JP7142451B2 - Volume control device and broadcasting system - Google Patents

Description

The present invention relates to a volume control device capable of controlling the volume of audio output from an audio output device and a broadcasting system using the same, and relates to a plurality of volume control devices installed in noisy spaces such as station concourses and platforms (station platforms), for example. The present invention relates to a volume control device and a broadcasting system which are effectively applied to control the volume of sound output from a speaker for each speaker installed at different positions.

Station concourses and station platforms are equipped with speakers for outputting voices (guidance announcements) for announcing passenger guidance information and the like. It is desired that guidance announcements output from such speakers be easy to hear without being affected by ambient noise.
In an environment with a lot of background noise such as a station concourse, there is a problem that the guidance announcement is drowned out by the background noise and is difficult to hear. In addition, since guidance announcements on station platforms were performed at a preset constant volume regardless of day or night, ambient noise was relatively low at night. There was a problem that it gave discomfort to others.

Conventionally, it relates to a control device that detects a noise component contained in collected external sound (synthetic sound of broadcast sound and noise) and determines the gain of volume amplifying means according to the level of this noise component. An invention has been proposed (see Patent Document 1, for example). However, since it is difficult to accurately detect only the noise component from the collected external sound (synthetic sound of broadcast sound and noise), even if the invention of Patent Document 1 is applied, the reproduced sound output from the speaker cannot be detected. There is a problem that the sound volume cannot be set appropriately.
On the other hand, based on the volume of the sound collected by the sound collecting means (microphone) between the output start timing and the output end timing of the silent portion detected by detecting the silent portion from the audio input signal, 2. Description of the Related Art An invention related to a volume control device that controls the volume (reproduction volume) of reproduced sound output from an audio output device (speaker) has been proposed (see, for example, Patent Document 2).

JP-A-5-316598 JP 2015-149551 A

However, in the volume control device described in Patent Document 2, if the broadcast sound continues for a long time, the chances of detecting the noise decrease. There is a problem that it becomes difficult to control
In addition, conventional volume control devices, including those described in Patent Documents 1 and 2, collect and measure external noise with a microphone, and control the playback volume according to the magnitude of the collected noise. Since it is a system that uses microphones, there is a problem that conversations of people in the vicinity of the microphone are picked up, which is not desirable from the viewpoint of privacy protection. Therefore, the present inventors considered using a sound level meter instead of a microphone for measuring external noise. However, when using a sound level meter, it becomes very difficult to distinguish between the sound of the broadcast and the ambient noise.

The present invention has been made in view of the problems described above, and its object is to measure in advance the noise level of the reproduced sound from the broadcast sound, thereby reducing the noise level of the reproduced sound output from the audio output device. To provide a volume control device and a broadcasting system capable of appropriately controlling volume at any time.
Another object of the present invention is to appropriately control the volume of reproduced sound output from an audio output device while protecting privacy by measuring the noise level of noise including broadcast sound using a sound level meter. To provide a volume control device and a broadcasting system capable of

In order to achieve the above object, the present invention
A broadcast sound signal input from a sound source is amplified by a signal amplifier and supplied to an audio output device, and the volume of reproduced audio output from the audio output device is controlled by changing the amplification factor of the signal amplifier. In a volume control device for audio broadcasting in a station concourse or station platform ,
noise level acquisition means for capturing measured values from a sound level meter disposed at a predetermined location where reproduced audio output from the audio output device reaches;
storage means for storing data representing the correlation between the volume of the reproduced sound of the broadcast sound from the sound source and the noise level measured in advance during a quiet time period by the sound level meter;
The environment included in the noise level acquired by the noise level acquisition means by referring to the data stored in the storage means based on the broadcast sound input from the sound source and the amplification factor of the signal amplifier. noise amount estimating means for estimating the level of noise;
The amplification factor of the signal amplifier is adjusted according to the environmental noise level estimated by the noise amount estimating means so that the volume of the reproduced voice has a predetermined signal-to-noise ratio with respect to the estimated environmental noise level. and an amplification factor setting means for setting so as to be
The amplification factor setting means amplifies the signal amplifier so that the level of the reproduced sound output from the audio output device is 8 to 13 dB higher than the environmental noise level estimated by the noise amount estimation means. It is configured to set the rate .

According to the volume control apparatus having the configuration as described above, the noise level of the broadcast sound is measured in advance and stored in the storage means as data showing the correlation. Based on the broadcast sound and the amplification factor of the signal amplifier, the correlation data stored in the storage means is referenced to estimate the level of the environmental noise, and the volume of the sound reproduced by the audio output device (speaker) is estimated. Since the amplification factor of the signal amplifier is set so that the sound volume has a predetermined signal-to-noise ratio for the environmental noise level, there is no need to measure the noise immediately before the start of the broadcast, so the broadcast sound is prolonged. It is possible to appropriately control the volume of the reproduced sound output from the audio output device even when there is no opportunity to detect the environmental noise due to the continuation of the time, or when the environmental noise changes during the broadcast. .
Moreover, since the noise level of the noise including the broadcast sound is measured using the sound level meter, the volume of the reproduced sound output from the audio output device can be appropriately controlled while protecting the privacy. Also, by using a sound level meter, the amount of data is less than that of voice data from a microphone, and the burden on the device is reduced.

Here, preferably, the noise amount estimating means estimates the level of environmental noise by subtracting the noise level based on the broadcast sound input from the sound source from the noise level measured by the sound level meter. .
According to such a configuration, it is possible to relatively accurately estimate the environmental noise level around the installation location of the sound level meter by simple processing.

Further, desirably, the amplification factor setting means is configured to be able to individually set the amplification factors of the plurality of signal amplifiers corresponding to a plurality of audio output devices,
The storage means stores a transmission coefficient related to an attenuation amount of the reproduced sound output from the plurality of sound output devices until it reaches the sound level meter,
The noise amount estimating means calculates a noise level based on the broadcast sound input from the sound source from each reproduction volume of each of the plurality of audio output devices and each transfer coefficient, and the noise level measured by the sound level meter. The environmental noise level is estimated by subtracting the calculated noise level from the above.
By configuring in this way, when a plurality of audio output devices (speakers) are installed in the broadcasting target area and the noise caused by the sounds from the plurality of speakers is measured by a sound level meter, the environmental noise level can be accurately determined. It is possible to appropriately control the volume of the reproduced sound that is estimated and output from the audio output device.

Further, desirably, the amplification factor setting means is configured to set the amplification factor of the signal amplification section so that the volume of the reproduced sound output from the audio output device does not exceed a preset upper limit value. do.
By configuring in this way, the volume of the sound output from the sound output device (speaker) is controlled more appropriately so that the broadcast sound can be easily heard, and the reproduced sound of the speaker becomes loud enough to make the user feel uncomfortable. You will be able to avoid overdoing it.

Further, a broadcasting system according to another invention of the present application includes a volume control device having the configuration as described above, a plurality of audio output devices installed in a predetermined area, and installed at predetermined locations in the predetermined area. and a plurality of signal amplifiers corresponding to the plurality of audio output devices, and the noise level acquisition means is configured to be able to capture measured values from the plurality of sound level meters. It is.
According to the invention as described above, since the noise level of the noise including the broadcast sound is measured using the sound level meter, it is possible to appropriately control the volume of the sound output from the sound output device while protecting privacy. In addition, when multiple audio output devices (speakers) are installed in the broadcast area and the noise from the voices from the multiple speakers is measured by a sound level meter, the level of environmental noise can be accurately estimated and the audio output device It is possible to realize a broadcasting system capable of appropriately controlling the volume of the reproduced sound output from.

Here, desirably, a plurality of sound level meters installed at predetermined locations corresponding to the plurality of audio output devices within the predetermined area,
The noise amount estimating means is configured to estimate the level of environmental noise at the installation location of each sound level meter based on the noise level measured by the plurality of sound level meters,
The amplification factor setting means is configured to set the amplification factor of each of the plurality of signal amplifiers according to the noise amount estimated by the noise amount estimation means.
By configuring as described above, when a plurality of audio output devices (speakers) are installed in the broadcast area, it is possible to output audio with an appropriate volume for each speaker.

According to the present invention, by measuring the noise level of the broadcast sound in advance, it is possible to realize a volume control device and a broadcasting system capable of appropriately controlling the volume of the reproduced sound output from the audio output device at any time. be able to. Also, by measuring the noise level of noise including broadcast sound using a sound level meter, the volume control device can appropriately control the volume of the reproduced sound output from the audio output device while protecting privacy. and a broadcasting system can be realized.

1 is a system configuration diagram showing an embodiment of a suitable broadcasting system to which a volume control device according to the present invention is applied; FIG. 1 is a functional block diagram showing a configuration example of a volume control device that constitutes a broadcasting system according to an embodiment of the present invention; FIG. (A) to (C) are explanatory diagrams showing the basic concept of volume control of broadcast sound by the volume control device of the embodiment. 4 is a flow chart showing an example of a volume control procedure in the volume control device of the embodiment; FIG. 9 is an explanatory diagram showing the concept of volume control in the second embodiment of the broadcasting system of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a volume control device according to the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a system configuration diagram showing a schematic configuration of an embodiment suitable for applying a volume control apparatus according to the present invention to an audio broadcasting system that broadcasts information in a noisy space such as a concourse; FIG. 1 is a functional block diagram functionally showing the configuration of an audio broadcasting system according to an embodiment; FIG.

As shown in FIG. 1, the audio broadcasting system of this embodiment includes a plurality of speakers 11 as audio output devices installed at predetermined intervals on the ceiling or pillars under the roof of a space such as a concourse. , 11, . . . , a plurality of sound level meters 12, 12, . It has a broadcast sound source 13 and a signal amplifier 14 including an amplifier that amplifies (including attenuates) an audio signal from the broadcast sound source 13 and supplies it to speakers 11, 11, . The installation position of the sound level meter 12 is within the range where the sound (reproduced sound) output from the speaker reaches. For example, it is preferably near the speaker. .

Further, the sound broadcasting system of this embodiment receives measured values from the sound level meters 12, 12, . , a volume control device 15 including a control PC (computer) 15A for generating and outputting a control signal for the signal amplifier 14, a communication module 15B, and the like. Transmission of measured values from the sound level meters 12, 12, . . .

The sound level meter 12 is a device that measures the volume of sound at the installed position and outputs the measured value in units such as decibels, and has a sampling frequency sufficiently lower than that of a sound collecting device such as a microphone (for example, 1/1000), it is not possible to obtain information that can restore the content of human conversations, and this makes it difficult to protect the privacy of users when installed in a space where an unspecified number of people come and go, such as a concourse. can. A commercially available general sound level meter can be used as the sound level meter 12 of the audio broadcasting system of the present embodiment.

The signal amplifying unit 14 includes a plurality of output terminals that connect the plurality of speakers 11, 11, . It is configured so that the volume of the reproduced sound output from each can be controlled separately. The signal amplifier 14 may be individual amplifiers provided corresponding to each of the plurality of speakers. That is, the audio broadcasting system of the present embodiment can be constructed by using an audio broadcasting system such as a station in which a plurality of speakers and a plurality of amplifiers corresponding to the respective speakers are already installed.

As shown in FIG. 2, the audio broadcasting system of the present embodiment operates on the basis of a signal (noise level) from a sound level meter 12 and a broadcast sound signal (broadcast sound volume) from a broadcast sound source 13, with a broadcast sound source 13 and a speaker 11. and a volume control device 15 for calculating an amplification factor to be set in an amplifier 14 provided between. The volume control device 15 can be realized by software (volume control program) or the like stored in the control PC.
The volume control device 15 shown in FIG. 2 includes a noise level acquisition unit 51 that acquires the noise level based on the signal from the sound level meter 12, and a previously investigated correlation between the reproduced volume of the speaker 11 and the noise level based on the broadcast sound. A correlation storage unit 52 is provided for storing data (tables or formulas) representing relationships.

In addition, the volume control device 15 reads from the correlation storage unit 52 based on the volume of the broadcast sound being output by the broadcast sound source 13 (broadcast volume) and the noise level being measured acquired by the noise level acquisition unit 51. A noise amount estimation unit 53 for estimating the noise level of only environmental noise excluding the broadcast sound from the noise level using the correlation between the sound volume and the noise level, and an amplification factor supplied to the amplifier 14 based on the estimated noise amount. is provided.

The noise amount estimating unit 53 is provided with volume detection means (for example, an AD conversion circuit) for detecting the volume of the broadcast sound output from the broadcast sound source 13 on the input side, so that the detected volume of the broadcast sound being output and From the amplification factor of the amplifier 14, the noise level to be measured by the sound level meter 12 is read out from the correlation storage unit 52, and subtracted from the noise level acquired by the noise level acquisition unit 51 at that time. level can be estimated. In a system that reproduces only broadcast sound whose volume level is known in advance, the volume of the reproduced sound is calculated (V×G) from the volume level (V) of the broadcast sound and the amplification factor (G) of the amplifier 14. Since it can be calculated, the volume detection means is unnecessary.

In addition, when the broadcast sound source 13 is, for example, a microphone with different input voice volumes, the broadcast sound source 13 can be configured so that the output signal always has a constant volume regardless of the sound volume. The volume detection means on the input side of the volume estimator 53 becomes unnecessary. In the following description, it is assumed that the volume output from the broadcast sound source 13 is constant and that there is no volume detection means.
The amplification factor calculator 54 adjusts the amplification factor G so that the reproduced sound output from the speaker has a volume having a predetermined SN ratio (signal-to-noise ratio) with respect to the amount of noise estimated by the noise amount estimator 53. Calculate and set. Specifically, the amplification factor G of the amplifier 14 is set so that the sound reproduced by the speaker is 8 to 13 dB louder than the estimated noise amount.

The noise level acquisition unit 51 acquires the noise level of only the broadcast sound when examining the correlation, and acquires the noise level of the ambient sound in which the environmental noise is added to the broadcast sound when the actual volume control is performed. get. Specifically, the reproduced sound of the broadcast sound is output from the speaker 11 while changing the amplification factor of the amplifier 14 in a quiet environment in advance, and the noise level measured by the sound level meter 12 at that time is measured by the noise level acquisition unit 51. and stored in the correlation storage unit 52 by examining the correlation between the volume of the reproduced sound (speaker reproduced sound) (broadcast sound volume x amplifier amplification factor) and the obtained measured value of the sound level meter. Generate data representing the correlation.

Next, the basic concept of volume control by the volume control device 15 that constitutes the audio broadcasting system of the above embodiment will be described with reference to FIG.
FIG. 3A is a graph showing an example of the correlation between the reproduced volume of the broadcast sound stored in the correlation storage unit 52 and the noise level (quiet environment broadcast sound noise level) measured by a sound level meter. Table data or equations corresponding to the graph of FIG. 3A are measured and stored in the correlation storage unit 52 for each measurement point, that is, the installation location of the sound level meter 12 .

FIG. 3B is a graph of the total noise measured by the sound level meter 12 acquired by the noise level acquisition unit 51. This graph shows the noise level of the broadcast sound in FIG. environmental noise (hatched part).
The noise amount estimation unit 53 has a function of estimating environmental noise (hatched portion) by subtracting the broadcast sound noise portion of FIG. 3(A) from the graph of FIG. 3(B).

Then, as shown in FIG. 3(C), the amplification factor calculation unit 54 sets the reproduced sound level SL of the speaker to be 8 to 13 dB higher than the noise level NL estimated by the noise amount estimation unit 53. The amplification factor G of the amplifier 14 is set. Further, if the amplification factor G is set such that the reproduced sound level SL of the speaker exceeds the volume upper limit, that is, the maximum allowable volume level LMAX, the amplification factor calculation unit 54 , it has a function of limiting the amplification factor G of the amplifier 14 so as not to exceed the upper limit. As a result, the volume of the reproduced sound output from the speaker 11 is controlled so that the broadcast sound can be easily heard, and the reproduced sound of the speaker can be prevented from becoming too loud to the extent that the station user feels uncomfortable.

Next, a procedure for volume control by the volume control device 15 will be described with reference to the flowchart of FIG. Note that before the volume control according to the flowchart of FIG. It is assumed that data (table or formula) representing the correlation between the reproduced sound volume and the noise level read out from the storage section 52 is created and stored in the correlation storage section 52 .

When the process of FIG. 4 is started, the volume control device 15 gives a command to the broadcast sound source 13 in a state where the amplification factor of the amplifier 14 is fixed to G1, for example, to output a broadcast sound (or a test sound) to the speaker. 11 reproduces broadcast sound (step S1). Subsequently, the volume control device 15 acquires the measured value of the sound level meter 12 (the noise value including the broadcast sound and the environmental noise) by the noise level acquisition unit 51 (step S2). to estimate the noise level of the broadcast sound (step S3). When reproducing a predetermined broadcast sound whose volume level is known in advance, the volume control device 15 calculates the reproduction volume of the speaker from the volume level of the broadcast sound and the amplification factor G1 of the amplifier 14, The noise level of the broadcast sound can be estimated by referring to the correlation storage unit 52 based on this reproduced sound volume.

Next, the volume control device 15 subtracts the noise level of the broadcast sound detected in step S3 from the noise level acquired in step S2 to estimate the noise level corresponding to only environmental noise (step S4).
Subsequently, the amplification factor G of the amplifier 14 that reproduces the broadcast sound at a predetermined SN ratio with respect to the environmental noise is calculated (step S5), and it is determined whether or not the reproduction volume of the speaker 11 exceeds a preset upper limit value. (step S6). If it is determined that the playback volume exceeds the preset upper limit value (Yes), the process proceeds to step S7, corrects the amplification factor G of the amplifier so that the playback volume is equal to or lower than the preset upper limit value, and proceeds to step S8. move on.

On the other hand, if it is determined in step S6 that the reproduction volume does not exceed the preset upper limit value (No), the process proceeds to step S8, and in step S8, the amplifier 14 is driven with the amplification factor calculated in step S5 or S7. A broadcast sound is amplified and output from a speaker 11.例文帳に追加
By executing the volume control according to the procedure as described above, the broadcast sound can be output from the speaker 11 at a volume that makes it easy to hear the content even in a noisy environment.

(Second embodiment)
Next, a second embodiment of the volume control device 15 will be described with reference to FIG.
In the volume control device 15 of the second embodiment, when reproduced sounds from a plurality of speakers enter a plurality of sound level meters arranged in one broadcasting area, the noise at that part is reproduced from the plurality of speakers 11. The sound becomes louder. Therefore, in the volume control apparatus of the first embodiment, if the volume of the reproduced sound from the plurality of speakers 11 is changed, that is, if the amplification factor of the amplifier 14 is changed for each speaker, appropriate volume control cannot be performed. There is a problem. Therefore, the second embodiment is designed to overcome such problems.

Specifically, in the second embodiment, for example, as shown in FIG. 5, three speakers 11A, 11B, and 11C are arranged in one broadcast area, and noise levels corresponding to the speakers 11A, 11B, and 11C are arranged. When a total of 12A, 12B, and 12C are installed, instead of outputting from all three speakers, the broadcast sound is output from any one speaker in order, and the broadcast sound is output to the plurality of sound level meters 12A, 12C. Measured by 12B and 12C, the noise level measured by the sound level meter of interest when output from which speaker at what volume is examined and stored. That is, the transmission coefficients (attenuation factors) c1, c2, and c3 of the broadcast sound from each speaker to each of the sound level meters 12A, 12B, and 12C are also stored in the correlation storage unit 52. FIG.

Here, when the same broadcast sound (volume V0) is output from the three speakers 11A, 11B, and 11C, the noise level N of the broadcast sound measured by the sound level meter 12A corresponds to the speakers 11A, 11B, and 11C. Assuming that the amplification factors of the amplifiers are G1, G2, and G3,
Noise level N=V0×G1×c1+V0×G2×c2+V0×G3×c3
is represented by
Also, when different broadcast sounds (volumes V1, V2, V3) are output from the three speakers 11A, 11B, 11C, and the amplification factors of the corresponding amplifiers are G1, G2, G3,
Noise level N=V1×G1×c1+V2×G2×c2+V3×G3×c3
is represented by

In the second embodiment, when there are a plurality of speakers and the amplification factor of the amplifier corresponding to one of the speakers is set, the noise amount estimating unit 53 determines the output of the broadcast sound from the other speakers. The noise acquired by the noise level acquisition unit 51 in consideration of the change (increase) in the noise level to be measured by the sound level meter when the volume of another speaker is changed from the amplification factor and the transfer coefficient. It is configured to estimate the level of environmental noise by subtracting the volume of the speaker in question and the volume of other speakers from the level.

When performing the above-described control, when setting the volume of each speaker, that is, the amplification factor of the corresponding amplifier, the amplification factor of the other amplifiers is changed. If the volume to be added to the environmental noise is set within a narrow range such as 10 dB±0.5, it may become difficult to uniquely determine the amplification factors of all amplifiers (they may not converge). Therefore, by setting the volume to be added to the environmental noise with a certain range, such as +8 to +13 dB, it is possible to avoid the above-described difficult situation.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, the data (table or formula) representing the correlation between the reproduced sound volume and the noise level is stored in the correlation storage unit 52. If they are the same, data (table or formula) representing the correlation between the amplification factor of the amplifier and the noise level may be stored in the correlation storage unit 52 .

Further, in the above-described embodiments, an audio broadcasting system for a station concourse was given as an example of an effective broadcasting system by applying the present invention. In particular, it can be applied to broadcasting systems installed in airports, construction sites, public facilities, and the like. Moreover, the present invention is not limited to a broadcasting system that outputs sound, and can be applied to a broadcasting system that outputs music.

11 speaker (audio output device)
12 Sound level meter 13 Broadcast sound source (microphone)
14 signal amplification unit 15 volume control device 51 noise level acquisition unit 52 correlation storage unit 53 noise amount estimation unit 54 amplification factor calculation unit (amplification factor setting means)

Claims (6)

A broadcast sound signal input from a sound source is amplified by a signal amplifier and supplied to an audio output device, and the volume of reproduced audio output from the audio output device is controlled by changing the amplification factor of the signal amplifier. In a volume control device for audio broadcasting in a station concourse or station platform ,
noise level acquisition means for capturing measured values from a sound level meter disposed at a predetermined location where reproduced audio output from the audio output device reaches;
storage means for storing data representing the correlation between the volume of the reproduced sound of the broadcast sound from the sound source and the noise level measured in advance during a quiet time period by the sound level meter;
The environment included in the noise level acquired by the noise level acquisition means by referring to the data stored in the storage means based on the broadcast sound input from the sound source and the amplification factor of the signal amplifier. noise amount estimating means for estimating the level of noise;
The amplification factor of the signal amplifier is adjusted according to the environmental noise level estimated by the noise amount estimating means so that the volume of the reproduced voice has a predetermined signal-to-noise ratio with respect to the estimated environmental noise level. and an amplification factor setting means for setting so as to be
The amplification factor setting means amplifies the signal amplifier so that the level of the reproduced sound output from the audio output device is 8 to 13 dB higher than the environmental noise level estimated by the noise amount estimation means. A volume control device characterized by setting a rate . 2. The noise amount estimating means according to claim 1, wherein said noise amount estimation means estimates the level of environmental noise by subtracting the noise level based on the broadcast sound input from said sound source from the noise level measured by said sound level meter. volume control device. The amplification factor setting means is configured to be able to individually set the amplification factors of the plurality of signal amplifiers corresponding to a plurality of audio output devices,
The storage means stores a transmission coefficient related to an attenuation amount of the reproduced sound output from the plurality of sound output devices until it reaches the sound level meter,
The noise amount estimating means calculates a noise level based on the broadcast sound input from the sound source from each reproduction volume of each of the plurality of audio output devices and each transfer coefficient, and the noise level measured by the sound level meter. 3. The volume control apparatus according to claim 2, wherein the level of environmental noise is estimated by subtracting the calculated noise level from . The amplification factor setting means is configured to set the amplification factor of the signal amplification section so that the volume of the reproduced sound output from the audio output device does not exceed a preset upper limit value. 4. The volume control device according to any one of claims 1 to 3. A volume control device according to any one of claims 1 to 4, a plurality of audio output devices installed in a predetermined area, a sound level meter installed at a predetermined location in the predetermined area, and the plurality of sounds. and a plurality of signal amplifiers corresponding to the output device,
The broadcasting system, wherein the noise level acquisition means is configured to be able to acquire the measured value from the sound level meter. A plurality of sound level meters installed at predetermined locations corresponding to the plurality of audio output devices within the predetermined area,
The noise amount estimating means is configured to estimate the level of environmental noise at the installation location of each sound level meter based on the noise level measured by the plurality of sound level meters,
6. The apparatus according to claim 5, wherein said amplification factor setting means is configured to respectively set the amplification factors of said plurality of signal amplifiers according to the noise amount estimated by said noise amount estimation means. Broadcast system as described.

Images