerical samples in a continuous sequence. For example, in CD audio, sa ...

where streams of sampled data are manipulated. Synchronization of image and sound was an important technical problem in

sound film A sound film is a motion picture with synchronized sound, or sound technologically coupled to image, as opposed to a silent film. The first known public exhibition of projected sound films took place in Paris in 1900, but decades passed before ...

. More sophisticated film, video, and

audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum *Digital audio, representation of sound ...

applications use

time code A timecode (alternatively, time code) is a sequence of numeric codes generated at regular intervals by a timing synchronization system. Timecode is used in video production, show control and other applications which require temporal coordinatio ...

to synchronize audio and video. In movie and television production it is necessary to synchronize video frames from multiple cameras. In addition to enabling basic editing, synchronization can also be used for

3D reconstruction In computer vision and computer graphics, 3D reconstruction is the process of capturing the shape and appearance of real objects. This process can be accomplished either by active or passive methods. If the model is allowed to change its shape i ...

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. In

electric power Electric power is the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt, one joule per second. Standard prefixes apply to watts as with other SI units: thousands, millions and billions o ...

systems,

alternator synchronization In an alternating current electric power system, synchronization is the process of matching the frequency of a generator or other source to a running network. An AC generator cannot deliver power to an electrical grid unless it is running at the sam ...

is required when multiple generators are connected to an electrical grid. Arbiters are needed in digital electronic systems such as

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

s 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 In electronics, metastability is the ability of a digital electronic system to persist for an unbounded time in an unstable equilibrium or metastable state. In digital logic circuits, a digital signal is required to be within certain voltage or ...

Encryption In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can decip ...

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 In photography, flash synchronization or flash sync is the synchronizing the firing of a photographic flash with the opening of the shutter admitting light to photographic film or electronic image sensor. In cameras with mechanical (clockwor ...

synchronizes the

flash Flash, flashes, or FLASH may refer to: Arts, entertainment, and media Fictional aliases * Flash (DC Comics character), several DC Comics superheroes with super speed: ** Flash (Barry Allen) ** Flash (Jay Garrick) ** Wally West, the first Kid ...

with the shutter. Some systems may be only approximately synchronized, or

plesiochronous In telecommunications, a plesiochronous system is one where different parts of the system are almost, but not quite, perfectly synchronised. According to ITU-T standards, a pair of signals are plesiochronous if their significant instants occur at ...

. Some applications require that relative offsets between events be determined. For others, only the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

of the event is important.

Notes

References

External links

* * J. Domańsk
"Mathematical synchronization of image and sound in an animated film"
{{Nonverbal communication Systems