JP4101719B2 - Audio broadcast receiving apparatus and output sound characteristic control method - Google Patents

Description

  The present invention relates to a technique for improving auditory quality of output sound in an audio broadcast receiving apparatus that receives both an analog audio broadcast and a digital audio broadcast.

  IBOC (In Band on Channel) is known as one method of digital audio broadcasting (for example, Japanese translations of PCT publication No. 2001-520479). IBOC performs digital audio broadcasting using a conventional analog audio broadcasting band such as FM and AM, and a broadcasting station uses this method to execute the same broadcasting program for digital audio broadcasting and analog audio broadcasting. Audio broadcasting called hybrid mode can be performed in which both are broadcast in parallel.

Digital audio broadcasting in IBOC is relatively susceptible to adverse effects due to fading and lack of electric field strength in audio broadcasting receivers due to limitations that must be made using analog audio broadcasting bands.
As a technique for coping with such a problem, an audio broadcast receiver outputs an audio signal received by digital audio broadcast when the reception electric field strength is sufficiently strong, and otherwise by analog audio broadcast. A technique for outputting a received audio signal is known.

Further, as a technique related to an audio broadcast receiver that receives stereo analog audio broadcast, there is also known a technique for reducing noise by degrading the separation characteristics of the right channel and the left channel when the received electric field strength is weak ( For example, Japanese Patent Laid-Open No. 09-036766)
Prior art document information related to the invention of this application includes the following.
JP-T-2001-520479 Japanese Unexamined Patent Publication No. 09-036766

  In the above-described audio broadcast receiving apparatus, according to the technology that automatically switches the audio broadcast that outputs an audio signal between the digital audio broadcast and the analog audio broadcast according to the received electric field strength, at the time of switching, the user can hear There was a problem of giving the discomfort.

  In other words, an audio signal broadcasted by digital audio broadcasting and an audio signal broadcasted by analog audio broadcasting, even if both represent the same object (for example, the same music), both have an audio band and frequency characteristics. Are different from each other. In general, audio signals broadcast in digital audio broadcasts have a wider audio band, and audio signals broadcast in digital audio broadcasts contain higher frequency audio components than audio signals broadcast in analog audio broadcasts. . For this reason, a sudden change in the high-frequency characteristics of the output sound, which occurs when switching between digital audio broadcasting and analog audio broadcasting, gives the user an auditory discomfort. For example, the upper limit of the audio band of an audio signal broadcast by digital audio broadcasting is 20 kHz, the upper limit of the audio band of an audio signal broadcast by analog audio broadcasting is 15 kHz, and the digital audio broadcast and analog are received at a receiving electric field strength of 25 dBμV. If switching to audio broadcasting is performed, when switching from digital audio broadcasting to analog audio broadcasting, an audio component of 15 kHz to 20 kHz is suddenly lost from the output sound as shown in FIG. 10a.

  Also, when switching between digital audio broadcasting and analog audio broadcasting, digital audio broadcasting is usually set to audio broadcasting that outputs audio signals. When the received electric field strength is weak and digital audio broadcasting cannot be received normally, analog audio broadcasting is audio. It is performed so as to be an audio broadcast that outputs a signal. Therefore, when a technique for degrading the channel separation characteristics of the right channel and the left channel when the received electric field strength is weak is applied to reception of analog audio broadcasting, it is high without depending on the received electric field strength as long as data can be normally received. When switching between digital audio broadcasting capable of realizing separation characteristics and analog audio broadcasting, the separation characteristics change suddenly, and this sudden change in the separation characteristics gives an auditory discomfort.

  For example, the relationship between the separation characteristics given to the analog audio broadcast and the received electric field strength is as shown by 1101 in FIG. 10b, and the relationship between the separation characteristics and the received electric field strength when the digital audio broadcast data is normally received. 10b in FIG. 10b, if the received electric field strength is switched between digital audio broadcasting and analog audio broadcasting with the receiving electric field strength of 25 dBμV as a boundary, the digital audio broadcasting is changed from analog to analog audio broadcasting. When switching to audio broadcasting, as shown in FIG. 10c, the separation characteristic of the output sound changes abruptly.

  Therefore, an object of the present invention is not to give a user an unpleasant discomfort when an audio broadcast that outputs an audio signal is automatically switched between a digital audio broadcast and an analog audio broadcast.

  To achieve the above object, an audio broadcast receiving apparatus comprising: a tuner that receives digital audio broadcast and analog audio broadcast in parallel; and an audio output means that outputs an audio signal received by the digital audio broadcast. The monitoring means for monitoring the reception status of the audio broadcast, and the audio output means temporarily when the reception status of the digital audio broadcast monitored by the monitoring means deteriorates from a switching level that is a predetermined level. Broadcast switching means for switching an audio signal to be output from an audio signal received by the digital audio broadcast to an audio signal received by the analog audio broadcast, and according to a reception state of the digital audio broadcast monitored by the monitoring means , By the broadcast switching means Predicting the near future occurrence of switching to the audio signal received by the analog audio broadcast of the audio signal output by the audio output means, and receiving the acoustic characteristics of the audio signal output by the audio output means by the digital audio broadcast Output sound characteristic control means for gradually changing from a first characteristic value determined for the audio signal to be received to a second characteristic value determined for the audio signal received in the analog audio broadcast. is there.

  More specifically, the output audio characteristic control means is, for example, a first level at which the reception state of the digital audio broadcast monitored by the monitoring means is better than the switching level. And the switching state so that the acoustic characteristic of the audio signal output by the audio output means when the reception state becomes the switching level is the second characteristic value. The acoustic characteristic of the audio signal output from the audio output means may be gradually changed from the first characteristic value to the second characteristic value in accordance with the progress of deterioration of the signal.

  According to such an audio broadcast receiving apparatus, it is predicted that a broadcast to be output will be switched to an analog audio broadcast in the near future from the reception state of the digital audio broadcast, and the acoustic characteristics of the output sound are determined as digital audio. The characteristics for broadcasting are gradually changed from those for broadcasting to those for analog audio broadcasting.

Therefore, when actually switching to analog audio broadcasting, the acoustic characteristics of the output sound change close to the acoustic characteristics of analog audio broadcasting. There is no steep change.
That is, for example, the acoustic characteristic is the characteristic of the voice band of the audio signal output from the audio output means, and the upper limit frequency of the voice band based on the first characteristic value is higher than the voice band based on the second characteristic value. If this is the case, the upper limit of the output audio bandwidth when switching to analog audio broadcasting while keeping the upper limit of the output audio bandwidth high when digital audio broadcasting is the target of output is output as an analog audio broadcast In this case, it is possible to suppress the steep change in the output sound band at the time of switching to the analog audio broadcast by changing the upper limit of the sound band of the output sound to near the upper limit.

  Further, if the acoustic characteristic is a channel separation characteristic of an audio signal output from the audio output means, and the first characteristic value is higher than the second characteristic value, the degree of channel separation is higher than the second characteristic value. Output audio channel separation characteristics when outputting analog audio broadcasts when switching to analog audio broadcasts while maintaining a high degree of channel separation of output audio when audio broadcasts are targeted for output It is possible to suppress a sudden change in channel separation characteristics when switching to analog audio broadcasting.

  In these audio broadcast receivers, the broadcast switching means further converts the audio signal output by the audio output means from an audio signal received by the digital audio broadcast to an audio signal received by the analog audio broadcast. After the switching, the audio output when the reception state of the digital audio broadcast monitored by the monitoring unit reaches a return level that is equal to the switching level or a predetermined level that is better than the switching level is a reception state. The audio signal output from the audio signal received by the analog audio broadcast is restored to the audio signal received by the digital audio broadcast. In the output audio characteristic control means, the broadcast switching means includes the audio output means. Output After the audio signal is restored to the audio signal received by the digital audio broadcast, the acoustic characteristic of the audio signal output from the audio output means is gradually changed from the second characteristic value to the first characteristic value. It is also preferable to return to.

By doing so, it is possible to prevent a sudden change in the acoustic characteristics of the output audio even when the analog audio broadcast is returned to the digital audio broadcast.
In order to achieve the above object, the present invention further provides a tuner for receiving digital audio broadcast and analog audio broadcast in parallel to an audio broadcast receiving device, and audio for outputting an audio signal received by the digital audio broadcast. When the output means, the monitoring means for monitoring the reception status of the digital audio broadcast, and the reception status of the digital audio broadcast monitored by the monitoring means are deteriorated from a switching level that is a predetermined level, temporarily The audio signal output by the audio output means is switched from the audio signal received by the digital audio broadcast to the audio signal received by the analog audio broadcast, and the digital audio broadcast monitored by the monitoring means after the changeover. The reception status of Audio signal output by the audio output means when the signal reaches a return level that is equal to a predetermined level or a reception level that is better than the switching level, from the audio signal received by the analog audio broadcast. Broadcast switching means for returning to an audio signal received by an audio broadcast, and the broadcast switching means for returning the audio signal output by the audio output means to an audio signal received by the digital audio broadcast, and then outputting the audio signal. The channel separation characteristic of the audio signal output by the means is determined based on the channel separation characteristic defined for the analog audio broadcast, and the degree of channel separation is higher than the separation characteristic defined for the analog audio broadcast. The channel separation properties defined for digital audio broadcasting is obtained an output sound characteristic control means for progressively changing.

  According to such an audio broadcast receiving apparatus, when the broadcast to be output is switched from the analog audio broadcast to the digital audio broadcast, the channel separation characteristic of the output audio is set to the degree of the channel separation for the analog audio broadcast. The channel separation characteristic is gradually changed from a low channel separation characteristic to a high channel separation characteristic for digital audio broadcasting. Therefore, it is possible to prevent a sudden change in the channel separation characteristics of the output audio when the return from the analog audio broadcast to the digital audio broadcast is performed.

  Here, in these audio broadcast receivers, if the return level is a level in which the reception state is better than the switching level, frequent switching between digital audio broadcasting and analog audio broadcasting due to fluctuations in the reception state. And no return can occur.

  In each of the above audio broadcast receiving apparatuses, the monitoring unit may monitor, for example, the reception intensity of the digital audio broadcast of the tuner as the reception state of the digital audio broadcast.

  As described above, according to the present invention, when an audio broadcast that outputs an audio signal is automatically switched between a digital audio broadcast and an analog audio broadcast, the user is prevented from giving an auditory discomfort. be able to.

Hereinafter, embodiments of the present invention will be described.
First, the first embodiment will be described.
FIG. 1 shows the configuration of an audio broadcast receiving apparatus according to this embodiment.
As shown in the figure, the audio broadcast receiving device includes an operation unit 1, a display device 2, a control unit 3, a tuner 4, an analog broadcast decoder 5, a band filter 6, a digital broadcast decoder 7, a variable band filter 8, a buffer circuit 9, and a digital circuit. An analog converter 10, a selector 11, an amplifier 12, and a speaker 13 are provided.

  The tuner 4 receives the broadcast signal of the reception frequency channel designated from the control unit 3, sends the analog audio signal included in the received broadcast signal to the analog broadcast decoder 5, and the digital audio broadcast signal included in the received broadcast signal. Is sent to the digital broadcast decoder 7. Further, the tuner 4 measures the received electric field strength of the reception frequency channel from the magnitude of the broadcast signal received from the reception frequency channel, and notifies the control unit 3 of it. Note that the audio broadcast that is to be received by the audio broadcast receiving apparatus performs both digital audio broadcast and analog audio broadcast within one frequency channel for the tuner 4.

  The analog broadcast decoder 5 demodulates the analog audio signal from the received analog audio broadcast signal and sends it to the band filter 6. The band-pass filter 6 is, for example, a band-pass filter in which the cutoff frequency fch on the high frequency side is set to 15 kHz and the cutoff frequency fcl on the low frequency side is set to 50 Hz, as shown in FIG. The received analog audio signal is band-limited to an analog audio signal having a voice band between 50 Hz and 15 kHz, and is output to the selector 11 as a first analog audio signal. However, in this embodiment, the audio band of the analog audio signal broadcast by analog audio broadcasting is assumed to be 50 Hz to 15 kHz.

  On the other hand, the digital broadcast decoder 7 decodes the received digital audio broadcast signal to generate a digital audio signal, and sends it to the variable band filter 8. For example, as shown in FIG. 2 b, the variable band filter 8 has a low-frequency cut-off frequency fcl of 50 Hz and a high-frequency cut-off frequency fch variable between 20 kHz and 15 kHz. The cut-off frequency on the high frequency side is set by the control unit 3. The variable band filter 8 limits the received digital audio audio signal to a digital audio signal having an audio band between 50 Hz and the cutoff frequency fch on the high frequency side set at that time, The data is stored in a buffer memory included in the circuit 9. The buffer circuit 9 sequentially outputs the digital audio signal stored in the buffer memory to the digital / analog converter 10 at a predetermined rate. The digital / analog converter 10 converts the received digital audio signal into an analog audio signal, and the second Are output to the selector 11 as analog audio signals. However, in the present embodiment, it is assumed that a substantially reproducible audio band of a digital audio signal broadcast by digital audio broadcasting is 50 Hz to 20 kHz.

  The selector 11 selects either the first analog audio signal input from the bandpass filter 6 or the second analog audio signal input from the digital-analog converter 10 in accordance with the setting of the control unit 3, and sends it to the amplifier 12. The amplifier 12 amplifies the input analog audio signal with the gain set by the control unit 3 and outputs it from the speaker 13.

The control unit 3 performs processing of switching the reception frequency channel received by the tuner 4 according to the operation from the operation unit 1 and various displays on the display device 2.
In addition, the control unit 3 performs a broadcast switching process for switching a broadcast to be output from the speaker 13 between a digital audio broadcast and an analog audio broadcast in accordance with the received electric field strength notified from the tuner 4.
First, the DA switching table and the AD switching table used in the main broadcast switching process will be described.
The DA switching table and the AD switching table are tables set in the control unit 3 in advance, and the DA switching table changes a broadcast to be output from a digital audio broadcast to an analog audio broadcast as the reception electric field strength SM decreases. The relationship between the high-frequency cut-off frequency fch of the variable band filter 8 set before switching to the reception electric field strength SM is defined, and the AD switching table indicates the broadcast to be output as the reception electric field strength SM increases. The high frequency side cut-off frequency fch of the variable band filter 8 set before the switching from the analog audio broadcasting to the digital audio broadcasting and after the switching until the reception electric field strength SM reaches a level sufficient to receive the digital audio broadcasting with a margin. The relationship of the received electric field strength SM is defined.

  That is, in the present embodiment, when Thd> Tha> Thc> Thb, the switching from the digital audio broadcast to the analog audio broadcast as the output target accompanying the decrease in the received electric field strength SM, the received electric field strength SM is Thb. When the reception electric field strength SM exceeds the Thc, the switching from the analog audio broadcast to the digital audio broadcast of the output target broadcast accompanying the increase of the reception electric field strength SM is performed.

  In the DA switching table, as shown in FIG. 3a, the cut-off frequency fch on the high frequency side of the variable band filter 8 is the audio band of the digital audio broadcast when the received electric field strength SM exceeds Tha (50 dbμV in the illustrated example). When Thb (25 dbμV in the example in the figure) <received electric field strength SM ≦ Tha, the cut-off frequency on the high frequency side of the variable band-pass filter 8 decreases as the received electric field strength SM decreases. The relationship that fch gradually decreases from the upper limit frequency (20 kHz) of the audio band of the digital audio broadcast to the upper limit frequency (15 kHz) of the audio band of the analog audio broadcast is an output target as the received electric field strength SM decreases. Switch broadcasting from digital audio broadcasting to analog audio broadcasting ( This is defined as the relationship between the high-frequency cutoff frequency fch and the reception field strength SM before the reception field strength SM becomes equal to or less than Thb.

  On the other hand, in the AD switching table, as shown in FIG. 3b, the cut-off frequency fch on the high frequency side of the variable band filter 8 is the audio band of the analog audio broadcast when the received electric field strength SM is equal to or less than Thc (38 dbμV in the illustrated example). The upper limit frequency (15 kHz in the present embodiment), and when Thc <received electric field strength SM ≦ Thd (63 dbμV in the example in the figure), the cutoff frequency of the high frequency side of the variable band filter 8 increases as the received electric field strength SM increases. The relationship that fch gradually increases from the upper limit frequency (15 kHz) of the audio band of the analog audio broadcast to the upper limit frequency (20 kHz) of the audio band of the digital audio broadcast is an output target as the reception electric field strength SM increases. Switch from analog audio broadcast to digital audio broadcast The high-frequency cutoff frequency fch and the received electric field that are set before and after the switching of the received electric field strength SM to the strength (Thd) sufficient to receive the digital audio broadcast after switching. It is defined as a relationship of strength SM.

Now, the procedure of the broadcast switching process performed by the control unit 3 using such a DA switching table and an AD switching table is shown in FIG.
As shown in the figure, in the broadcast switching process, when the process is started, first, the received electric field strength SM is read from the tuner 4 (step 402), and it is checked whether the received electric field strength SM exceeds Thc (step 404). If so, the high-frequency cut-off frequency fch of the variable band filter 8 is set to the frequency defined in the DA switching table for the received reception field strength SM (step 406). In addition, the selector 11 selects the second analog audio signal from the digital / analog converter 10 to start the output of the digital audio broadcast from the speaker 13 (step 408). After that, until the received electric field strength SM becomes equal to or less than Thb (step 414), the received electric field strength SM is taken from the tuner 4 (step 410), and the high frequency side cut-off frequency fch of the variable band filter 8 is obtained. The received electric field strength SM is set to the frequency defined in the DA switching table (step 412), and the process is repeated. If the received electric field strength SM is equal to or less than Thb (step 414), the selector 11 selects the first analog audio signal from the bandpass filter 6 to output the analog audio broadcast from the speaker 13. Start (step 416) and proceed to step 422.

  On the other hand, if it is determined in step 404 that the received electric field strength SM is equal to or less than Thc, the high frequency side cut-off frequency fch of the variable band filter 8 is set in the AD switching table with respect to the received received electric field strength SM. The frequency is set to a prescribed frequency (step 418), and the selector 11 selects the first analog audio signal from the bandpass filter 6 to start output from the speaker 13 of the analog audio broadcast (step 420). Proceed to step 422.

  In the processing after step 422, the received electric field strength SM is taken in from the tuner 4 (step 422) until the received electric field strength SM exceeds Thc (step 424), and the high frequency side cut-off frequency of the variable band filter 8 is obtained. The process of setting fch to the frequency defined in the AD switching table for the received reception field strength SM is repeated (step 426).

  If the received reception field strength SM exceeds Thc (step 424), the digital audio broadcast is transmitted from the speaker 13 by causing the selector 11 to select the second analog audio signal from the digital-analog converter 10. (Step 428), the high frequency side cut-off frequency fch of the variable bandpass filter 8 is set to the frequency specified in the AD switching table for the received reception field strength SM (step 428). 430).

  Thereafter, the received electric field strength SM is taken in from the tuner 4 (step 438) until the captured received electric field strength SM deteriorates below Thb (step 432) or exceeds Thd (step 434). The high frequency side cutoff frequency fch of 8 is set to the frequency defined in the AD switching table for the received reception field strength SM (step 430), and the process is repeated. If the received reception field strength SM is deteriorated to be equal to or less than Thb (step 432), the selector 11 selects the first analog audio signal from the band filter 6 to output the analog audio broadcast from the speaker 13. Is started (step 436), and the processing returns to step 424. On the other hand, if the received reception field strength SM exceeds Thd (step 434), the process proceeds to step 410, and thereafter, the processing after step 410 described above is performed.

The broadcast switching process performed by the control unit 3 has been described above.
According to such a broadcast switching process, as shown in FIG. 3a, the level of the received electric field strength SM is not expected to change to a level (a level below Thb) at which switching to analog audio broadcasting is performed in the near future. When the signal level changes from a higher level (a level exceeding Tha) to a level for switching to analog audio broadcasting (a level below Thb) because there is a possibility that digital audio broadcasting cannot be normally received, When the intensity SM becomes equal to or less than Tha, the occurrence of switching to the analog audio broadcast of the broadcast to be output in the near future is predicted, and the cut-off frequency fch of the variable frequency filter 8 is set to the digital audio broadcast. When the received electric field strength SM becomes Thb from the upper limit 20 kHz of the voice band, the variable band filter 8 High frequency side cutoff frequency fch is such that the upper limit 15kHz audio band analog audio broadcasting, is progressively changed with the decrease of the reception field strength SM.

  Therefore, when the reception electric field strength SM is actually switched to Thb or lower and switching to analog audio broadcasting is performed, the output audio band changes to the upper limit of 15 kHz of the audio band of analog audio broadcasting. The output audio band does not change steeply even if it is performed.

  Similarly, as shown in FIG. 3b, the reception electric field strength SM increases from the state in which the analog audio broadcast is output because the reception electric field strength SM is at a level where the digital audio broadcast cannot be normally received (a level below Thb). When the received electric field strength SM exceeds Thc> Thb, the broadcast to be output is switched from the analog audio broadcast to the digital audio broadcast, and then the high frequency of the variable band filter 8 is changed. The side cut-off frequency fch is gradually changed from the upper limit 15 kHz of the audio band of analog audio broadcasting to the upper limit 20 kHz of the audio band of digital audio broadcasting as the reception electric field strength SM increases.

  Therefore, after the received electric field strength SM exceeds Thc and switching to digital audio broadcasting is performed, the output audio band gradually changes from the upper limit 15 kHz of the analog audio broadcast audio band to the upper limit 20 kHz. There is no steep change in the output audio band at the time of switching.

  Note that the reception electric field strength level Thc for switching from analog audio broadcasting to digital audio broadcasting is set to a level higher than the reception electric field strength level Thb for switching from digital audio broadcasting to analog audio broadcasting. Is set to the same level to eliminate frequent switching between digital audio broadcasting and analog audio broadcasting when the received electric field strength SM continues to fluctuate in the vicinity of the level. .

  Therefore, when other means are used to cope with such fluctuations in the received electric field strength SM in the vicinity of the level, the received electric field strength SM is uniquely variable according to the switching table shown in FIG. 3c. The high frequency side cut-off frequency fch of the band filter 8 may be determined, and switching between digital audio broadcasting and analog audio broadcasting may be performed always with Thb as a boundary.

The first embodiment of the present invention has been described above.
In the first embodiment described above, during the digital audio broadcast, the switching from the received electric field strength SM to the analog audio broadcast of the target for the output in the near future is predicted. You may make it perform according to other measured values, such as the transmission error incidence rate of the digital audio signal received by audio broadcasting. Also, switching between digital audio digital broadcasting and analog audio broadcasting may be performed according to other measured values such as a transmission error occurrence rate of a digital audio signal received by such digital audio broadcasting.

  Further, in the above, by defining the high frequency side cut-off frequency fch of the variable band filter 8 with respect to the received electric field strength, the gradual change of the output audio band at the time of switching between the digital audio broadcast and the analog audio broadcast is achieved. Although realized, such a gradual change of the output audio band may be realized by changing the cut-off frequency fch on the high frequency side of the variable band filter 8 over time. That is, for example, in an environment where the received electric field strength SM increases or decreases uniformly, when the output is switched from analog audio broadcasting to digital audio broadcasting, it takes a certain time (for example, 2 seconds) after switching, When the high-frequency cut-off frequency fch of the variable band filter 8 is gradually increased or when switching from digital audio broadcasting to analog audio broadcasting is predicted in the near future, a certain time after prediction (for example, 2 seconds) The cut-off frequency fch on the high frequency side of the variable band filter 8 may be gradually reduced until switching to analog audio broadcasting occurs.

Hereinafter, a second embodiment of the present invention will be described.
FIG. 5 shows the configuration of the audio broadcast receiving apparatus according to this embodiment.
As shown in the figure, the audio broadcast receiving apparatus includes an operation unit 1, a display device 2, a control unit 3, a tuner 4, an analog broadcast decoder 5, a frequency filter 501, a digital broadcast decoder 7, a variable frequency filter 502, a buffer circuit 9, and a digital circuit. An analog converter 10, a selector 11, a channel mixer 503, an amplifier 12, a speaker 13, an analog audio peak detector 504, and a digital audio peak detector 505 are provided. That is, the audio broadcast receiving apparatus according to the second embodiment has a frequency filter 501 and a variable frequency filter instead of the band filter 6 and the variable band filter 8 of the audio broadcast receiving apparatus according to the first embodiment shown in FIG. 502, and the audio broadcast receiving apparatus according to the first embodiment shown in FIG. 1 has a configuration in which a channel mixer 503, an analog audio peak detector 504, and a digital audio peak detector 505 are provided.

  The analog broadcast decoder 5 includes an analog channel mixer 506. The analog channel mixer 506 mixes the demodulated right channel audio signal and the demodulated left channel audio signal according to the received electric field strength SM detected by the tuner 4. Thus, the separation characteristics of the output right channel audio signal and the left channel audio signal are controlled as indicated by 1101 in FIG. 10b. That is, as shown in the figure, the analog channel mixer 506 performs a process of reducing noise of an audio signal received by analog audio broadcasting by degrading the channel separation characteristics of the right channel and the left channel when the reception electric field strength SM is weak. Do.

  Next, the analog audio peak detector 504 and the digital audio peak detector 505 receive the peak of the intensity of the audio signal received by the analog audio broadcast input to the selector 11 and the digital audio broadcast input to the selector 11, respectively. A process of detecting the peak of the intensity of the audio signal and notifying the controller 3 is performed. Then, the control unit 3 switches between the digital audio broadcast of the broadcast to be output and the analog audio broadcast according to each peak value input from the analog audio peak detector 504 and the digital audio peak detector 505, The gain of the amplifier 12 is changed so that the peak of the audio signal output to the speaker 13 is the same before and after switching, or is not changed significantly.

  Now, the control unit 3 applies the output from the speaker 13 in accordance with the reception state of the digital audio broadcast obtained from the received electric field strength SM notified from the tuner 4 and the transmission error occurrence rate of the digital audio signal received by the digital audio broadcast. The process of switching between the digital audio broadcast and the analog audio broadcast and the process of predicting the switching of the broadcast to be output from the digital audio broadcast to the analog audio broadcast are performed. This switching and prediction are performed in the same manner as the switching and prediction operations of the first embodiment, for example. Note that the control unit 3 does not perform this switching or prediction for the frequency channel broadcasting only the analog audio broadcast, and unconditionally selects the analog audio broadcast as a broadcast to be output. Similarly, for frequency channels that broadcast only digital audio broadcasts, this switching or prediction is not performed, and digital audio broadcasts are unconditionally selected as broadcasts to be output.

  Next, the frequency filter 501 is a filter having a predetermined frequency response for adjusting the frequency characteristics of the audio signal received from the analog broadcast decoder 5, and the variable frequency filter 502 is the frequency of the audio signal received from the digital broadcast decoder 7. This is a filter with variable frequency response characteristics for adjusting the characteristics. Here, such a variable frequency filter 502 can be configured as an FIR filter in which a plurality of delay elements 601, a plurality of variable gain amplifiers 602, and an adder 603 are combined as shown in FIG. In this case, the control unit 3 controls the frequency response characteristics of the variable frequency filter 502 by changing each tap coefficient (gain of each amplifier 602) of the FIR filter.

  The control unit 3 controls such a variable frequency filter 502, controls the frequency characteristic of the audio signal output to the selector 11, and the frequency characteristic of the audio signal output from the speaker 14 is a broadcast to be output. It is made to change gradually when switching between digital audio broadcasting and analog audio broadcasting. That is, when the broadcast to be output is switched from the analog audio broadcast to the digital audio broadcast, the frequency characteristic of the audio signal output to the selector 11 is changed from the frequency characteristic of the audio signal output from the frequency filter 501 to the digital audio broadcast. The variable frequency filter 502 is controlled so as to gradually change to a predetermined frequency characteristic with respect to the audio signal received from. Also, when switching the broadcast to be output from digital audio broadcast to analog audio broadcast, this switching is predicted in the same manner as in the first embodiment, and the frequency characteristics of the audio signal output to the selector 11 before switching are as follows: The variable frequency filter 502 is controlled so that the frequency characteristic of the audio signal output from the frequency filter 501 gradually changes from the predetermined frequency characteristic of the audio signal received from the digital video broadcast.

Here, the control using the variable frequency filter 502 is the same as the control of the band of the audio signal output from the digital audio broadcast decoder 7 shown in the first embodiment, but the variable frequency filter 502 is changed to the variable band filter 8. The control used as is also included.
Next, the configuration of the channel mixer 503 is shown in FIG. 6b.
As illustrated, the channel mixer 503 includes four amplifiers 651, 652, 653, 654 with variable gain, and two adders 661, 662. Reference numerals 121 and 122 in the figure denote a left channel amplifier 121 and a right channel amplifier 122 included in the amplifier 12, and are connected to the left channel speaker 13 and the right channel speaker 13, respectively.

  The amplifier 651, the amplifier 652, and the adder 661 mix the left channel audio signal and the right channel audio signal input from the selector 11 at a mixing ratio determined by the gain settings of the amplifier 651 and the amplifier 652 of the control unit 3. To the left channel amplifier 12. The amplifier 653, the amplifier 654, and the adder 662 mix the left channel audio signal and the right channel audio signal input from the selector 11 at a mixing ratio determined by the gain settings of the amplifier 653 and the amplifier 654 of the control unit 3. To the right channel amplifier 12.

Therefore, the control unit 3 can adjust the separation characteristics of the left and right channels of the audio signal output from the channel mixer 503 by controlling the gains of the four amplifiers 651, 652, 653, and 654.
Hereinafter, in such an audio broadcast receiving apparatus, in order to prevent a separation characteristic of an output audio signal from changing suddenly when switching between a digital audio broadcast and an analog audio broadcast of an output target broadcast, 3 will be described.

FIG. 7 shows the procedure of the separation characteristic control process.
As shown in the figure, in this process, it is checked whether the broadcast to be output is a digital audio broadcast (step 702). If the broadcast is a digital audio broadcast, the mixing ratio of the main channel of the channel mixer 503 is set to 100%. (Step 704). Here, the mixing ratio of the main channel is the ratio of the right channel audio signal input from the selector 11 included in the right channel audio signal output from the channel mixer 503 for the right channel, and for the left channel, This is the ratio of the left channel audio signal input from the selector 11 included in the left channel audio signal output from the channel mixer 503. Further, the control unit 3 always controls the mixing ratio of the main channel of the right channel and the left channel in the same manner according to the main channel ratio.

  Then, the occurrence of prediction of switching to analog audio broadcasting is monitored (step 706), and if the prediction of switching to analog audio broadcasting occurs, a target ratio is set (step 708). Here, as the target ratio, the same separation characteristic as that of the audio signal expected to be output from the analog broadcast decoder 5 when switching to the analog audio broadcast is given to the audio signal output from the digital audio broadcast decoder 7. Set the main channel ratio. Here, this target ratio is a specific reception electric field strength SM, and when the broadcast to be output is switched from digital audio broadcast to analog audio broadcast, the analog channel mixer 506 performs analog audio broadcast with the specific reception electric field strength SM. Therefore, the same separation characteristic as that given to the audio signal demodulated from the main signal is given to the audio signal output from the digital audio broadcast decoder 7. That is, for example, the separation characteristic that the analog channel mixer 506 gives to the audio signal demodulated from the analog audio broadcast with the received electric field strength SM is a characteristic that outputs the audio signal as a monaural signal, that is, a pair of the left channel and the right channel. In the case of mixing by 1 and outputting as left channel and right channel audio signals, the target ratio is 50%.

  However, when the broadcast to be output is not switched from digital audio broadcast to analog audio broadcast at a specific reception electric field strength SM, for example, the broadcast to be output is converted to digital audio broadcast according to the transmission error rate of the digital audio broadcast. In the case of switching from analog audio broadcasting to analog audio broadcasting, this target ratio is obtained from the digital audio broadcasting decoder 7 with the same separation characteristic as that given to the audio signal demodulated from the analog audio broadcasting by the analog channel mixer 506 with the current received electric field strength SM. You may make it be the main channel ratio given to the audio signal output.

  On the other hand, in general, when the broadcast to be output is switched from digital audio broadcast to analog audio broadcast regardless of whether it depends on the received electric field strength SM or the transmission error rate, it is expected that the received electric field strength is sufficiently low. it can. Therefore, the target ratio here may be uniformly set to 50%.

  If the target ratio is set in this way, it is checked whether or not the current main channel ratio matches the target ratio (step 710). If they match, the process proceeds to step 714. On the other hand, if they do not match, the main channel ratio is increased by one step when the main channel ratio is smaller than the target ratio, and decreased by one step when the main channel ratio is smaller than the target ratio (step 712). . However, the main channel ratio is changed after waiting for a predetermined period of time since the main channel ratio was changed last time. In addition, the magnitude of the step of changing the main channel ratio is based on the prediction of switching to analog audio broadcasting when the one-step main channel ratio is decreased every predetermined period in relation to the predetermined period. It is determined that the main channel ratio decreases to the target ratio in a time (for example, several seconds) that can be expected as the time until switching to the analog audio broadcasting is actually performed. If the main channel ratio is changed by one step in this way, the process proceeds to step 714.

  In step 714, it is checked whether or not switching to analog audio broadcasting has been performed. If switching has been performed, the process proceeds to step 718. If switching has not been performed, the process proceeds to step 716 to switch to analog audio broadcasting. Find out if it is no longer predicted. If it is not predicted, the process proceeds to step 724, and if it is still predicted, the process returns to step 708 to repeat the above processing. As a result, after the switching to the analog audio broadcasting is predicted, the main channel ratio is changed from 100% to the target ratio (targeting time) until the switching to the analog audio broadcasting occurs or no prediction is performed. When the ratio is fixed at 50%, the target ratio is changed toward 50%).

  If it is determined in step 702 that the digital audio broadcast is not currently the output target broadcast, that is, the analog audio broadcast is the output target broadcast, the process proceeds to step 718. In step 718, the main channel ratio is set to 100%, and it waits for the broadcast to be output to be switched to the digital audio broadcast (step 720), and then proceeds to step 722.

  In step 722, as the main channel ratio, the separation characteristic of the audio signal output from the analog broadcast decoder 5 immediately before switching to the digital audio broadcast, that is, the analog channel mixer 506 is set to analog when switching to the digital audio broadcast. The main channel ratio to be given to the audio signal output from the digital audio broadcast decoder 7 having the same separation characteristic as that given to the audio signal demodulated from the audio broadcast is set, and the process proceeds to step 724. In this case, when the broadcast to be output is switched from the analog audio broadcast to the digital audio broadcast when a certain received electric field strength SM is reached, the analog channel mixer 506 uses the received electric field strength SM to perform the analog audio broadcast. The separation characteristics given to the audio signal demodulated from the above are characteristics that output the audio signal as a monaural signal, that is, the left channel and the right channel are mixed one-to-one and output as the left channel and right channel audio signals. In this case, the main channel ratio set in step 722 is 50%.

  Next, in step 724, it is checked whether or not the main channel ratio is 100%. If it is 100%, the process proceeds to step 728. On the other hand, if it is not 100%, the main channel ratio is increased by one level (step 726). However, the main channel ratio is increased after waiting for a predetermined period of time since the main channel ratio was changed last time. Then, the process proceeds to Step 728.

  In step 728, it is checked whether or not a prediction of switching to analog audio broadcasting has occurred. If it has occurred, the process proceeds to step 708 to perform the above-described processing, and if not, the process returns to step 724. As a result, after switching to digital audio broadcasting, the main channel ratio is the main channel ratio that gives the separation characteristics given by the analog channel mixer 506 at the time of switching (the analog channel mixer 506 outputs the audio signal as a monaural signal at the time of switching). If it is predicted that switching to analog audio broadcasting will not occur, it will increase to 100% with a constant time constant.

In the foregoing, the procedure of the separation characteristic control process has been described.
Here, according to such a separation characteristic control process, the main channel ratio of the channel mixer 503 and the separation characteristic of the output audio signal to the speaker 13 are controlled as shown in FIG. 8, for example.
However, in the figure, switching between the digital audio broadcast and the analog audio broadcast of the broadcast to be output is performed according to the received electric field strength SM, and at the time of switching from the digital audio broadcast to the analog audio broadcast The separation characteristics given to the audio signal demodulated from the analog audio broadcast by the analog channel mixer 506 according to the received electric field strength SM at that time are also the same as the received electric field strength SM at the time of switching from the analog audio broadcast to the digital audio broadcast. Accordingly, the separation characteristic that the analog channel mixer 506 gives to the audio signal demodulated from the analog audio broadcast is also a characteristic that the audio signal is output as a monaural signal, that is, the analog channel mixer 506 has the left channel and the right channel. The case where the characteristic 1101 of the analog channel mixer 506 shown in FIG. 10b is set so that the characteristic is obtained by mixing the channels one-to-one and outputting them as the left channel and right channel audio signals. An example is shown.

  As shown in FIG. 8a, when analog audio broadcasting is an output target, the main channel ratio of the channel mixer 503 is set to 100%, and the separation characteristic of the output audio signal at this time is as shown in FIG. 8b. The separation characteristic (in this example, monaural characteristic) output from the analog channel mixer 506 remains unchanged.

  Then, when the output target is switched to the digital audio broadcasting from this state, as shown in FIG. 8a, the analog audio broadcasting is increasing at a constant rate of increase, and therefore with a constant time constant up to 100% with the main channel ratio. As long as there is no prediction of switching to, it will increase, and after that, it will be fixed at 100% until switching prediction to analog audio broadcasting occurs. The separation characteristic of the output audio signal at this time is a separation characteristic that depends only on the main channel ratio, as shown in FIG. 8b.

  Next, when a prediction to switch to analog audio broadcasting occurs after that, unless the prediction to switch to analog audio broadcasting is canceled, as shown in FIG. 8a, the main channel has a constant decrease rate and therefore a constant time constant. It decreases to 50% with a ratio. Further, the separation characteristic of the output audio signal at this time is a separation characteristic depending only on the main channel ratio, as shown in FIG. 8b.

  When switching to analog audio broadcasting occurs, the main channel ratio of the channel mixer 503 is set to 100%. The separation characteristic of the output audio signal at this time remains the separation characteristic (in this example, monaural characteristic) output from the analog channel mixer 506 as shown in FIG. 8b.

  In addition, in the above operation, when switching to the analog audio broadcasting occurs while switching to the digital audio broadcasting and the main channel ratio is increased to 100% at a constant increase rate, FIG. Thus, the main channel ratio decreases from the current channel ratio to 50% at a constant reduction rate, and the separation characteristic of the output audio signal at this time is a separation characteristic depending only on the main channel ratio as shown in FIG. It becomes. When switching to analog audio broadcasting occurs, the main channel ratio of the channel mixer 503 is set to 100% as shown in FIG. 8c. The separation characteristic of the output audio signal at this time remains the separation characteristic (in this example, monaural characteristic) output from the analog channel mixer 506 as shown in FIG. 8d.

  In addition, in the above operation, when switching prediction to analog audio broadcasting occurs and switching prediction to analog audio broadcasting is canceled while the main channel ratio is decreasing at a constant reduction rate to 50%, the main channel is canceled. The ratio increases from the current channel ratio to a constant increase rate of 100%, and the separation characteristic of the output audio signal at this time is a separation characteristic depending only on the main channel ratio, as shown in FIG. 8d.

  As described above, as can be understood from FIGS. 8B and 8D, according to the separation characteristic control process described above, the separation characteristic of the output audio signal gradually changes when switching between the analog audio broadcast and the digital audio broadcast of the output target broadcast. A sudden change in the separation characteristic of the output audio signal is suppressed. Therefore, it is possible to prevent the user from feeling uncomfortable due to a sudden change in the separation characteristic of the output sound when switching between the analog audio broadcast and the digital audio broadcast of the target broadcast.

The second embodiment of the present invention has been described above.
By the way, in the above embodiment, when the output is switched from the analog audio broadcast to the digital audio broadcast, the separation characteristic of the audio signal that is gradually output is increased over a certain time after the switch, or the digital signal in the near future is increased. When switching from an audio broadcast to an analog audio broadcast is predicted, the separation characteristic of the audio signal that is gradually output is reduced. The gradual control of the audio signal that is output in this way Similarly to the embodiment, the separation characteristic of the output audio signal may be realized as a function of the reception electric field strength SM.

  That is, now, assuming that the separation characteristic that the analog channel mixer gives to the audio signal from the analog audio broadcast according to the received electric field strength SM is as shown in FIG. 9a, for example, as shown in FIG. 9b, the received electric field strength SM Of the received electric field strength SM is less than or equal to Thb when the current level is at a level (a level exceeding Tha) that is not expected to change to a level for switching to analog audio broadcasting in the near future (a level below Thb). Thus, the main channel ratio is controlled according to the relationship with the received electric field strength SM shown in FIG. 9b until switching to analog audio broadcasting.

  That is, if the reception electric field strength SM is equal to or less than Tha and the occurrence of switching to the analog audio broadcast of the broadcast to be output in the near future is predicted, if the reception electric field strength SM exceeds Tha, the main channel ratio Is 100%. On the other hand, when the received electric field strength SM is equal to or less than Tha, the separation characteristic (monaural characteristic in the figure) given by the analog channel mixer 506 at the position where the received electric field intensity SM is Thb, and the channel mixer 503 receives the audio signal from the digital audio broadcast. The main channel ratio is reduced as the received electric field strength SM decreases so that the separation characteristics given to the same.

  As a result, as shown in FIG. 9d910, when the reception electric field strength SM is actually less than Thb and switching to the analog audio broadcast is performed, the separation characteristic reaches the separation characteristic provided by the analog channel mixer 506 for the analog audio broadcast. Since it changes gradually, even if switching to analog audio broadcasting, a steep change in separation characteristics does not occur.

  When the received electric field strength SM becomes equal to or less than Thb, switching to analog audio broadcasting is performed as shown in FIG. 9c901, the main channel ratio is set to 100%, and thereafter the received electric field strength SM reaches Thc> Thb. Up to this point, the main channel ratio is controlled according to the relationship with the reception electric field strength SM shown in FIG. 9c901. When the received electric field strength SM reaches Thc, switching to digital audio broadcasting is performed, and the separation characteristic that matches the separation characteristic given by the analog channel mixer 506 when the received electric field strength SM is Thc is switched to the digital audio broadcast. Is the ratio of the main channel given to the audio signal from the digital audio broadcast. After that, when the received electric field strength SM is between Thc and Thd> Thc, the main channel ratio increases as the received electric field strength SM increases according to the relationship with the received electric field strength SM shown in FIG. 9c902. When the received electric field strength SM is between Thc and Thb, the separation characteristic that matches the separation characteristic given by the analog channel mixer 506 at each time point is digitally converted according to the relationship with the received electric field intensity SM shown in FIG. 9c903. The main channel ratio is controlled so as to be given to the audio signal from the audio broadcast.

When the received electric field strength SM reaches Thd, the control returns to the main channel control according to the relationship of FIG. 9b. On the other hand, when the received electric field strength SM reaches Thc, the broadcast to be output is switched to the analog audio broadcast, and the control returns to the main channel control according to the relationship of FIG. 9c901.
As a result, after the reception electric field strength SM exceeds Thc and the switching to the digital audio broadcasting is performed, the separation characteristic of the output audio signal gradually increases as shown in FIG. 9d911. There is no steep change in the output audio band at the time of switching.

  Note that the reception electric field strength level Thc for switching from analog audio broadcasting to digital audio broadcasting is set to a level higher than the reception electric field strength level Thb for switching from digital audio broadcasting to analog audio broadcasting. Is set to the same level to eliminate frequent switching between digital audio broadcasting and analog audio broadcasting when the received electric field strength SM continues to fluctuate in the vicinity of the level. .

  Therefore, when other means are used to deal with such fluctuations in the received electric field strength SM in the vicinity of the level, for example, as shown in FIG. 9e, the received electric field strength SM is uniquely separated. The main channel ratio may be controlled so as to define the characteristics, and switching between digital audio broadcasting and analog audio broadcasting may always be performed with Thb as a boundary.

  In the above embodiment, the separation characteristics of the audio signal to be output are controlled using the two mixers of the analog channel mixer 506 and the channel mixer 503. However, this may be performed using only the channel mixer 503. Good. That is, in this case, when the analog audio broadcast is the output target broadcast, the separation characteristic control performed by the analog channel mixer 506 is performed instead of setting the main channel ratio to 100% in the channel mixer 503. You can do it.

It is a block diagram which shows the structure of the audio broadcasting receiver which concerns on 1st Embodiment of this invention. It is a figure which shows the frequency response characteristic of the bandpass filter and variable bandpass filter which are used in 1st Embodiment of this invention. It is a figure which shows the relationship between the high frequency side cut-off frequency and receiving electric field strength of the variable bandpass filter used in 1st Embodiment of this invention. It is a flowchart which shows the procedure of the broadcast switching process which concerns on 1st Embodiment of this invention. It is a block diagram which shows the structure of the audio broadcasting receiver which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the structure of the variable frequency filter and channel mixer which are used in 2nd Embodiment of this invention. It is a flowchart which shows the procedure of the separation characteristic control process which concerns on 1st Embodiment of this invention. It is a figure which shows the example of control of the separation characteristic which concerns on 1st Embodiment of this invention. It is a figure which shows the example of control of the other separation characteristic which concerns on 1st Embodiment of this invention. It is a figure which shows the relationship between the output audio | voice band and reception electric field strength in the conventional audio broadcasting receiver.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Operation part, 2 ... Display apparatus, 3 ... Control part, 4 ... Tuner, 5 ... Analog broadcast decoder, 6 ... Band filter, 7 ... Digital broadcast decoder, 8 ... Variable band filter, 9 ... Buffer circuit, 10 ... Digital-analog converter, 11 ... Selector, 12 ... Amplifier, 13 ... Speaker, 501 ... Frequency filter, 502 ... Variable Frequency filter, 503, channel mixer, 504, analog audio peak detector, 505, digital audio peak detector, 506, analog channel mixer.

Claims (10)

An audio broadcast receiving device,
A tuner that receives digital audio broadcasting and analog audio broadcasting in parallel;
Audio output means for outputting an audio signal received by the digital audio broadcast;
Monitoring means for monitoring the reception status of the digital audio broadcast;
When the reception state of the digital audio broadcast monitored by the monitoring means deteriorates from a switching level that is a predetermined level, the audio signal output by the audio output means is temporarily received by the digital audio broadcast. Broadcast switching means for switching from the audio signal to the audio signal received in the analog audio broadcast;
Output audio characteristic control means for controlling the acoustic characteristics of the audio signal output by the audio output means,
The output sound characteristic control means includes:
When the reception state of the digital audio broadcast monitored by the monitoring unit is maintained at a level better than the first level, which is a level at which the reception state is better than the switching level, the acoustic characteristics are: Control to a first characteristic value defined for an audio signal received in the digital audio broadcast;
When the reception state of the digital audio broadcast monitored by the monitoring unit deteriorates from a state better than the first level to a level between the first level and the switching level, the acoustic characteristics are changed. , The closer to the first level the reception state of the digital audio broadcast is, the closer to the first characteristic value, and the closer the reception state of the digital audio broadcast is to the switching level, the audio signal received by the analog audio broadcast Control to approach the second characteristic value set for
The acoustic characteristic is controlled to the second characteristic value when a reception state of the digital audio broadcast monitored by the monitoring unit deteriorates from a level better than the switching level to the switching level. An audio broadcast receiver. The audio broadcast receiving device according to claim 1,
The broadcast switching means is monitored by the monitoring means after the audio signal output from the audio output means is switched from an audio signal received by the digital audio broadcast to an audio signal received by the analog audio broadcast. The audio signal output by the audio output means when the reception state of the digital audio broadcast reaches a return level that is equal to the switching level or a predetermined level in which the reception state is better than the switching level. From the audio signal received in step 1, the audio signal received in the digital audio broadcast is restored.
The output audio characteristic control means, after the broadcast switching means returns the audio signal output by the audio output means to the audio signal received by the digital audio broadcast,
The reception state of the digital audio broadcast monitored by the monitoring means is the return level and a second level in which the reception state is better than the return level and is the same level as or different from the first level. When the digital audio broadcast reception state is closer to the return level, the acoustic characteristic approaches the second characteristic value, and the digital audio broadcast reception state is the second characteristic value. Control closer to the first characteristic value closer to the level,
The audio characteristic is controlled to the first characteristic value when the reception state of the digital audio broadcast monitored by the monitoring unit becomes better than the second level. Broadcast receiving device. The audio broadcast receiving device according to claim 2,
The audio broadcast receiving apparatus according to claim 1, wherein the return level is a level in which a reception state is better than the switching level. The audio broadcast receiving device according to claim 1, 2, or 3,
The acoustic characteristic is a characteristic of a voice band of an audio signal output from the audio output means, and a voice band based on the first characteristic value has a higher upper limit frequency than a voice band based on the second characteristic value. A featured audio broadcast receiver. The audio broadcast receiving device according to claim 1, 2, or 3,
The audio characteristic is a channel separation characteristic of an audio signal output from the audio output means, and the first characteristic value has a higher degree of channel separation than the second characteristic value. Broadcast receiving device. The audio broadcast receiver according to claim 1, 2, 3, 4 or 5,
The audio broadcast receiving apparatus characterized in that the monitoring means monitors the reception intensity of the digital audio broadcast of the tuner as a reception state of the digital audio broadcast. Digital audio broadcast and analog audio broadcast are received in parallel, and the audio signal received in the digital audio broadcast is output when the reception state of the digital audio broadcast is not deteriorated below a predetermined switching level. In the audio broadcast receiving apparatus that outputs an audio signal received by the analog audio broadcast when a reception state of the digital audio broadcast is deteriorated from the switching level, an output audio characteristic that controls an acoustic characteristic of the output audio signal A control method,
When the reception state of the digital audio broadcast is maintained at a level better than the first level, which is a level at which the reception state is better than the switching level, the acoustic characteristics are received by the digital audio broadcast. Controlling to a first characteristic value defined for the audio signal;
When the reception state of the digital audio broadcast deteriorates from a state better than the first level to a level between the first level and the switching level, the acoustic characteristics are received as the reception of the digital audio broadcast. The closer the state is to the first level, the closer to the first characteristic value, and the closer the reception state of the digital audio broadcast is to the switching level, the second predetermined for the audio signal received by the analog audio broadcast. Controlling to approach the characteristic value;
And controlling the acoustic characteristic to the second characteristic value when the reception state of the digital audio broadcast has deteriorated from a level better than the switching level to the switching level. An output sound characteristic control method in a broadcast receiving apparatus. An audio output characteristic control method for an audio broadcast receiver according to claim 7,
The reception state of the digital audio broadcast monitored by the monitoring means after the audio signal output by the audio output means is switched from the audio signal received by the digital audio broadcast to the audio signal received by the analog audio broadcast Audio signal output by the audio output means from the audio signal received by the analog audio broadcast when the return level is equal to the switching level or a predetermined level in which the reception state is better than the switching level. Returning to the audio signal received by the digital audio broadcast;
After the audio signal output from the audio output means is restored to the audio signal received by the digital audio broadcast, the reception state of the digital audio broadcast is a level that is better in the reception state than the return level and the return level. And when it is at a level between a second level that is the same as or different from the first level, the acoustic characteristics are expressed as the reception state of the digital audio broadcast is closer to the return level. 2 is controlled so as to approach the first characteristic value as the reception state of the digital audio broadcast approaches the second level, and the reception state of the digital audio broadcast is set to the second level. The acoustic characteristic is controlled to the first characteristic value. Output audio characteristic control method in the audio broadcast receiver to. An output audio characteristic control method for an audio broadcast receiver according to claim 7 or 8,
The acoustic characteristic is a characteristic of a voice band of an audio signal output from the audio output means, and a voice band based on the first characteristic value has a higher upper limit frequency than a voice band based on the second characteristic value. An output audio characteristic control method in an audio broadcast receiving apparatus. An output audio characteristic control method for an audio broadcast receiver according to claim 7 or 8,
The audio characteristic is a channel separation characteristic of an audio signal output from the audio output means, and the first characteristic value has a higher degree of channel separation than the second characteristic value. An output sound characteristic control method in a broadcast receiving apparatus.

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