JP2019176228A - Signal synchronization method - Google Patents

Abstract

To improve synchronization accuracy for a plurality of signals having relatively low correlation without mixing a synchronization signal in the signals.SOLUTION: A signal synchronization method comprises the steps of: acquiring a first target signal (a sound or an image) acquired in a first device; acquiring a synchronization signal (a radio signal or the like) transmitted by a wave faster than a sound wave from a signal source (a radio station or the like) to the first device; acquiring a second target signal (a sound or an image) being a target to synchronize with the first target signal acquired in a second device; acquiring the synchronization signal (the radio signal or the like) transmitted from the signal source to the second device; and synchronizing the first target signal and the second target signal (respective sounds or images) on the basis of cross correlation between the synchronization signal acquired in the first device and the synchronization signal (the radio signal or the like) acquired in the second device.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a technique for synchronizing a plurality of signals.

  A technique for synchronizing various signals such as video or audio is known. Patent Document 1 describes a technique for detecting a timing coincidence point by matching in the time direction between an SD image signal and an HD image signal. Patent Document 2 describes a technique for synchronizing a plurality of performance data with a synchronization signal as a reference for a plurality of performance data in which a musical sound signal and a synchronization signal are superimposed.

Japanese Patent Laid-Open No. 8-70401 JP 2014-153515 A

  The technique described in Patent Document 1 has a problem that it is difficult to synchronize two signals having low correlation. In the technique described in Patent Document 2, there is a problem that the synchronization signal is superimposed on the music signal to be synchronized.

  On the other hand, the present invention provides a technique for improving the synchronization accuracy of a plurality of signals having relatively low correlation without mixing the synchronization signal into the signals.

  The present invention includes a step of acquiring a first target signal acquired in a first device, a step of acquiring a synchronization signal transmitted by a wave earlier than a sound wave from a signal source to the first device, and the first target Acquiring a second target signal that is to be synchronized with a signal and acquired in a second device, acquiring the synchronization signal transmitted from the signal source to the second device, and the first And a step of synchronizing the first target signal and the second target signal based on a cross-correlation of the synchronization signal acquired in the device and the synchronization signal acquired in the second device.

  The synchronization signal may be a signal transmitted by electromagnetic waves.

  The signal synchronization method may include a step of selecting the signal source from a plurality of signal source candidates according to the distance between the first device and the second device.

  The signal synchronization method may include a step of selecting the signal source from a plurality of signal source candidates according to position information of the first device and the second device.

  In the signal synchronization method, a plurality of devices including the first device and the second device are grouped based on a distance between the devices, and the same group among the plurality of grouped devices. For the two devices that belong, the step of selecting using the first signal source among the plurality of signal source candidates as the signal source, and two of the grouped devices belonging to different groups One apparatus may include a step of selecting using a second signal source different from the first signal source among the plurality of signal source candidates as the signal source.

  According to the present invention, it is possible to improve the synchronization accuracy of a plurality of signals having relatively low correlations without mixing the synchronization signals into the signals.

The figure which illustrates the outline | summary of the signal synchronization system 1 which concerns on one Embodiment. 1 is a diagram illustrating a functional configuration of a signal synchronization system 1. FIG. The figure which illustrates the hardware constitutions of the signal synchronizer 10. 3 is a diagram illustrating a functional configuration of the device 20. FIG. FIG. 3 is a diagram illustrating a hardware configuration of the device 20. 4 is a flowchart illustrating an operation of the signal synchronization device 10. The schematic diagram which illustrates the synchronous process which concerns on related technology. The schematic diagram which illustrates the synchronous process which concerns on this embodiment.

1. Configuration FIG. 1 is a diagram illustrating an overview of a signal synchronization system 1 according to an embodiment. The signal synchronization system 1 is a system for synchronizing the signal St [1] and the signal St [2]. The signal St [1] and the signal St [2] are an example of a first target signal and a second target signal that are to be synchronized. The signal St [1] and the signal St [2] are acquired in the device 20 [1] and the device 20 [2], respectively. The device 20 [1] acquires the signal Sr [1] in addition to the signal St [1]. The device 20 [2] acquires the signal Sr [2] in addition to the signal St [2]. The signal Sr [1] and the signal Sr [2] are the same signal transmitted from a common signal source, but what is acquired in the device 20 [1] is referred to as a signal Sr [1], and the device 20 [ 2] is referred to as signal Sr [2]. The signal Sr [1] and the signal Sr [2] are examples of the first synchronization signal and the second synchronization signal, respectively. The signal Sr [1] and the signal Sr [2] are signals that are transmitted from the signal source to the device 20 [1] and the device 20 [2] by waves (for example, electromagnetic waves) earlier than the sound wave. The signal synchronizer 10 receives input of the signal St [1] and the signal Sr [1] from the apparatus 20 [1], and receives input of the signal St [2] and the signal Sr [2] from the apparatus 20 [2]. The signal synchronizer 10 synchronizes the signal St [1] and the signal St [2] based on the cross-correlation between the signal Sr [1] and the signal Sr [2]. When the signals St [1] and St [2] are not distinguished from each other, they are simply expressed as a signal St. The same applies to the signal Sr and the device 20.

  In one example, the signal St [1] and the signal St [2] are signals output from the sensor. The sensor is, for example, a video sensor (imaging device), a sound sensor (microphone), an acceleration sensor, or a temperature sensor. The device 20 [1] and the device 20 [2] are devices on which these sensors are mounted, for example, a smartphone, a camera, or a voice recorder. The signal source is, for example, a WiFi (registered trademark) access point, a radio station, a GPS satellite, the sun, or a mobile phone base station. The signal Sr [1] and the signal Sr [2] are, for example, WiFi (registered trademark) radio waves, radio radio waves, GPS radio waves, sunlight, or radio waves for mobile communication.

  FIG. 2 is a diagram illustrating a functional configuration of the signal synchronization apparatus 10. The signal synchronization device 10 includes an acquisition unit 11, a synchronization unit 12, a storage unit 13, a control unit 14, and a communication unit 15. The acquisition unit 11 acquires the signal St [1] and the signal Sr [1] from the device 20 [1], and acquires the signal St [2] and the signal Sr [2] from the device 20 [2]. The acquisition unit 11 may acquire the signal St [1] and the signal Sr [1] at the same time, or may acquire them at different timings. The same applies to the signal St [2] and the signal Sr [2]. The synchronization unit 12 synchronizes the signal St [1] and the signal St [2] based on the cross-correlation between the signal Sr [1] and the signal Sr [2]. The storage unit 13 stores various data. The control unit 14 performs various controls.

  FIG. 3 is a diagram illustrating a hardware configuration of the signal synchronization apparatus 10. In this example, the signal synchronization device 10 is a computer device having a CPU (Central Processing Unit) 101, a memory 102, a storage 103, and a communication IF 104. The CPU 101 is a control device that performs various calculations according to a program and controls other hardware elements of the signal synchronization device 10. The memory 102 is a main storage device that functions as a work area when the CPU 101 executes processing, and includes, for example, a ROM (Read Only Memory) and a RAM (Random Access Memory). The storage 103 is an auxiliary storage device that stores various data and programs, and includes, for example, an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The communication IF 104 is a device for communicating with other devices in accordance with a predetermined communication standard, and includes, for example, a NIC (Network Interface Card).

  In one example, the signal synchronization apparatus 10 is a server apparatus that operates on a network (for example, the Internet). The storage 103 stores a program (hereinafter “server program”) for causing the computer apparatus to function as the signal synchronization apparatus 10 in the signal synchronization system 1. The CPU 101 reads a server program from the storage 103 and executes processing in the memory 102, whereby the functions shown in FIG. In a state where the CPU 101 is executing the server program, the communication IF 104 is an example of the acquisition unit 11. The CPU 101 is an example of the synchronization unit 12 and the control unit 14. At least one of the memory 102 and the storage 103 is an example of the storage unit 13. The communication IF 104 is an example of the communication unit 15.

  FIG. 4 is a diagram illustrating a functional configuration of the device 20. The apparatus 20 includes a generation unit 21, an acquisition unit 22, a storage unit 23, a transmission unit 24, a UI unit 25, and a control unit 26. The generation unit 21 generates a signal St. The acquisition unit 22 acquires the signal Sr. The storage unit 23 stores various data. The data stored in the storage unit 23 includes data obtained by sampling the signal St and data obtained by sampling the signal Sr. Hereinafter, data obtained by sampling the signal St is referred to as data Dt, and data obtained by sampling the signal Sr is referred to as data Dr. The transmission unit 24 transmits the data Dt and the data Dr to the signal synchronization device 10. The UI unit 25 outputs information to the user of the device 20 and inputs an instruction from the user. The control unit 26 performs various controls.

  FIG. 5 is a diagram illustrating a hardware configuration of the device 20. The device 20 is a computer device having a CPU 201, a memory 202, a storage 203, a mobile communication unit 204, a wireless LAN communication unit 205, a camera 206, a microphone 207, a radio reception unit 208, and a touch screen 209. The CPU 201 is a control device that performs various calculations according to a program and controls other hardware elements of the device 20. The memory 202 is a main storage device that functions as a work area when the CPU 201 executes processing, and includes, for example, a ROM and a RAM. The storage 203 is an auxiliary storage device that stores various data and programs, and includes, for example, an SSD or an HDD. The mobile communication unit 204 is a device for communicating with other devices in accordance with a predetermined mobile communication standard (for example, LTE), and includes, for example, an antenna and a chip set that comply with the communication standard. The wireless LAN communication unit 205 is a device for communicating with other devices in accordance with a predetermined wireless LAN communication standard (for example, WiFi (registered trademark)), and includes, for example, an antenna and a chip set conforming to the communication standard. The camera 206 outputs a video signal obtained by photographing the target. The microphone 207 outputs a sound signal obtained from the target. The camera 206 and the microphone 207 are an example of a sensor that detects a target situation and outputs a signal indicating the result. The radio reception unit 208 receives a radio broadcast. The radio reception unit 208 includes, for example, an antenna, a tuning circuit, a detection circuit, and an output circuit. The touch screen 209 includes a display device (for example, an LCD) that displays information and a touch sensor formed on the display device.

  In this example, the radio reception unit 208 has a function of outputting a signal (radio broadcast radio wave) received by the antenna as it is. To output a signal as it is is to output a signal without performing processing such as tuning and detection in radio broadcasting. This signal is used as the signal Sr. The CPU 201 stores the signal output from the radio reception unit 208 in the memory 202 or the storage 203 as data.

  In one example, the device 20 is a device having a function of accessing a network to which the signal synchronization device 10 is connected, for example, a smartphone. The signal St is a video signal indicating a moving image shot with a smartphone. The storage 203 stores a program (data acquisition program) for causing a computer device to function as the device 20 in the signal synchronization system 1. In a situation where the CPU 201 is executing a data acquisition program, the camera 206 is an example of the generation unit 21. The radio reception unit 208 is an example of the acquisition unit 22. At least one of the memory 202 and the storage 203 is an example of the storage unit 23. The mobile communication unit 204 or the wireless LAN communication unit 205 is an example of the transmission unit 24. The touch screen 209 is an example of the UI unit 25. The CPU 201 is an example of the control unit 26.

  In one example, the device 20 executing the data acquisition program displays a UI screen (not shown) including a recording button on the touch screen 209. The recording button is a UI element for receiving an instruction to start recording. When the user touches a position corresponding to the recording button on the touch screen 209, the CPU 201 starts recording the signal St and the signal Sr. During recording of the signal St and the signal Sr, the device 20 displays a UI screen (not shown) including a stop button on the touch screen. The stop button is a UI element for receiving an instruction to start recording. When the user touches a position corresponding to a stop button on the touch screen 209, the CPU 201 assigns attribute information such as a time stamp to the data Dt and the data Dr obtained by converting the signal St and the signal Sr into data, and stores them in the storage 203. . The storage 203 stores information for specifying the correspondence between the data Dt and the data Dr even when there are a plurality of data Dt and a plurality of data Dr. This information is, for example, an identifier that identifies the data Dt. This identifier is included in the file names of the data Dt and the data Dr. In this example, the CPU 201 starts recording the signal St and the signal Sr at the same time and ends them simultaneously. The timing for recording the signal St and the signal Sr only needs to be known in time, and does not need to be recorded simultaneously.

2. Operation FIG. 6 is a flowchart illustrating the operation (signal synchronization method) of the signal synchronization apparatus 10. Before starting the flow of FIG. 4, the device 20 [1] acquires data Dt [1] and data Dr [1], and the device 20 [2] acquires data Dt [2] and data Dr [2], respectively. It is done. In the following description, a functional element such as the acquisition unit 11 may be described as a subject of processing. This is because a hardware element such as the CPU 101 executing software such as a server program is replaced with another hardware element. This means that the process is executed in cooperation with.

  In step S11, the acquisition unit 11 acquires data Dt [1] from the device 20 [1]. For example, the data Dt [1] is transmitted from the device 20 [1] to the signal synchronization device 10 in response to an event that the user inputs a data transmission instruction in the device 20 [1]. The device 20 [1] adds the attribute information to the data Dt [1] and sends it. The attribute information is information accompanying the data D [1]. The attribute information includes, for example, at least one of an identifier of the device 20, an identifier of the user of the device 20, a description of the subject, a time stamp, and position information (latitude and longitude of the device 20 when the image is captured). . Attribute information is similarly added to other data such as data Dr [2]. In step S12, the acquisition unit 11 acquires data Dr [1] from the device 20 [1]. The data Dr [1] is transmitted from the device 20 [1] to the signal synchronization device 10 triggered by the same event as the data Dt [1], for example. Alternatively, the data Dr [1] may be transmitted from the device 20 [1] to the signal synchronization device 10 triggered by an event different from the data Dt [1]. In this case, the relationship with the data Dt [1] is specified by the identifier included in the attribute information of the data Dr [1]. The storage unit 13 stores data Dt [1] and data Dr [1] acquired by the acquisition unit 11.

  In step S13, the acquisition unit 11 acquires data Dt [2] from the device 20 [2]. In step S14, the acquisition unit 11 acquires data Dr [2] from the device 20 [2]. Details of steps S13 and S14 are the same as steps S11 and S12. The storage unit 13 stores data Dt [2] and data Dr [2] acquired by the acquisition unit 11.

  In step S15, the control unit 14 receives an input of an instruction to synchronize two data (hereinafter referred to as “synchronization instruction”). The data synchronization here means the synchronization of the signal waveform indicated by the data and is synonymous with the signal synchronization. This instruction is input from, for example, a terminal device (not shown; for example, a smartphone or a PC that can access the Internet) that can access the signal synchronization device 10. This instruction includes information specifying data Dt [1] and data Dt [2] to be subjected to synchronization processing.

In step S16, the synchronization unit 12 synchronizes the signal specified by the synchronization instruction. Here, synchronizing the signals means specifying a positional shift (difference) between the two signals in the time domain. In one example, the signal St [1] and the signal St [2] are synchronized based on the cross-correlation of the signal Sr [1] and the signal Sr [2]. Specifically, the synchronization unit 12 calculates a time difference τ that maximizes the absolute value | Cij (τ) | of the cross-correlation Cij (τ) expressed by the following equation (1).
Here, the signal yi is a signal indicated by the data Dr [1], that is, the signal Sr [1], and the signal yj is a signal indicated by the data Dr [2], that is, the signal Sr [2]. Equation (1) is obtained by matching the start point of the signal yi (t) and the start point of the signal yj (t) in the time domain, and then the time difference (shift on the time axis) of the signal yj (t) with respect to the signal yi (t) A numerical string indicating the degree of correlation of the signal waveform between the two using the amount τ as a variable. The time difference τ can be a positive value or a negative value. For example, when the signal Sr [2] is located behind the signal Sr [1] in the time domain, the time difference τ is positive, and the signal Sr [2] is located ahead of the signal Sr [1] in the time domain. The time difference τ is negative. The cross-correlation is not limited to that calculated by the equation (1), and may be calculated by the following equation (2), for example.

  FIG. 7 is a schematic view illustrating synchronization processing according to related technology. In this example, the device 20 [1] and the device 20 [2] are located at geographically separated points. The signal source Src_l of the signal Ss outputs a sound signal. The devices 20 [1] and 20 [2] photograph a common subject from their respective positions. Device 20 [1] starts recording at time t1, and device 20 [2] starts recording at time t2. In this example, the signal St [1] and the signal St [2] are synchronized based on the cross-correlation between the signal Ss [1] and the signal Ss [2]. The signal Ss [1] is a sound signal obtained by the device 20 [1] collecting sound from the sound source by the microphone, and the signal Ss [2] is a sound collected by the device 20 [2] by the microphone. It is a sound signal. Since there is a difference between the speed of light and the speed of sound, when the signals St [1] and St [2] are synchronized based on the cross-correlation between the signals Ss [1] and Ss [2], the signal St [ 1] and the signal St [2] may be shifted. For example, if the distance from the sound source to the device 20 [2] is 340 m farther than the distance from the sound source to the device 20 [1], the same sound reaches the device 20 [2] with a delay of 1 second. On the other hand, since the distance between the device 20 [1] and the device 20 [2] is sufficiently small compared to the speed of light, the device 20 [1] and the device 20 [2] acquire the image of the subject almost simultaneously. In this situation, when the signal St [1] and the signal St [2] are synchronized based on the cross-correlation between the signal Ss [1] and the signal Ss [2], the signal St [2] is more than the signal St [1]. Also deviates from the ideal synchronization state by about 1 second (preceding).

  FIG. 8 is a schematic view illustrating synchronization processing according to this embodiment. In this example, the signal Sr [1] and the signal Sr [2] are signals output from the same signal source Src_t (for example, a radio broadcast station). Since the signal Sr [1] and the signal Sr [2] propagate at the speed of light, the same signal is received at substantially the same time even if the device 20 [1] and the device 20 [2] are separated by, for example, 340 m. If the signal Sr [1] and the signal Sr [2] are used as the synchronization signal, the signal St [1] and the signal St [2] can be more accurately synchronized as compared with the example using the sound signal as the synchronization signal. .

  Refer to FIG. 6 again. In step S17, the control unit 14 generates data Ds indicating a signal Ss obtained by synthesizing the synchronized signal St [1] and the signal St [2]. In step S18, the control unit 14 outputs data Ds. For example, the control unit 14 outputs the data Ds to, for example, the terminal device that has output the synchronization instruction. Alternatively, the control unit 14 may store the data Ds in the storage unit 13.

3. Modifications The present invention is not limited to the above-described embodiments, and various modifications can be made. Hereinafter, some modifications will be described. Two or more of the following modifications may be used in combination.

3-1. Modification 1
The device 20 may receive a plurality of types of signals as candidates for the signal Sr. For example, the apparatus 20 receives AM radio broadcast, FM radio broadcast, and WiFi (registered trademark) signals and stores them as data. The device 20 stores these three types of signals as data as candidates for the signal Sr. The device 20 transmits the data of these three types of signals together with the data Dt to the signal synchronization device 10. The signal synchronizer 10 stores these data. The signal synchronizer 10 selects a signal indicated by at least one of the plurality of data as the signal Sr, and synchronizes the signals St obtained in the two devices 20. That is, it can be said that the operation of the signal synchronizer 10 includes a step of selecting a signal source of the signal Sr from among a plurality of signal source candidates according to the distance between the first device and the second device.

  According to this example, a signal to be used as the signal Sr can be selected from a plurality of candidates according to a situation after the signal St (data Dt) is acquired. For example, consider a case where the device 20 [2] receives only an FM radio broadcast signal as the signal Sr. Specifically, when the device 20 [2] has a function of storing only an FM radio broadcast signal as the signal Sr, the device 20 [2] uses a plurality of types of signals as candidates for the signal Sr. One of the cases where the reception of some signals has failed although it has a function of storing. Even when the device 20 [1] cannot know the status of the device 20 [2], the device 20 [1] stores AM radio broadcast, FM radio broadcast, and WiFi (registered trademark) signals as candidates for the signal Sr. Then, the signal Sr can be selected in accordance with the signal synchronization partner. In the previous example, the signal synchronizer 10 can select an FM radio broadcast signal as the signal Sr.

3-2. Modification 2
When the device 20 [1] and the device 20 [2] receive a plurality of types of signals as the candidates for the signal Sr, the signal synchronization device 10 depends on the distance between the device 20 [1] and the device 20 [2]. A signal used as the signal Sr may be selected. That is, it can be said that the operation of the signal synchronizer 10 includes a step of selecting a signal source of the signal Sr from among a plurality of signal source candidates according to the position information of the first device and the second device. In one example, when the distance between the device 20 [1] and the device 20 [2] is shorter than the threshold value, the signal synchronization device 10 signals a signal having a relatively short reach (for example, WiFi (registered trademark)). When the distance between the device 20 [1] and the device 20 [2] is equal to or greater than the threshold value, a signal having a relatively long reach (for example, FM radio broadcast) is selected as the signal Sr. According to this example, an appropriate signal Sr can be used according to the distance between the device 20 [1] and the device 20 [2]. In this example, the signal synchronizer 10 needs to know the positions of the apparatuses 20 [1] and 20 [2] (specifically, the position at the time when the signal St is acquired). Therefore, the device 20 adds its own position information to the attribute information added to the data Dt. The signal synchronizer 10 refers to this position information to determine the distance between the device 20 [1] and the device 20 [2].

3-3. Modification 3
When the device 20 [1] and the device 20 [2] receive a plurality of types of signals as candidates for the signal Sr, the signal synchronization device 10 has position information of at least one of the device 20 [1] and the device 20 [2]. Depending on, a signal used as the signal Sr may be selected. For example, the signal synchronizer 10 stores a map indicating the geographical distribution of signals to be used as the signal Sr. The signal synchronizer 10 refers to this map and selects a signal corresponding to the position information of the device 20 [1] or the device 20 [2] as the signal Sr.

3-4. Modification 4
When synchronizing the signals St acquired in three or more devices 20, the signal synchronization device 10 may classify (group) the plurality of devices 20 into two or more groups. The grouping is performed based on the distance between the devices 20, for example. More specifically, when the distance between the two devices 20 is equal to or less than the threshold value, the signal synchronization device 10 classifies the two devices 20 into the same group. The signal synchronizer 10 selects which signal is used as the signal Sr from among a plurality of candidates for each group. For example, for the device 20 belonging to the first group, the first signal (for example, FM radio broadcast signal) is selected as the signal Sr, and for the device 20 belonging to the second group different from the first group, the second signal (for example, WiFi ( (Registered trademark) signal) is selected as the signal Sr. That is, the operation of the signal synchronizer 10 includes the step of grouping a plurality of devices including the first device and the second device based on the distance between the devices, and the same group among the grouped devices. For two devices belonging to the group, a step of determining to use the first signal source among the plurality of signal source candidates as the signal source, and two of the grouped devices belonging to different groups It can be said that the apparatus includes a step of determining to use, as a signal source, a second signal source different from the first signal source among the plurality of signal source candidates.

3-5. Other Modifications The hardware configuration for realizing the function of the signal synchronization system 1 is not limited to the one exemplified in the embodiment. The signal synchronization system 1 may have any hardware configuration as long as the required function can be realized. In addition, the correspondence relationship between functions and hardware is not limited to that illustrated in the embodiment. For example, the functions implemented in the signal synchronization apparatus 10 in the embodiment may be distributed and implemented in two or more apparatuses. In addition, at least a part of the functions implemented in the signal synchronization apparatus 10 in the embodiment or the modification may be implemented in the apparatus 20. For example, the device 20 itself may have a function as the signal synchronization device 10. In this case, for example, the device 20 [1] acquires the data Dt [2] and the data Dr [2] from the device 20 [2], and uses the data Dr [1] stored by itself to use the signal St [ 1] and signal St [2] are synchronized.

  The program executed in the signal synchronization apparatus 10 and the apparatus 20 may be provided by a storage medium such as an optical disk, a magnetic disk, or a semiconductor memory, or may be downloaded via a communication line such as the Internet. Further, this program need not include the steps exemplified in the embodiment. Some of these steps may be omitted. Further, the order of some of these steps may be changed.

DESCRIPTION OF SYMBOLS 1 ... Signal synchronization system, 10 ... Signal synchronization apparatus, 11 ... Acquisition part, 12 ... Synchronization part, 13 ... Storage part, 14 ... Control part, 20 ... Apparatus, 21 ... Generation part, 22 ... Acquisition part, 23 ... Storage part , 24 ... transmission unit, 25 ... UI unit, 26 ... control unit, 101 ... CPU, 102 ... memory, 103 ... storage, 104 ... communication IF, 201 ... CPU, 202 ... memory, 203 ... storage, 204 ... mobile communication , 205 ... Wireless LAN communication unit, 206 ... Camera, 207 ... Microphone, 208 ... Radio reception unit, 209 ... Touch screen

Claims (5)

Obtaining a first target signal obtained in the first device;
Obtaining a synchronization signal transmitted by a wave earlier than a sound wave from a signal source to the first device;
Acquiring a second target signal that is a target of synchronization with the first target signal and acquired in a second device;
Obtaining the synchronization signal transmitted from the signal source to the second device;
Synchronizing the first target signal and the second target signal based on a cross-correlation between the synchronization signal acquired in the first device and the synchronization signal acquired in the second device. The signal synchronization method according to claim 1, wherein the synchronization signal is a signal transmitted by electromagnetic waves. The signal synchronization method according to claim 1, further comprising: selecting the signal source from a plurality of signal source candidates according to a distance between the first device and the second device. The signal synchronization method according to claim 1, further comprising a step of selecting the signal source from a plurality of signal source candidates in accordance with position information of the first device and the second device. Grouping a plurality of devices including the first device and the second device based on a distance between each device;
Determining to use a first signal source as the signal source among the plurality of signal source candidates for two devices belonging to the same group among the grouped devices;
For two devices belonging to different groups among the grouped devices, a second signal source different from the first signal source among the plurality of signal source candidates is used as the signal source. The signal synchronization method according to claim 1, further comprising: a step of determining.