JP2016127484A - Radio receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio receiver capable of suppressing discomfort of voice due to an influence of fading.SOLUTION: In the radio receiver for receiving a broadcast radio wave including voice and obtaining a voice signal from a received signal, a microcomputer 16 functions as a fading detection unit for detecting fading on the basis of variation of an S meter indicating a reception level of the broadcast radio wave, and an analog radio signal processing unit 23, when fading is detected, performs processing of soft mute, high cut and audio filter for the voice signal so as to suppress a change in reproduced sound generated due to an influence of the fading.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a radio receiver that receives broadcast radio waves such as analog radio broadcasts.

  Some radio receivers include a weak electric field processing circuit in a signal processing circuit for analog radio broadcasting, and the weak electric field processing circuit performs processing in accordance with the reception state of a selected channel such as mute (for example, Patent Documents). 1).

JP 2011-109378 A

By the way, fading may occur when broadcast radio waves are reflected by the ionosphere in the atmosphere. Fading is a phenomenon that causes the strength of radio waves by strengthening or weakening radio waves due to the action of radio waves reflected by the influence of the ionosphere while the radio waves reach the reception point from the transmission point.
In particular, nighttime AM radio broadcasting is characterized in that broadcast waves are likely to arrive from a distance and fading is likely to occur. When fading occurs, the volume change during reception may be severe and difficult to hear.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a radio receiver capable of suppressing the uncomfortable feeling of sound due to the influence of fading.

  In order to achieve the above object, the present invention provides a fading detection that detects fading based on fluctuations in the reception level of the broadcast radio wave in a radio receiver that receives the broadcast radio wave including sound and obtains the audio signal from the received signal. And a sound correcting unit that performs sound correction for suppressing a change in the reproduced sound caused by the fading when the fading is detected.

  In the above configuration, the sound correction unit may perform soft mute for suppressing a change in volume caused by the fading as the sound correction.

  In the above configuration, the sound correction unit may perform another sound correction process for suppressing a change in reproduced sound due to the influence of the soft mute as the sound correction.

  In the above configuration, the other audio correction processing includes a high cut that lowers a high frequency level of the audio according to the reception level, and an audio filter that adjusts the frequency characteristics of the audio without depending on the reception level. You may make it.

  Further, in the above configuration, the fading detection unit determines the magnitude of the fading amount based on the amount of change in the reception level and the fluctuation period, and the audio correction unit performs fading according to the magnitude of the fading amount. The sound correction setting may be changed so as to suppress the change in the reproduced sound due to the influence.

  In the above configuration, the fading detection unit obtains the cycle of the S meter by the number of times the maximum level is reached when the S meter indicating the reception level is within a predetermined minimum level and maximum level range, If the period is within the fading determination range and the number of times of amplitude that exceeds the period exceeds a predetermined threshold, it may be detected that fading is present.

  Further, in the above configuration, the fading detection unit calculates an average number of times when the number of times of amplitude in the cycle exceeds a predetermined threshold, and determines whether or not the average number of times exceeds a predetermined threshold, The sound correction unit may perform the sound correction when the average number of times exceeds a predetermined threshold.

  Further, in the above configuration, the broadcast radio wave is an analog radio broadcast of a digital radio broadcast and an analog radio broadcast that are simultaneously broadcast, and has a reception function of receiving the digital radio broadcast, and the reception state of the digital radio broadcast If the situation deteriorates, it may be switched to the analog radio broadcast.

  According to the present invention, when fading is detected, the sound correction that suppresses the change in the reproduced sound caused by the fading is performed, so that it is possible to suppress the uncomfortable feeling of the sound due to the fading.

It is a block diagram which shows the structure of the radio receiver which concerns on embodiment of this invention. It is a block diagram which shows the function structure of the analog radio signal processing part of a radio receiver. It is a flowchart which shows operation | movement of a radio receiver. It is the figure which showed the example of a time change of S meter at the time of fading. It is a figure where it uses for description of determination of the magnitude of fading amount. It is a figure which shows the parameter setting for fading typically. FIG. 7A is a diagram illustrating setting of soft mute, FIG. 7A is a diagram illustrating a correction curve, and FIG. 7B is a diagram illustrating a setting value of the correction curve. It is a figure which shows the setting of a high cut, FIG. 8 (A) is a figure which shows a correction curve, FIG.8 (B) shows the setting value of a correction curve. FIG. 9A is a diagram illustrating audio filter settings, FIG. 9A is a diagram illustrating a correction curve, and FIG. 9B is a diagram illustrating a setting value of the correction curve.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a radio receiver 1 according to this embodiment.
The radio receiver 1 is an in-vehicle radio receiver mounted on a vehicle, and is configured as a DRM radio capable of receiving a DRM (Digital Radio Mondiale) type radio broadcast broadcast from a radio broadcast station.
The DRM method is applied to AM (amplitude modulation) radio broadcasting (so-called AM broadcasting), and is particularly applicable to digital radio mainly centering on SW (short wave, 2.3 MHz to 27 MHz), and LW (long wave). / MW (medium wave) / SW band correspondence. In DRM radio, simultaneous broadcasting is performed by broadcasting at a digital broadcasting frequency (digital radio broadcasting) and broadcasting at an analog broadcasting frequency (analog radio broadcasting).

  In general, when a digital radio broadcast is received, sound (radio sound) can be output with stable sound quality. On the other hand, analog radio broadcasts, particularly SW broadcasts, tend to reflect radio waves due to changes in the ionosphere in the atmosphere, and are easily affected by the ionosphere. For this reason, if the strength of the radio wave is generated due to fading, the playback volume of the radio receiver increases or decreases, which causes a sense of discomfort in the sound or a user's discomfort. Particularly in nighttime analog radio broadcasting, broadcast waves are likely to arrive from a distance, and fading is likely to occur.

In DRM radio broadcasting, DRM broadcast signals include data such as alternative frequencies for analog radio broadcasts so that they can be handled when they are out of the service area of digital radio broadcasts or in a reception state. In addition, it is possible to switch to an analog radio broadcast frequency of the affiliated station. If the audio periodically fluctuates due to fading during analog radio broadcasting due to the switching, a difference in audio quality between the digital radio broadcasting and the analog radio broadcasting becomes conspicuous, and the audio is likely to be uncomfortable. Also, when receiving digital radio broadcasts, when passing through a running bridge girder, etc., the electric field suddenly fluctuates and cannot be received, and there may be no sound.
The radio receiver 1 according to the present embodiment is formed in a configuration that can suppress an uncomfortable feeling of sound due to fading.

As shown in FIG. 1, a radio receiver 1 includes a radio tuner unit 11 that can receive digital radio broadcasts and analog radio broadcasts, a signal processing unit 12 that performs various signal processing, and a digital radio broadcast unit. A digital radio decoder unit 13 that performs decoding processing, an audio power amplifier unit 15 that inputs analog radio broadcast and digital radio broadcast audio signals and drives an external speaker 14, a microcomputer 16 that controls each unit, and various types A flash memory 17 for holding data and a display 18 for displaying various information are provided.
The radio tuner unit 11 obtains an RF (Radio Frequensy) signal of the receiving station from the radio wave received by the antenna 21, mixes the RF signal and a signal of a local oscillator (not shown), and is an intermediate frequency signal IF (Intermediate Frequency). ) Signal ("IF" in FIG. 1).

In the signal processing unit 12, the A / D converter 22 performs analog-digital conversion on the reception signal (IF signal) output from the radio tuner unit 11, and the analog radio signal processing in the signal processing unit 12 for the reception signal of the analog radio broadcast. The digital radio broadcast reception signal is output to the digital radio decoder unit 13.
The digital radio decoder unit 13 decodes the received digital radio broadcast reception signal (“digital IF” in FIG. 1) to obtain an audio signal (hereinafter referred to as “digital broadcast audio signal”). In FIG. 1, “SD”) is output to the audio signal processing unit 24 in the signal processing unit 12.
As shown in FIG. 1, the digital radio decoder unit 13 includes a BER detection unit 13A that detects a bit error rate (BER) indicating reception quality, and the microcomputer 16 can monitor the detection result.

The analog radio signal processing unit 23 performs demodulation processing on the received analog radio broadcast reception signal to obtain an analog radio broadcast audio signal, and performs audio processing for improving the sound quality on the audio signal to obtain an audio signal (hereinafter referred to as analog signal). Broadcast audio signal) (“SA” in FIG. 1) is output to the audio signal processing unit 24.
The audio processing for improving the sound quality includes, as will be described later, a soft mute processing that suppresses a volume change caused by a change in reception level, a high cut processing that reduces the high frequency level of the audio, and an audio that adjusts the frequency characteristics of the audio. Audio correction processing such as filter processing is included.
The analog radio signal processing unit 23 includes an S meter detection unit 23A that detects an S meter signal indicating a reception level (reception electric field strength) of analog radio broadcast from an input signal (IF signal) of analog radio broadcast. The microcomputer 16 can monitor the detection result.

  The audio signal processing unit 24 inputs the digital broadcast audio signal SD output from the digital radio decoder unit 13 and the analog broadcast audio signal SA output from the analog radio signal processing unit 23, and inputs predetermined audio signals SD and SA to the audio signal processing unit 24. After performing the audio processing, the signal is output to the D / A converter 25. The D / A converter 25 converts the input audio signals SD and SA from digital to analog and outputs them to the audio power amplifier unit 15. As a result, the audio power amplifier unit 15 outputs audio corresponding to the digital broadcast audio signal SD or audio corresponding to the analog broadcast audio signal SA from the speaker 14.

FIG. 2 is a block diagram showing a functional configuration of the analog radio signal processing unit 23. In FIG. 2, a line indicated by a broken line indicates a communication line with the microcomputer 16.
The analog radio signal processing unit 23 is composed of a DSP (Digital Signal Pocessor), an S meter adjustment unit 31 for adjusting the S meter, an S meter output unit 32, and soft mute parameters (soft mute settings 1 and 2 described later). 3), an attenuator 34 for attenuating the signal level, a high cut setting unit 35 for setting high cut processing parameters (high cut settings 1, 2, 3, etc. described later), and an audio filter Are configured to function as an audio filter setting unit 36 for setting the parameters (audio filter settings 1, 2, 3, etc. described later) and an audio filter unit 37 for adjusting the frequency characteristics of the audio signal.

The S meter adjustment unit 31 performs correction by previously adjusting the S meter indicating the received electric field strength of the receiving broadcast station, and the setting can be performed by the microcomputer 16. The S meter output unit 32 externally outputs the S meter signal output from the S meter adjustment unit 31 so that the microcomputer 16 can acquire the S meter signal. The S meter adjustment unit 31 and the S meter output unit 32 constitute the S meter detection unit 23A of FIG.
Based on an instruction from the microcomputer 16, the soft mute setting unit 33 sets a soft mute parameter for changing the sound volume according to the S meter. The attenuator 34 performs soft mute processing according to the setting of the soft mute setting unit 33.

  Based on an instruction from the microcomputer 16, the high cut setting unit 35 sets a high cut parameter for changing the high frequency characteristics in accordance with the S meter. The audio filter setting unit 36 sets the parameters of the audio filter based on the S meter output so as to change the frequency characteristic of the sound according to the S meter. The audio filter unit 37 performs high cut and audio filter processing according to the settings of the high cut setting unit 35 and the audio filter setting unit 36.

The microcomputer 16 has a CPU, a ROM, a RAM, and peripheral circuits, and functions as a control unit that centrally controls the radio receiver 1. The flash memory 17 stores data such as a control program used by the microcomputer 16 and parameters to be described later for sound correction. Further, the microcomputer 16 can perform a tuning process or the like performed by a known radio receiver by executing a control program stored in the flash memory 17.
Further, the control program includes a control program for detecting fading and a control program for performing sound correction that suppresses uncomfortable sound caused by fading. Subsequently, the operation of the radio receiver 1 will be described.

FIG. 3 is a flowchart showing the operation of the radio receiver 1.
In step S1, the microcomputer 16 determines whether or not the DRM radio broadcast (digital radio broadcast) is being received. If it is being received, the microcomputer 16 proceeds to the process of step S2. When the reception frequency is changed during reception of the broadcast, the process proceeds to step S3.
In step S2, the microcomputer 16 checks the reception state of the digital radio broadcast. Specifically, the microcomputer 16 determines the reception state based on the bit error rate (BER) detected by the BER detection unit 13A (FIG. 1). If the BER is within the threshold range where the reception state is good, the reception is performed. To continue the process of step S21. On the other hand, when the BER is in the threshold range where the reception state is bad, the process proceeds to step S3, and the following process for receiving the analog radio broadcast broadcast by the affiliated digital radio broadcast station is started. To do.

In step S3, the microcomputer 16 performs common setting for analog radio reception. For example, a noise blanker or the like effective for pulse-type noise countermeasures is set, and the noise blanker or the like is performed using the above-described analog radio signal processing unit 23 or a noise blanker circuit (not shown).
Next, the microcomputer 16 performs a receivable station check (step S4), a first fading check (step S5), a time zone check (step S6), and a second fading check (step S7).

  In step S4, the microcomputer 16 determines whether or not the station is a receivable station by determining whether or not the S meter signal is within the threshold range of the receivable level for each receiving station. In step S5, the microcomputer 16 checks which band of LW / MW / SW is a fading check target. This process of checking whether or not it is a fading target is performed based on setting data set in advance using the microcomputer 16. For example, it is possible to shorten the software processing time for receiving the LW / NW by setting only the SW having a relatively large fading influence as a fading check target.

In step S6, the microcomputer 16 checks whether or not it is a fading check target time zone. This check process is also performed based on setting data set in advance using the microcomputer 16 as in step S5. For example, it is possible to set only the night when fading is particularly likely to occur as a fading check target.
In step S7, the microcomputer 16 performs fading detection processing (fading detection processing) based on the S meter.

The fading detection process in step S7 will be described.
FIG. 4 is a diagram showing an example of the time change of the S meter during fading.
The microcomputer 16 acquires the minimum level of the S meter (S meter minimum level), the maximum level of the S meter (S meter maximum level), and the fluctuation period of the S meter (S meter period), and fading based on these information. The presence or absence of is determined. More specifically, as threshold values for determining fading, the threshold value L1 of the S meter minimum level, the threshold value L2 of the S meter maximum level, the threshold value L3 of the S meter period, the threshold value L4 of the number of fluctuations S1 of the S meter, and A threshold value L5 of an average number n2 that satisfies the threshold values L1 to L4 is set in advance. When the level of the S meter is between the threshold values L1 and L2, the microcomputer 16 obtains the S meter cycle by the number of times the maximum level is reached, and the S meter cycle is within the fading determination range defined by the threshold value L3. In addition, when the number of times the S meter swings (number of fluctuations n1) exceeds a certain number set by the threshold L4, it is determined that fading is present.
As a result, it is possible to avoid the case where a short-time fluctuation in the reception level is detected as fading, and fading can be detected with high accuracy.

Furthermore, in this embodiment, in order to determine whether fading continues to some extent, the microcomputer 16 obtains an average number n2 of predetermined times for the number of times that satisfies the threshold values L1 to L4, and the average number n2 is a threshold value. When L5 is exceeded, it is determined that fading is present. Accordingly, when fading continues stably, it can be determined that fading is present, and the determination accuracy of fading can be further increased. In this way, the microcomputer 16 can also function as a fading detection unit that detects fading.
Note that the calculation of the average number of times n2 and the comparison between the average number of times n2 and the threshold value L5 may be omitted, and other fading determination methods may be applied.

In step S7, the fading amount is also determined. This determination will be described later.
If it is determined in step S7 that there is no fading, the microcomputer 16 proceeds to the process of step S8, sets "normal reception parameter setting PA", and performs analog radio reception. In this parameter setting PA, since the noise becomes larger as the weak electric field (S meter is smaller), the sound volume is lowered by the soft mute function and the high frequency is lowered by the high cut function.

On the other hand, if it is determined in step S7 that fading is present, the microcomputer 16 selects “three types of fading parameter settings PB1, PB2, and PB3” either automatically (automatically) or manually (manually). Determine whether. This determination is performed based on setting data set in advance using the microcomputer 16.
In the subsequent step S10, the microcomputer 16 selects one of the parameter settings PB1, PB2, and PB3 according to the amount of fading in the case of Auto (automatic), and the parameter setting PB1, in the case of Manual (manual). A parameter setting designated in advance is selected from PB2 and PB3. Then, one of the selected parameter settings PB1, PB2, and PB3 is set, and analog radio reception is performed (steps S11 to S13).

Further, in the present embodiment, even when DRM radio broadcast (digital radio broadcast) is being received and the reception state is in a good threshold range, the first fading check (step S21), the time zone check (step S22), and the first 2 fading check (step S23).
By performing a fading check during digital radio broadcast reception in this way, it is possible in advance to prevent a situation in which the received electric field strength fluctuates abruptly due to passing through a bridge girder while the digital radio broadcast is being received and no audio is output. Thus, it is possible to execute a response in step S23, which will be described later, at an early stage so that the sound is not interrupted. In addition, the process of these steps S21-S23 is the same as that of said step S5-S7.

If it is determined in step S23 that fading is present and the fading amount is large, the microcomputer 16 performs corresponding processing for suppressing the interruption of the sound (step S24).
As this corresponding process, for example, there are the following first process and second process, and which process is performed is determined based on setting data set in advance using the microcomputer 16.
The first process is a process of automatically switching to an affiliated DRM station based on information held in advance and receiving another DRM radio broadcast (digital radio broadcast). The second process is a notification process that prompts the user to switch to reception of analog radio broadcasts. The notification process may be performed by outputting the notification information from the speaker 14 or displaying the notification information on the display 18. It should be noted that various processes that can suppress voice interruption due to fading are applicable to the first process and the second process.

  On the other hand, if it is determined in step S23 that there is no fading or the fading amount is small, the microcomputer 16 continues to receive the digital radio broadcast (step S25). The above is the operation of the radio receiver 1.

Next, “determination of fading amount” performed in steps S7 and S23 will be described. FIG. 5 is a diagram for explaining the determination of the magnitude of the fading amount.
In the present embodiment, when fading is present, the magnitude of the fading amount is determined based on the combination of the level change of the S meter and the S meter cycle in order to specify the magnitude of the fading amount based on the uncomfortable feeling of the reproduced sound. ing.

  In this case, since the microcomputer 16 has a relatively small level change of the S meter and the S meter cycle is relatively long, the reproduced sound has the least discomfort, so that the fading amount is small under this condition. judge. Further, the microcomputer 16 has the largest discomfort in the reproduced sound when the level change of the S meter is relatively large and the S meter period is relatively short. Therefore, it is determined that the fading amount is large under this condition. To do. Further, when the level change of the S meter is small and the S meter cycle is short, or when the level change of the S meter is large and the S meter cycle is long, it is determined that the fading amount is medium.

FIG. 6 is a diagram schematically illustrating the parameter settings PB1, PB2, and PB3 for fading. Each parameter setting PB1, PB2, PB3 includes a soft mute setting, a high cut setting, and an audio filter setting.
The most effective for fading is soft mute. By using soft mute, it is possible to suppress a change in volume due to fading.
In addition, a high cut and an audio filter are used to correct noise. For example, if you soften the soft mute setting in the direction of lowering the audio output in a weak electric field, the noise will sound tighter, so a high cut will be applied, and by lowering the high range with an audio filter, the noise feeling will be reduced and the sound quality will change. It is possible to suppress and correct the sound quality to be easy to hear. Thereby, the sound quality change by the influence of the soft mute at the time of fading can be suppressed by the high cut and the audio filter.

  As shown in the figure, the parameter setting PB1 used when the fading amount is small (fading is small in FIG. 6) includes soft mute setting 1, high cut setting 1, and audio filter setting 1. The parameter setting PB2 used when the fading amount is medium (in FIG. 6, during fading) includes a soft mute setting 2, a high cut setting 2, and an audio filter setting 2. The parameter setting PB3 used when the fading amount is large (fading is large in FIG. 6) includes a soft mute setting 3, a high cut setting 3, and an audio filter setting 3.

The soft mute, high cut, and audio filter settings will be described below. 7A and 7B are diagrams showing soft mute settings. FIG. 7A shows a correction curve, and FIG. 7B shows a set value of the correction curve.
Soft mute is used as a function to reduce the sound output and reduce the volume when the level of the S meter is lowered. Soft mute setting 1 used for parameter setting PA for normal reception and parameter settings PB1, PB2, and PB3 for fading There are two, three.
As shown in FIG. 7A, in the parameter setting PA for normal reception, there is no volume change when it is larger than the medium electric field (value 20), and the volume change becomes large when the electric field fluctuates below the medium electric field. For this parameter setting PA, soft mute setting 1 is set to a correction curve that suppresses volume change, soft mute setting 2 is set to a correction curve that suppresses volume change more than soft mute setting 1, and soft mute setting 3 is soft mute It is set to a correction curve that suppresses volume change more than setting 2.

As shown in FIG. 7B, these correction curves can be set by the operation start position A, the operation end position B, and the attenuation amount C. FIG. 7A shows the operation start position A, the operation end position B, and the attenuation amount C of the parameter setting PA.
That is, as the parameter setting PA changes to the soft mute settings 1, 2, and 3, the volume change is further suppressed.
For this reason, for example, when the S meter fluctuates in the range of 10 to 20, a large volume change indicated by the symbol fa occurs in the parameter setting PA, whereas a small volume indicated by the symbol fb occurs in the soft mute setting 3. The change is sufficient, and the volume change due to the influence of the fluctuation of the S meter can be reduced.

FIG. 8 is a diagram showing the setting of the high cut, FIG. 8A shows the correction curve, and FIG. 8B shows the setting value of the correction curve.
The high cut is used as a function of reducing the noise by cutting the high range when the level of the S meter is lowered. The high cut setting 1 used for the parameter setting PA for normal reception and the parameter settings PB1, PB2, and PB3 for fading. There are two, three.
In the high cut, a correction curve is set for each high frequency (1 kHz, 4 kHz, etc.), and the correction curve is set so that the higher frequency is attenuated. FIG. 8A shows a 4 kHz correction curve as a representative characteristic. The 4 kHz correction curve is a correction curve that lowers the audio output level compared to the 1 kHz correction curve. As the normal reception parameter setting PA changes to the high cut settings 1, 2, and 3, the high frequency audio output level increases. suppress.

As shown in FIG. 8B, the high-cut correction curve can be set by the operation start position A and the operation end position B for each cutoff frequency. FIG. 8A shows an operation start position A and an operation end position B of the parameter setting PA.
In this embodiment, as the parameter setting PA is changed to the high cut settings 1, 2, and 3, the operation start position A and the operation end position B are shifted to the strong electric field side, thereby further suppressing the high-frequency sound output level. Correction characteristics are obtained.
As a result, the volume change is suppressed as the parameter setting PA is changed to the soft mute settings 1, 2, and 3, so that the noticeable noise can be further suppressed, and the sound quality can be corrected to suppress the noise feeling.

FIG. 9 is a diagram showing audio filter settings. FIG. 9A shows a correction curve, and FIG. 9B shows a set value of the correction curve.
The audio filter is used as a fixed filter that changes the sound quality by changing the frequency characteristic of the sound without depending on the S meter, and is used in the parameter setting PA for normal reception and the parameter settings PB1, PB2, and PB3 for fading. There are audio filter settings 1, 2, and 3.
As shown in FIG. 9A, the audio filter has a correction curve for correcting the frequency characteristics to attenuate the high frequency band, and changes to the parameter setting PA for normal reception or the audio filter settings 1, 2, and 3, Reduce the high frequency sound output level.

As shown in FIG. 9B, the correction curve of the audio filter can be set by the cutoff frequency f. FIG. 9A shows the cutoff frequency f of the parameter setting PA.
In this embodiment, the cut-off frequency f is lowered as the parameter setting PA changes to the audio filter settings 1, 2, and 3, thereby obtaining a correction characteristic that further suppresses high-frequency sound output without depending on the S meter. Yes.
As a result, the volume change is suppressed as the parameter setting PA is changed to the soft mute settings 1, 2, and 3, so that conspicuous noise can be suppressed and the sound quality can be corrected with a reduced noise feeling.

  For soft mute and high cut, the time constant setting is also included. By setting this time constant, the attack time (the time it takes for the set curve to complete when the received electric field strength decreases), You can adjust the recovery time (the time it takes for the set curve to be completed, triggered when the received field strength increases). The shorter the time setting is, the more effective it is for noise reduction. However, there is a risk that a change in volume or a change in sound quality will change abruptly and cause a sense of discomfort. The time constant can also be set separately for normal reception and fading.

  As described above, according to the present embodiment, in the radio receiver 1 that receives an analog radio signal that is a broadcast radio wave including sound and obtains an audio signal from the received signal, the microcomputer 16 receives the broadcast radio wave reception level. It functions as a fading detection unit that detects fading based on fluctuations in the S meter, and when the analog radio signal processing unit 23 detects fading, a change in the reproduced sound caused by the fading effect on the audio signal is detected. Since it functions as an audio correction unit that performs audio correction to suppress, it is possible to suppress an uncomfortable feeling of audio due to fading.

  Moreover, since the analog radio signal processing unit 23 performs soft mute for suppressing the volume change accompanying the fluctuation of the S meter as the sound correction, the volume change caused by the fading can be sufficiently suppressed. In addition, the analog radio signal processing unit 23 performs a high cut and an audio filter (another audio correction process) that suppresses a change in the reproduced sound due to the influence of the soft mute as the audio correction, and thus noise that is noticeable due to the influence of the soft mute is removed. It is possible to suppress.

  Moreover, since the high cut that lowers the high frequency level of the sound according to the S meter and the audio filter that adjusts the frequency characteristics of the sound without depending on the S meter are combined, the noise feeling can be reduced efficiently, and listening It becomes easy to correct to easy sound quality. As a result, either volume change due to fading or noise can be reduced, and the sound quality can be corrected.

  Further, the microcomputer 16 determines the magnitude of the fading amount based on the level change of the S meter and the fluctuation cycle, and performs soft mute and high cut so as to suppress the change of the reproduced sound due to the fading effect according to the magnitude of the fading amount Since the setting of the audio filter is changed, it is possible to appropriately suppress the uncomfortable feeling of the voice according to the amount of fading.

  Further, when the S meter indicating the reception level is in the range between the predetermined minimum level (threshold L1) and maximum level (threshold L2), the microcomputer 16 obtains the cycle of the S meter by the number of times the maximum level is reached. When the cycle of the S meter is within the fading determination range (threshold value L3) and the number of times of amplitude (the number of fluctuations n1) exceeds the predetermined threshold value L4, it is detected that fading is present. Fading can be accurately detected based on the level change of the S meter.

  Moreover, the microcomputer 16 obtains the average number n2 when the fluctuation number n1 exceeds a predetermined threshold value L4, determines whether or not the average number n2 exceeds a predetermined threshold value L5, and performs analog radio signal processing. When the average number n2 exceeds a predetermined threshold value L5, the unit 23 performs sound correction for suppressing a change in reproduced sound caused by fading, so that when fading continues, the influence of fading Can reduce the sense of discomfort in the voice.

  In addition, the radio receiver 1 of the present embodiment has a receiving function for receiving digital radio broadcasts and analog radio broadcasts that are simultaneously broadcast. When the reception state of digital radio broadcasts deteriorates, the radio receiver 1 switches to analog radio broadcasts. When switching to broadcasting, it is possible to provide a simulcast-compatible radio receiver capable of suppressing a situation in which a difference in audio quality between digital radio broadcasting and analog radio broadcasting becomes more conspicuous due to fading.

It should be noted that the above-described embodiments are merely illustrative of one embodiment of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention.
For example, in the above-described embodiment, the case where soft mute, high cut, and audio filter processing are performed when fading is detected is described. However, only soft mute, soft mute, Only high cut or soft mute and audio filter processing may be performed. Further, the present invention is not limited to soft mute, high cut, and audio filter audio correction. In short, audio correction that can suppress a change in reproduced sound due to the influence of fading can be widely applied.

  In the embodiment described above, the case where the present invention is applied to the radio receiver 1 of the DRM radio has been described. However, the present invention is not limited to this, and the present invention can be applied to a radio receiver other than the DRM radio. The present invention can be applied to radio receivers that receive AM radio broadcasts. The point is that the present invention can be widely applied to radio receivers that receive broadcast radio waves that include audio and that receive the broadcast radio waves that are influenced by fading and cause changes in the reproduced sound, and obtain audio signals from the received signals.

DESCRIPTION OF SYMBOLS 1 Radio receiver 11 Radio tuner part 12 Signal processing part 13 Digital radio decoder part 14 Speaker 15 Audio power amplifier part 16 Microcomputer (fading detection part)
21 Antenna 23 Analog Radio Signal Processing Unit (Audio Correction Unit)

Claims (8)

In a radio receiver that receives broadcast radio waves including audio and obtains audio signals from the received signals,
A fading detection unit that detects fading based on fluctuations in the reception level of the broadcast radio wave;
A radio receiver comprising: an audio correction unit that performs audio correction for suppressing a change in reproduced sound caused by the fading when the fading is detected.   The radio receiver according to claim 1, wherein the audio correction unit performs soft mute as the audio correction to suppress a volume change caused by the fading.   The radio receiver according to claim 2, wherein the audio correction unit performs another audio correction process for suppressing a change in reproduced sound due to the soft mute as the audio correction.   The other voice correction processing includes a high cut that lowers a high-frequency level of a voice according to the reception level, and an audio filter that adjusts a frequency characteristic of the voice without depending on the reception level. Item 4. The radio receiver according to item 3. The fading detection unit determines the magnitude of the fading amount based on a change amount and a fluctuation period of the reception level,
5. The audio correction unit according to claim 1, wherein the audio correction unit changes the setting of the audio correction so as to suppress a change in reproduced sound due to an influence of fading according to a magnitude of the fading amount. Radio receiver.   The fading detection unit obtains the cycle of the S meter by the number of times the maximum level is reached when the S meter indicating the reception level is within a predetermined minimum level and maximum level range, and the cycle is within the fading determination range. The radio receiver according to claim 1, wherein fading is detected when the number of amplitudes in the cycle exceeds a predetermined threshold. The fading detection unit obtains an average number of times when the number of times of amplitude in the cycle exceeds a predetermined threshold, determines whether or not the average number of times exceeds a predetermined threshold,
The radio receiver according to claim 6, wherein the sound correction unit performs the sound correction when the average number of times exceeds a predetermined threshold. The broadcast radio wave is an analog radio broadcast of a digital radio broadcast and an analog radio broadcast that are simulcast,
A receiving function for receiving the digital radio broadcast;
The radio receiver according to claim 1, wherein when the reception state of the digital radio broadcast deteriorates, the radio radio broadcast is switched to the analog radio broadcast.

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