JP2017092901A - Synchronous broadcasting system, and transmitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technique to facilitate analysis of a reception failure in synchronous broadcasting system.SOLUTION: A synchronous broadcasting system 1 includes a distribution device 2 and a plurality of transmission devices 3 and 4. The distribution device 2 distributes audio data which is a digitized audio signal. The transmission devices 3 and 4 acquire the audio data distributed from the distribution device 2 and transmit a radio wave obtained by frequency-modulating a carrier wave of a preset frequency from the audio data. As a result, synchronous broadcasting using the same frequency is performed by radio waves transmitted by the plurality of transmission devices 3 and 4. In addition, the plurality of transmitting devices 3 and 4 transmit a test wave in which the frequency of the carrier wave is changed by a preset offset frequency in a pause period in which the broadcast is paused. However, the offset frequencies are set to mutually different values between the transmission devices whose broadcasting ranges are overlapped with each other.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for reducing reception obstacles in synchronous broadcasting of audio signals.

  2. Description of the Related Art Conventionally, FM synchronous broadcasting is known in which audio broadcast waves of the same program are transmitted from a plurality of transmission stations, and the same frequency-modulated broadcast waves are transmitted. In synchronous broadcasting, each transmitting station has a matching delay in each arriving wave in a receiving area where a plurality of arriving waves coexist, that is, in a receiving area where the DU ratio representing the ratio of the interference wave to the desired wave is near 0 dB. Occurrence of reception failure is prevented by adjusting the transmission timing.

However, in synchronous broadcasting, since the frequencies of the desired wave and the interference wave are the same, it is difficult to separate them at the reception point, which makes it difficult to analyze the reception failure.
In contrast, Patent Document 1 provides a facility for receiving incoming waves at a point where incoming waves from two transmitting stations coexist as a technique for adjusting the transmission timing at the transmitting station according to the situation, It has been proposed to receive signals transmitted from both transmitting stations with a phase difference of 180 degrees and adjust the transmission timing of one transmitting station so that the received signal becomes zero.

JP-A-9-284240

However, in the prior art, it is necessary to install a facility for receiving incoming waves separately from the transmitting station, and there is a problem that the system configuration becomes complicated.
In addition, in the prior art, it is necessary to install the facility in a countermeasure area where the DU ratio is near 0 dB. However, there is a problem that the countermeasure area cannot be specified in the first place.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a technique that facilitates analysis of reception failure in a synchronous broadcasting system.

  The synchronous broadcast system of the present invention includes a distribution device (2) and a plurality of transmission devices (3, 4). The distribution device distributes audio data that is a digitized audio signal. The transmission device acquires the audio data distributed from the distribution device, and transmits a radio wave obtained by frequency-modulating a carrier wave having a preset frequency with the audio data. Thereby, the synchronous broadcasting using the same frequency is implemented by the radio waves transmitted by the plurality of transmission apparatuses. In addition, the plurality of transmission devices transmit, as a test wave, a signal obtained by changing the frequency of the carrier wave by a preset offset frequency during a pause period in which the broadcast is suspended. However, in the transmission apparatuses with overlapping broadcast ranges, the offset frequencies are set to different values.

  According to such a configuration, different offset frequencies are added to the plurality of test waves that are transmitted from each transmission device during the suspension period and received in the area requiring countermeasures. For this reason, these test waves can be separated using existing equipment such as a spectrum analyzer, and information necessary for analysis of reception failures, such as measurement of DU ratio, and measures based on the analysis results are easily implemented. can do.

  The transmission device of the present invention includes an audio data acquisition unit (31), a frequency modulation unit (344), a transmission unit (35), and a local signal generation unit (348), and a synchronous broadcasting system together with the distribution device. Configure. The voice data acquisition unit acquires voice data from the distribution device. The frequency modulation unit frequency modulates a carrier wave having a preset frequency with the audio data acquired by the audio data acquisition unit. The transmission unit transmits the output of the frequency modulation unit as a broadcast wave for synchronous broadcasting. The local signal generation unit changes the frequency of the carrier wave by a preset offset frequency during a pause period in which the supply of audio data to the frequency modulation unit is paused.

According to such a structure, since it functions as a transmission apparatus which constitutes the synchronous broadcasting system of the present invention mentioned above, it can be used suitably when constructing this synchronous broadcasting system.
Note that the reference numerals in parentheses described in this column and in the claims indicate the correspondence with the specific means described in the embodiment described later as one aspect, and the technical scope of the present invention. It is not limited.

It is a block diagram which shows the structure of a synchronous broadcast system. It is explanatory drawing which shows the format of AES / EBU specification. It is a block diagram which shows the structure of a modulation transmission part. It is explanatory drawing which shows the frequency spectrum of the intermediate frequency signal IF which an FM modulation part outputs, (a) shows the case where there exists modulation by audio | speech data, (b) shows the case where it is unmodulated. It is explanatory drawing regarding the setting of an offset frequency. It is explanatory drawing which shows the relationship between an offset frequency and the amplitude of a tone burst signal. It is explanatory drawing which shows that the some test wave received can be isolate | separated on a frequency axis. It is explanatory drawing which shows the waveform on the time-axis of the synthetic wave by the received some test wave, (a) is when there is no delay difference of a desired wave and an interference wave, (b) is when there is a delay difference. Indicates. It is explanatory drawing which shows the waveform on the time axis of the tone burst signal extracted from the received some test wave.

Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings.
[1. System configuration]
A synchronous broadcast system 1 shown in FIG. 1 includes a distribution device 2 and a plurality of transmission devices 3 and 4. The distribution apparatus 2 distributes audio frames in an AES / EBU standard format (hereinafter referred to as “AES / EBU format”) standardized by IEC 60958 or the like to the transmission apparatuses 3 and 4 via each transmission network. The transmission apparatus 3 performs synchronous broadcasting according to the audio signal extracted from the audio frame received via the transmission network A, and the transmission apparatus 4 according to the audio signal extracted from the audio frame received via the transmission network B. In the figure, the transmission apparatuses 3 and 4 are provided, but three or more transmission apparatuses may be provided. The transmission network A and the transmission network B are configured by, for example, a wireless transmission network or an IP transmission network, but are not limited to the wireless transmission network or the IP transmission network.

[2. AES / EBU format]
The AES / EBU format is a format for sequentially transmitting audio data obtained by converting an audio signal into digital data. As shown in FIG. 2, the sub-frame of the minimum unit is composed of 32 bits, 4 bits of preamble, 4 bits of auxiliary data, 20 bits of audio data, each 1 bit validity indication flag (V), It consists of user data (U), channel status (C), and parity bit (P). The auxiliary data is used when the audio data is represented by 24 bits. However, the audio data is stored so that the 27th bit side in the frame is the MSB.

Two subframes constitute one frame, and 192 frames constitute one block.
Two subframes constituting one frame are composed of a channel 1 used for data transmission of the left channel of stereo sound and a channel 2 used for data transmission of the right channel of stereo sound. That is, the frame transmission speed is 64 times the sampling frequency of the audio data. The sampling frequency is selected from 48 kHz, 44.1 kHz, and 32 kHz, for example.

  There are three types of subframe preambles (X, Y, Z). The pattern “Z” is used for the preamble of the subframe located at the head of the block (that is, channel 1), and the pattern “X” is used for the preambles of the other channel 1 subframes. The pattern “Y” is used for the preamble of the subframe of channel 2. By extracting these preambles, the beginning of each subframe can be extracted, and by identifying the preamble pattern, the beginning of the subframe, the beginning of the frame, and the like can be identified.

[3. Distribution device]
Returning to FIG. 1, the distribution device 2 includes an audio frame generation unit 21, a first time information acquisition unit 22, a synchronization information addition unit 23, a distribution unit 24, a transmission device 25, and a transmission device 26. . The distribution device 2 may be realized entirely by hardware, or at least partially includes a semiconductor memory such as a CPU, RAM, ROM, flash memory (hereinafter also referred to as a non-transitional tangible recording medium). You may implement | achieve by the process which a known microcomputer performs. In this case, various functions realized by the microcomputer are realized by the CPU executing a program stored in the non-transitional tangible recording medium.

  The audio frame generation unit 21 acquires an audio signal generated for audio broadcasting, and generates an AES / EBU format audio frame. The acquisition source of the audio signal may be, for example, a studio that creates an audio broadcast program, a server that stores an audio signal of a recorded program, or the like.

  The first time information acquisition unit 22 acquires time information indicating a predetermined standard time. Here, a well-known GPS receiver is used, and as a time information, a 1-second pulse signal (hereinafter referred to as 1PPS) that is a 1-second cycle pulse signal and a GPS time representing the occurrence time of the 1PPS are acquired.

  The synchronization information addition unit 23 adds synchronization information generated based on the time information acquired by the first time information acquisition unit 22 to the audio frame generated by the audio frame generation unit 21. Specifically, the output timing of the audio frame is adjusted so that the head of the block coincides with the timing of the 1-second pulse signal, and at the same time, at least a predetermined number including the beginning of the block that coincides with the timing of the 1-second pulse signal The synchronization information is written using the user data (U) area in the subframe.

  The distribution unit 24 distributes the audio frame to which the synchronization information supplied from the synchronization information adding unit 23 is added to a plurality of audio frames and supplies the audio frames to the transmission device 25 and the transmission device 26, respectively. The transmission device 25 distributes the audio frame to which the synchronization information supplied from the distribution unit 24 is added to the transmission device 3 via the transmission network A. The transmission device 26 distributes the audio frame to which the synchronization information supplied from the distribution unit 24 is added to the transmission device 4 via the transmission network B.

[4. Transmitter]
The transmission device 3 includes an audio data acquisition unit 31, a second time information acquisition unit 32, a delay synchronization unit 33, a modulation transmission unit 34, a transmission unit 35, and an antenna 36. As with the distribution device 2, the transmission device 3 may be entirely realized by hardware, or at least a part of the transmission device 3 may be a semiconductor memory such as a CPU, RAM, ROM, flash memory (hereinafter referred to as non-transitional material). It may be realized by a process executed by a known microcomputer having a recording medium). In this case, various functions realized by the microcomputer are realized by the CPU executing a program stored in the non-transitional tangible recording medium.

  The audio data acquisition unit 31 extracts audio data composed of audio frames to which synchronization information is added from the distribution frame signal distributed from the distribution device 2 via the transmission network A, and supplies the audio data to the delay synchronization unit 33. .

  The second time information acquisition unit 32 is the same as the first time information acquisition unit 22 constituting the distribution device 2, and thus the description thereof is omitted. The second time information acquisition unit 32 supplies the acquired time information to the delay synchronization unit 33 and the modulation transmission unit 34.

  The delay synchronization unit 33 generates synchronization information based on audio data composed of audio frames to which the synchronization information acquired by the audio data acquisition unit 31 is added and time information acquired by the second time information acquisition unit 32. Audio data composed of audio frames is output after delay adjustment so that the head of the added block is delayed by a preset delay time for 1 PPS. This set delay time is set to be longer than the worst value of the transmission delay in the transmission networks A and B used in the synchronous broadcasting system 1.

  The modulation transmission unit 34 modulates a carrier wave having a predetermined frequency using the audio data extracted from the audio frame, and the broadcast wave of the synchronous broadcast is transmitted from the antenna 36 toward the broadcast area covered by the own device via the transmission unit 35. Send. Details thereof will be described later.

  The transmission device 4 includes an audio data acquisition unit 41, a second time information acquisition unit 42, a delay synchronization unit 43, a modulation transmission unit 44, a transmission unit 45, and an antenna 46. The audio data acquisition unit 41 acquires audio data composed of audio frames distributed from the distribution device 2 via the transmission network B and supplies the acquired audio data to the delay synchronization unit 43. The other configurations 42 to 46 have the same configurations as the second time information acquisition unit 32, the delay synchronization unit 33, the modulation transmission unit 34, the transmission unit 45, and the antenna 46 of the transmission device 3, respectively. The description is omitted.

[4-1. Modulation transmitter]
As shown in FIG. 3, the modulation transmission unit 34 includes a selector 341, a pilot signal generation unit 342, a composite signal generation unit 343, a frequency modulation unit 344, a mixer 345, a tone signal generation unit 346, a measurement control unit 347, and a local signal generation. Part 348.

  The tone signal generation unit 346 generates test data at the timing of 1 PPS as shown in FIG. 9 while the permission signal EN from the measurement control unit 347 is at the active level. The test data is digital data obtained by sampling a tone burst signal in which a sine wave of a constant frequency belonging to the audio frequency band continues for a fixed period at the same sampling period as the audio data. Here, as the tone burst signal, a signal having a constant frequency of 1 kHz is continued for 200 ms, and a silence signal is continued for 800 ms and is repeatedly output. Further, the amplitude of the tone burst signal needs to be limited, which will be described later. The constant frequency and duration are not limited to the values exemplified here.

  In accordance with the permission signal EN from the measurement control unit 347, the selector 341 selects the audio data supplied from the delay synchronization unit 33 when the permission signal EN is at the inactive level, and when the permission signal EN is at the active level, the tone signal The test data supplied from the generation unit 346 is selected and supplied to the composite signal generation unit 343.

  The pilot signal generation unit 342 generates a pilot signal having a predetermined frequency (for example, 19 kHz) and supplies the pilot signal to the composite signal generation unit 343. However, this pilot signal is digital data obtained by sampling a sine wave having a predetermined frequency at the same sampling frequency as that of audio data.

  The composite signal generator 343 generates an FM broadcast composite signal based on the audio data or test data supplied from the selector 341 and supplies the FM broadcast composite signal to the FM modulator 344. Note that the composite signal has a pilot signal L + R that is a sum signal of the channel 1 audio signal and the channel 2 audio signal, a pilot signal, and an L-R that is a difference signal between the channel 1 audio signal and the channel 2 audio signal. It is a well-known one generated by synthesizing a signal obtained by AM-modulating a carrier wave having a double frequency. However, when the test data is supplied from the selector 341, the signal represents a monaural sound with no LR component. The composite signal generated by the composite signal generation unit 343 is a signal expressed by digital data. That is, the composite signal generation unit 343 generates a composite signal by calculating digital data. Hereinafter, the output of the composite signal generation unit 343 is referred to as modulation data.

  The FM modulation unit 344 generates an intermediate frequency signal IF by frequency-modulating (that is, FM modulation) the modulation data supplied from the composite signal generation unit 343 using a carrier in the intermediate frequency band, and supplies the intermediate frequency signal IF to the mixer 345. To do. Here, a 10.7 MHz carrier is used as a carrier wave in the intermediate frequency band. When the modulation by the audio data or the test data is applied, the intermediate frequency signal IF has a frequency spectrum spread around the carrier frequency as shown in FIG. In this case, as shown in FIG. 4B, it consists only of the frequency component of the carrier wave.

  Returning to FIG. 3, the mixer 345 mixes the local signal LO supplied from the local signal generation unit 348 with the intermediate frequency signal IF supplied from the FM modulation unit 344, thereby using a frequency band (used in FM radio broadcasting). For example, a broadcast signal RF of 76 MHz to 108 MHz) is generated and supplied to the antenna 35.

  The local signal generation unit 348 generates a local signal LO for converting the intermediate frequency signal IF into the frequency of the channel assigned to the synchronous broadcast. Further, the local signal generation unit 348 generates a local signal L to which an offset frequency is added in accordance with the offset instruction signal OS from the measurement control unit 347. As shown in FIG. 5, the settable offset frequency is 0 Hz, ± 0.5 kHz, ± 1 kHz, or ± 1.5 kHz. These offset frequencies are not limited to this, and are set so that the interval between the offset frequencies is larger than the frequency resolution (for example, 300 Hz) of a commercially available measuring instrument such as a spectrum analyzer within an allowable range. It only has to be.

  Returning to FIG. 3, the measurement control unit 347 sets the permission signal EN to an inactive level during the broadcast period in which broadcasting is performed, and instructs the offset instruction signal OS to add 0 Hz, that is, not add an offset frequency. Set as follows. As a result, the tone signal generation unit 346 stops, the selector 341 selects audio data, and the local signal generation unit 348 generates a local signal LO to which no offset frequency is added. On the other hand, in the pause period in which the broadcast signal is paused, the enable signal EN is set to the active level, and the offset instruction OS is set to instruct to add any one preset offset frequency. Accordingly, the tone signal generation unit 346 generates test data, the selector 341 selects the test data, and the local signal generation unit 348 generates the local signal LO to which the offset frequency is added. However, the offset frequency is set so that the communication devices with overlapping broadcast ranges have different offset frequencies.

  Note that the suspension period may be a so-called broadcast suspension period in which the distribution apparatus 2 stops the distribution of the audio data, or may be a fixed period set in advance regardless of the distribution of the audio data. It is conceivable to determine whether or not it is a suspension period based on a schedule of a suspension period prepared in advance and time information. Further, the measurement control unit 347 may be configured to be able to communicate with a control center (not shown), and the communication may be determined based on the communication period or the suspension period. In this case, the offset frequency may be determined by an instruction from the control center.

  Here, the limitation on the amplitude of the tone burst signal generated by the tone signal generation unit 346 will be described. As shown in FIG. 6, the frequency spectrum of the test wave generated using the test data instead of the voice data has a spread centering on the carrier wave to which the offset frequency is added. The spread of the frequency spectrum increases as the amplitude of the tone burst signal is increased. In addition, when test waves are received from a plurality of communication devices, it is impossible to separate the two if the frequency spectra of the two overlap. Therefore, the amplitude of the tone burst signal is set to such a size that the frequency spectra of the test waves received at the same time do not overlap each other. In FIG. 6, fo is the frequency of the carrier wave, offa is the offset frequency of communication apparatus A, and offb is the offset frequency of communication apparatus B. In addition, it is assumed that the broadcast ranges of the communication devices A and B overlap.

[5. Operation]
In the synchronous broadcasting system 1, the distribution device 2 distributes audio data to the transmission devices 3 and 4 during the broadcast period. Receiving the distribution of the audio data, each of the transmission devices 3 and 4 generates a broadcast wave by FM-modulating the carrier wave with the audio data compensated for the transmission delay in the transmission networks A and B. Synchronous broadcasting is realized by transmitting this broadcast wave at the same timing by all the transmission devices 3 and 4.

  On the other hand, during the suspension period, all the transmission devices 3 and 4 use test data that is a tone burst signal synchronized with 1 PPS instead of the audio data distributed from the distribution device 2, and use this test data, A test wave is generated by FM-modulating the carrier wave to which the offset frequency is added. All the transmission apparatuses 3 and 4 repeatedly transmit this test wave at the same timing. In addition, the offset frequencies are different from each other in the transmission apparatuses having overlapping broadcast ranges.

[6. effect]
According to the embodiment detailed above, the following effects can be obtained.
(6a) According to the synchronous broadcasting system 1, when measurement is performed using a measuring instrument such as a spectrum analyzer in an area where broadcast waves / test waves from a plurality of transmission devices are received, a carrier wave is generated for each test wave. Since the frequencies are different, as shown in FIG. 7, each test wave can be detected separately on the frequency axis, and the reception level can be individually measured. For this reason, the DU ratio can be obtained from the measurement result using one of the test waves as a desired wave and the other as an interference wave.

  (6b) On the time axis, as shown in FIG. 8, it is observed that the signal level of the combined wave of both waves changes in a cycle corresponding to the frequency difference between the desired wave and the interference wave. The maximum value Vmax and the minimum value Vmin are read from the waveform, the signal level D of the desired wave from the expression (1), the signal level U of the interference wave from the expression (2), and the DU ratio expressed in decibels from the expression (3). Can also be requested.

  In FIG. 8, (a) shows a case where there is no delay difference between the desired wave and the interference wave, and (b) shows a case where there is a delay difference between the both. However, the difference between the maximum value Vmax and the minimum value Vmin decreases as the phase difference caused by the delay difference approaches 180 °.

  (6c) In the synchronous broadcasting system 1, since the offset frequency used by each of the transmission devices 3 and 4 is known, if the transmission device that is the transmission source of the desired wave is known, the transmission of the interference wave is performed from the cycle of the synthesized wave. It is also possible to estimate the original transmission device.

  (6d) In the synchronous broadcasting system 1, when the test wave is received simultaneously from a plurality of transmitting apparatuses, the desired wave and the interference wave can be separated. Therefore, as shown in FIG. Waveforms can also be measured individually. As a result, the delay time until the tone burst signal is detected from the timing of 1 PPS which is the transmission timing of the test wave in the transmitters 3 and 4, and thus the transmitters 3 and 3 that are the transmission sources of the desired wave and the interference wave Distances up to 4 can also be determined individually.

  (6e) In the synchronous broadcasting system 1, the DU ratio and the delay time of the desired wave and the interference wave can be individually obtained as described above, so that the reception failure can be easily analyzed. Specifically, it is possible not only to easily identify the countermeasure area where the DU ratio is near 0 dB, but also from the delay time measured in the countermeasure area, the transmission device that has transmitted the desired wave and the interference wave The amount of phase adjustment of the broadcast wave at can be easily obtained.

[7. Other Embodiments]
As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the above-mentioned embodiment, It can implement in various deformation | transformation.

  (7a) In the above embodiment, a signal obtained by FM-modulating a carrier wave with a tone burst signal is transmitted as a test wave. However, an unmodulated carrier wave may be transmitted. In this case, when a plurality of test waves transmitted from different transmitters are received simultaneously, the plurality of test waves can be detected separately, and the DU ratio can be measured based on the detection result. .

  (7b) In the above embodiment, the AES / EBU format is used when the audio data is transmitted. However, the present invention is not limited to this, and it is necessary for synchronization in each of the transmission apparatuses 3 and 4. Any format may be used as long as information can be added.

  (7c) In the above embodiment, when the broadcast signal RF is generated from the baseband signal generated by the composite signal generation unit 343, the FM modulation unit 344 and the mixer 345 are used. However, the present invention is not limited to this. For example, instead of these, a so-called direct modulator that directly converts the baseband signal into the broadcast signal RF without generating the intermediate frequency signal IF may be used.

  (7d) In the above embodiment, time information obtained by receiving a signal from a GPS satellite is used as time information. However, the present invention is not limited to this. For example, it can be obtained by receiving time information obtained by receiving signals from satellites such as the Quasi-Zenith Satellite, or standard radio waves using long waves that transmit time information in Japan standard time used for radio clocks, etc. Time information or the like may be used.

  (7e) The functions of one component in the embodiment may be distributed as a plurality of components, or the functions of a plurality of components may be integrated into one component. Moreover, you may abbreviate | omit a part of structure of the said embodiment. Further, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment. In addition, all the aspects included in the technical idea specified only by the wording described in the claim are embodiment of this invention.

  (7f) In addition to the above-described synchronous broadcasting system and transmission device, various programs such as a program for causing a computer to function as the transmission device, a non-transitional actual recording medium such as a semiconductor memory storing the program, a test wave generation method, etc. The present invention can also be realized in the form of.

  DESCRIPTION OF SYMBOLS 1 ... Synchronous broadcasting system, 2 ... Distribution apparatus, 3, 4 ... Transmission apparatus, 21 ... Audio | voice frame production | generation part, 22 ... Time information acquisition part, 23 ... Synchronization information addition part, 24 ... Distribution part, 25, 26 ... Transmission apparatus , 31, 41 ... audio data acquisition unit, 32, 42 ... time information acquisition unit, 33, 43 ... delay synchronization unit, 34, 44 ... modulation transmission unit, 35, 45 ... transmission unit, 36, 46 ... antenna, 341 ... Selector, 342 ... pilot signal generation unit, 343 ... composite signal generation unit, 344 ... FM modulation unit, 345 ... mixer, 346 ... tone signal generation unit, 347 ... measurement control unit, 348 ... local signal generation unit

Claims (8)

A distribution device (2) for distributing audio data which is a digitized audio signal;
A plurality of transmission devices (3, 4) for acquiring the audio data distributed from the distribution device and transmitting radio waves obtained by frequency-modulating a carrier wave having a preset frequency by the audio data;
In a synchronous broadcasting system that implements synchronous broadcasting using the same frequency by radio waves transmitted by the plurality of transmitting devices,
The plurality of transmission devices, during a pause period in which broadcasting is suspended, change the frequency of the carrier wave by a preset offset frequency and transmit it as a test wave,
The synchronous broadcasting system in which the offset frequency is set to a different value between the transmitting apparatuses having overlapping broadcast ranges. In the synchronous broadcasting system according to claim 1,
The synchronous broadcasting system, wherein the offset frequency is set within an allowable range of a frequency deviation of a transmission frequency. In the synchronous broadcasting system according to claim 1 or 2,
The synchronous broadcasting system, wherein the transmission device sets a period during which the distribution device stops distributing the audio data to the plurality of transmission devices as the suspension period. In the synchronous broadcasting system according to any one of claims 1 to 3,
The transmitter modulates a carrier wave used as the test wave with a tone burst signal in which a sine wave having a constant frequency belonging to a voice frequency band continues for a certain period,
The amplitude of the tone burst signal is set such that the frequency spectrum of the test wave transmitted from each of the transmitting devices with overlapping broadcast ranges does not overlap each other. In the synchronous broadcasting system according to claim 4,
The synchronous broadcasting system, wherein the plurality of transmission devices acquire time information representing a predetermined standard time, and modulate the carrier wave by the tone burst signal at every fixed period specified by the time information. A transmission device (3, 4) constituting a synchronous broadcasting system together with a distribution device (2) for distributing audio data which is a digitized audio signal,
An audio data acquisition unit (31) for acquiring the audio data from the distribution device;
A frequency modulation unit (344) for frequency-modulating a carrier wave having a preset frequency with the audio data acquired by the audio data acquisition unit;
A transmission unit (36) for transmitting the output of the frequency modulation unit as a broadcast wave for synchronous broadcasting;
A local signal generation unit (348) having a function of changing the frequency of the carrier wave by a preset offset frequency during a pause period in which the supply of the audio data to the frequency modulation unit is paused;
A transmission apparatus comprising: The transmission device according to claim 6, wherein
A tone signal generation unit (346) that generates a tone burst signal in which a sine wave of a certain frequency belonging to the audio frequency band continues for a certain period;
A selector (341) for supplying a tone burst signal to the frequency modulation unit instead of the audio data during the pause period;
A transmission apparatus comprising: The transmission device according to claim 7, wherein
A time information acquisition unit (32) for acquiring time information representing a predetermined standard time,
The tone signal generation unit generates the tone burst signal at each designated timing with a timing of a certain period specified by the time information as a designated timing.