JP2011109378A - Broadcast receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a broadcast receiver suitable for avoiding degradation of sound quality during analog broadcast while reducing an uncomfortable feeling or the like to a user in switching digital broadcast to the analog broadcast and vice versa. <P>SOLUTION: The broadcast receiver includes: a detection means to detect reception quality of a broadcast signal; a condition determination means to determine whether the reception quality satisfies a first or second condition; a sound quality setting change means to change the setting from initial analog sound quality characteristics related to the sound quality of the analog broadcast into intermediate sound quality characteristics between digital sound quality characteristics related to the sound quality of digital broadcast and the initial analog sound quality characteristics when at least the first condition is satisfied; and a reproduction changeover means to reproduce the digital broadcast if the second condition is satisfied and the analog sound quality characteristics are set at the intermediate sound quality characteristic, otherwise to reproduce the analog broadcast. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a broadcast receiver, and more particularly, to a broadcast receiver suitable for receiving a broadcast signal transmitted by a signal format of a system for simultaneously broadcasting a digital broadcast and an analog broadcast.

  In recent years, it has become common to process and manage audio and video in digital format in audio equipment and video equipment. The trend of digital encoding of audio and video in such audio equipment has spread to the field of radio broadcasting, and several types of digital radio broadcasting have been standardized and put into practical use. For example, in the United States, a digital radio broadcasting system using OFDM (Orthogonal Frequency Division Multiplex) called IBOC (In-Band On-Channel) has been proposed and put into practical use by iBiquity.

  Here, a conventional analog radio broadcast is broadcast using a carrier wave having a frequency distribution in a frequency band assigned to each broadcast station (hereinafter referred to as “analog carrier wave”). However, analog carriers are not transmitted using all the assigned frequency bands. Specifically, in order to avoid interference between analog carriers in adjacent channels (that is, frequency bands assigned to different broadcasting stations), only the central part of the assigned frequency bands is used for analog carrier transmission. Other parts are not used. That is, in analog radio broadcasting, a frequency band adjacent to an analog carrier (hereinafter referred to as “sideband”) is not effectively utilized.

  The IBOC signal transmission format includes a hybrid format that transmits a digital radio broadcast signal together with an analog carrier wave using a sideband that has not been effectively used in the past, or a digital radio broadcast signal that is transmitted using a sideband. The all-digital format is specified, and it is designed so that the existing analog radio broadcast can be gradually shifted to a multi-function, high-quality all-digital format broadcast. In the transition period from analog radio broadcasting to all-digital broadcasting, signal transmission in a hybrid format is mainly used, and analog radio broadcast signals and digital radio broadcast signals are transmitted by the simulcast method using the same frequency band. The

  IBOC digital radio broadcasting performs signal transmission by OFDM modulation, and therefore has higher frequency utilization efficiency and resistance to multipath fading than analog radio broadcasting. That is, digital radio broadcasting has higher sound quality than analog radio broadcasting because of its large transmission capacity and high noise resistance. Accordingly, an HD (High Definition) radio that receives an IBOC radio broadcast reproduces the digital radio broadcast if the quality of the received signal is equal to or higher than a predetermined level when the hybrid format broadcast is received. If the signal cannot be decoded, the output is switched to reproduce the analog radio broadcast. As a result, a high-quality digital radio broadcast is provided to the user, and the problem that the silent state continues at the time of a decoding error is effectively avoided. The quality of the received radio wave is likely to deteriorate in a weak electric field area far from the broadcast base station or in a place where the influence of multipath fading is strong such as an urban area.

  By the way, when reproduction by HD radio is switched between digital radio broadcasting and analog radio broadcasting, it has been regarded as a problem that the sound volume changes suddenly to give the user a sense of discomfort and discomfort. Thus, for example, Patent Literature 1 proposes a broadcast receiver that performs volume matching at the time of switching in order to reduce discomfort and discomfort due to sudden changes in volume.

JP 2000-110502 A

  However, it is pointed out that the uncomfortable feeling and the uncomfortable feeling cannot be sufficiently reduced only by the volume matching. For example, in a general reproduction process of analog radio broadcasting, as a measure for suppressing an increase in noise when the quality of received radio waves deteriorates, the sense of stereo is eliminated or the gain (particularly, the high frequency is reduced) is adjusted. In this case, since there is a large difference in sound quality when switching from analog radio broadcasting to digital radio broadcasting, a sense of discomfort and discomfort given to the user is further increased. Therefore, in order to reduce discomfort and discomfort due to the difference in sound quality at the time of switching, it is conceivable to set the sound quality characteristics at the time of analog radio broadcasting to characteristics close to the sound quality characteristics at the time of digital radio broadcasting. However, in this case, during analog radio broadcasting, there is a concern that noise is conspicuous due to inconsistency in the sound quality characteristics, which may lower the sound quality.

  Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to reduce the sound quality during analog broadcasting while reducing discomfort to the user when switching between digital broadcasting and analog broadcasting. It is an object to provide a broadcast receiver suitable for avoiding the above.

  A broadcast receiver according to an embodiment of the present invention that solves the above problem is an apparatus suitable for receiving a broadcast signal transmitted in a signal format of a system that simultaneously broadcasts a digital broadcast and an analog broadcast. Detection means for detecting the reception quality of the signal; condition determination means for determining whether the detected reception quality satisfies the first condition or a second condition better than the first condition; and at least a first When the above condition is satisfied, the initial analog sound quality characteristic related to the sound quality of analog broadcasting is changed to a sound quality characteristic intermediate between the digital sound quality characteristic related to the sound quality of digital broadcasting and the initial analog sound quality characteristic. When the setting change means and the second condition are satisfied and the analog sound quality characteristic is set to an intermediate sound quality characteristic, the digital broadcast is played, otherwise, And having a playback switching means for reproducing analog broadcasting.

  According to the broadcast receiver according to the present invention, since the difference in sound quality when switching from analog broadcasting to digital broadcasting is reduced, the user's discomfort and discomfort are reduced, and the initial condition is satisfied unless the first condition is satisfied. Since analog broadcasting is reproduced with sound quality characteristics, an increase in noise due to mismatch of sound quality characteristics can be effectively avoided.

  The broadcast receiver according to the present invention switches from reproduction of digital broadcast to reproduction of analog broadcast based on the initial analog sound quality characteristics in order to further enhance the effectiveness of mitigation of a sense of incongruity when switching between analog broadcast and digital broadcast. In the process, or in the process of switching from the reproduction of the analog broadcast based on the initial analog sound quality characteristic to the reproduction of the digital broadcast, the reproduction of the analog broadcast based on the intermediate sound quality characteristic may be maintained for at least a fixed time.

  Here, the sound quality characteristics relating to digital broadcasting or analog broadcasting include, for example, at least frequency characteristics or separation characteristics.

  The first or second condition is determined using, for example, at least one of BER (Bit Error Rate), S meter value, CN ratio, and SN ratio measured based on a broadcast signal.

  The broadcast receiver according to the present invention may have a configuration suitable for receiving a broadcast signal transmitted in an IBOC signal format.

  The broadcast receiver according to the present invention may be a device mounted on a moving body such as a general passenger car.

  ADVANTAGE OF THE INVENTION According to this invention, the broadcast receiver suitable for avoiding deterioration of the sound quality at the time of analog broadcasting, reducing the discomfort etc. with respect to a user at the time of the switching between digital broadcasting and analog broadcasting is provided.

It is a block diagram which shows the structure of HD radio of embodiment of this invention. It is a flowchart which shows the reproduction signal switching process performed in embodiment of this invention. It is a figure which shows the frequency characteristic or separation characteristic of the broadcast signal of each format in IBOC. It is a figure which shows the frequency characteristic or separation characteristic of the broadcast signal of each format in IBOC.

  Hereinafter, a broadcast receiver according to an embodiment of the present invention will be described with reference to the drawings. The broadcast receiver of this embodiment is an HD radio suitable for receiving IBOC radio broadcasts.

  FIG. 1 is a block diagram showing a configuration of an HD radio 100 according to an embodiment of the present invention. The HD radio 100 is a vehicle-mounted broadcast receiver and is installed in a general passenger car or the like. The HD radio 100 is designed to be compatible with IBOC radio broadcasting, and is configured to receive and process broadcast signals in the signal format of the system.

  The HD radio 100 includes an antenna 1, a tuner 2, an IF (Intermediate Frequency) filter 5, an IF amplifier 6, a separator SEP, an IF filter 7, an A / D converter 8, an analog signal processing circuit 9, an audio signal processing unit 10, D / A converter 11, power amplifier 12, speaker 13, PLL (Phase Locked Loop) circuit 14, microcomputer 15, IDM (IBOC Digital Module) 16, light receiving unit 17, remote controller (hereinafter referred to as “remote controller”) 18 A display control circuit 19, a display 20, and a flash memory 21.

  The remote controller 18 is provided with operation keys for operating the HD radio 100. The remote controller 18 outputs a control pulse corresponding to the user's key operation. This control pulse is, for example, a signal conforming to the IrDA standard. The light receiving unit 17 outputs the received control pulse to the microcomputer 15.

  Various control programs for executing various functions of the HD radio 100 are installed in the microcomputer 15. The microcomputer 15 performs hardware management of the HD radio 100, execution of various functions based on control pulses from the light receiving unit 17, and the like.

  The HD radio 100 processes and reproduces the radio broadcast signal as follows. That is, the HD radio 100 receives broadcast radio waves by the antenna 1 and outputs them to the tuner 2. The tuner 2 extracts an RF (Radio Frequency) signal of the selected channel from the received radio wave under the control of the microcomputer 15 via the PLL circuit 14. The extracted RF signal is frequency-converted to an intermediate frequency suitable for signal processing such as filtering. The tuner 2 outputs an IF signal obtained by frequency conversion to the IF filter 5.

  The channel selection channel is determined according to a channel selection operation by the user using the remote controller 18 or the like. Information on the channel selected last (hereinafter referred to as “last channel”) is held in the flash memory 21. For example, immediately after the HD radio 100 is turned on, the flash memory 21 is read and the last channel is selected.

  The IF signal output from the tuner 2 is input to the IF amplifier 6 after being filtered by the IF filter 5. The IF amplifier 6 amplifies the input IF signal and outputs the amplified IF signal to the separator SEP. The amplification factor of the IF amplifier 6 is adjusted by feedback control so that the output signal from the IF amplifier 6 has a set intensity regardless of the intensity of the input signal to the IF amplifier 6.

  The separator SEP separates the input IF signal into two signal components. One of the separation components is a signal component obtained by converting an analog carrier wave into an IF signal, and the other is a signal component obtained by converting a sideband subcarrier into an IF signal. In the following, for convenience of explanation, the former signal component is referred to as an “analog IF signal”, and the latter signal component is referred to as a “digital IF signal”. The separator SEP outputs an analog IF signal to the IF filter 7 and outputs a digital IF signal to the A / D converter 8.

  The above description is based on the premise that the channel selection channel is a channel in a hybrid format. Of course, when only the analog radio broadcast (or digital radio broadcast) is broadcast on the selected channel, the digital IF signal (or analog IF signal) separated by the separator SEP does not contain an effective signal component.

  The IF filter 7 filters the input analog IF signal to remove unnecessary frequency components. The IF filter 7 outputs the filtered analog IF signal to the A / D converter 8.

  The A / D converter 8 includes A / D conversion processing circuits separately for an analog IF signal and a digital IF signal. The A / D converter 8 performs A / D conversion on each input IF signal by a corresponding processing circuit. The A / D converted analog IF signal is output to the analog signal processing circuit 9, and the digital IF signal is output to the IDM 16, respectively.

  The analog signal processing circuit 9 includes a detection circuit 9a, a noise canceller 9b, and a weak electric field processing circuit 9c. The analog IF signal is demodulated into an audio signal by the detection circuit 9a, and then noise is removed by the noise canceller 9b. The analog IF signal is then processed by the weak electric field processing circuit 9c according to the reception state of the selected channel such as mute, high cut, and separation control. Then, it is output to the audio signal processing unit 10 as an analog audio signal.

  The analog signal processing circuit 9 has a built-in S meter 9d. The S meter 9d measures the value of the detection voltage at the time of demodulating the analog audio signal (hereinafter referred to as “S meter value”) at a predetermined sampling period and outputs it to the microcomputer 15. The S meter value is a DC voltage proportional to the received radio wave, and is correlated with the CN ratio of the received radio wave. Therefore, the microcomputer 15 can estimate the CN ratio of the received radio wave by monitoring the S meter value.

  The IDM 16 is a module designed exclusively for IBOC digital radio broadcast signal processing. The IDM 16 orthogonally demodulates the digital IF signal from the A / D converter 8 to establish reception synchronization corresponding to the guard interval length or the like by synchronous reproduction, and converts it into a bit stream. The bit stream to be converted here is a bit stream that is compression-encoded in, for example, a PAC (Perceptual Audio Corder) format. The IDM 16 can establish reception synchronization only when the IF signal includes a digital radio broadcast signal. The IDM 16 generates status information (for example, information indicating whether reception synchronization has been established) based on the demodulation processing result and outputs the status information to the microcomputer 15 every time a channel selection channel is set or changed, for example.

  The IDM 16 further decodes an error correction code included in the bit stream and performs error correction processing on the bit stream. Next, the error-corrected bit stream is separated into an audio stream and a data stream. The IDM 16 decodes the separated audio stream at a timing according to the time stamp of each packet to reconstruct a digital radio broadcast audio signal (hereinafter referred to as “digital audio signal”), and outputs it to the audio signal processing unit 10. To do. The IDM 16 also decodes the separated data stream at the same time as the decoding process for the audio stream, converts the data stream into predetermined incidental data, and transfers the data to the microcomputer 15. The incidental data is data described using an ID3 tag, and includes information on the radio broadcast being selected, such as the name of a provider that provides a broadcast service, the name of a song being broadcast, and the name of an artist.

  The IDM 16 measures the quality of the received signal based on the CN ratio and SN ratio of the signal obtained by the demodulation process, the BER calculated by the error correction process, and the like, and generates a blend signal based on the measurement result. The generated blend signal is output to the audio signal processing unit 10.

  The audio signal processing unit 10 includes a blend circuit 10a and an audio processing circuit 10b. The blend circuit 10a performs a blend process on the analog audio signal from the analog signal processing circuit 9 and the digital audio signal from the IDM 16 based on the input blend signal.

  Here, in the broadcast of the hybrid format, the digital radio broadcast has a higher quality than the analog radio broadcast. Therefore, when the quality level of the received signal is equal to or higher than the predetermined level, the blend circuit 10a attenuates the analog audio signal based on the blend signal so that substantially only the digital audio signal is output. If the quality level of the received signal is less than the predetermined level, or if the user is set to play only analog radio broadcasts, only the analog audio signal will be output based on the blend signal. So that the digital audio signal is attenuated. Further, when the quality level of the received signal changes over a predetermined level, the blend circuit 10a performs correction in consideration of the delay amount, quality difference, etc. between the analog audio signal and the digital audio signal based on the blend signal. While mixing the signals, the audio signals to be output are switched so that the voices before and after the switching are smoothly connected. The time required for switching at this time is, for example, about 900 ms. The audio signal output from the blend circuit 10a is input to the audio processing circuit 10b, and is output to the D / A converter 11 after predetermined signal processing by the audio processing circuit 10b.

  The audio signal input to the D / A converter 11 is input to the power amplifier 12 after D / A conversion. The audio signal input to the power amplifier 12 is gain-adjusted with an amplification factor corresponding to the volume and output to the speaker 13. Through the above signal processing, the radio broadcast of the selected channel is reproduced by the speaker 13.

  The microcomputer 15 interprets the accompanying data (data described by the ID3 tag) from the IDM 16 and outputs the interpretation result to the display control circuit 19. The display control circuit 19 performs a predetermined process on the input interpretation result and outputs the result to the display 20. Thereby, information corresponding to the accompanying data is displayed on the display 20.

  By the way, in the IBOC system, since the baseband signal is primarily modulated by QPSK (Quadrature Phase Shift Keying) having a long symbol length, signal transmission that is strong against multipath fading and suitable for reception by a mobile unit is realized. . However, in places where the effects of multipath fading are extremely strong, such as in high-rise buildings, the broadcast radio waves are unstable, so the quality of the received radio waves varies, and playback by the HD radio 100 is digital radio broadcast and analog radio broadcast. Switch between and. For this reason, the above-described problem caused by the sound quality difference between the audio signals of the respective formats of the digital audio signal and the analog audio signal occurs. In order to solve this problem, the HD radio 100 of the present embodiment executes a playback broadcast switching process described below.

  FIG. 2 is a flowchart of playback broadcast switching processing executed in the present embodiment. This playback / broadcast switching processing is started when the HD radio 100 is activated and is terminated when the system is stopped. In the present embodiment, for convenience of explanation, it is assumed that only the analog radio broadcast can be received when the execution of the playback broadcast switching process is started. In the following description and drawings in this specification, each step of the playback / broadcast switching process is abbreviated as “S”.

  FIG. 3A and FIG. 4A show the frequency characteristics of broadcast signals of various formats in IBOC. 3A and 4A, the vertical axis represents gain (unit: dB), and the horizontal axis represents frequency (unit: Hz). The frequency characteristics shown here indicate the relationship between the frequency on the receiving side and the volume level when the source sound on the transmitting side has a certain level of volume at all frequencies. FIGS. 3B and 4B show the separation characteristics of broadcast signals of various formats in the IBOC. 3B and 4B, the vertical axis indicates the degree of separation (unit: dB), and the horizontal axis indicates the frequency (unit: Hz). The separation characteristics shown here indicate the ratio between the signal leaking from other channels and the self channel level. In each figure, the solid line indicates the characteristics of digital radio broadcasting, the alternate long and short dash line indicates the characteristics of analog FM radio broadcasting, and the dotted line indicates the characteristics of analog AM radio broadcasting.

  FIGS. 3A and 3B show general frequency characteristics and separation characteristics of digital radio broadcast and analog radio broadcast, respectively. As shown in FIG. 3 (a), the frequency characteristics of digital radio broadcasting are good over almost the entire range of audible frequencies. On the other hand, degradation is significant in analog FM radio broadcasting in a high frequency band, and in analog AM radio broadcasting in a low frequency band and a high frequency band. Further, as shown in FIG. 3B, the separation characteristic of analog FM radio broadcasting is deteriorated as compared with the separation characteristic of digital radio broadcasting. Differences in characteristics between digital radio broadcasting and analog radio broadcasting shown in each figure appear as sound quality differences during playback. Note that the frequency characteristic of the analog FM radio broadcast shown in FIG. 3A is, for example, −3 dB at 7 KHz, and is hereinafter referred to as “F1”. Further, the separation characteristic of the analog FM radio broadcast shown in FIG. 3B is, for example, 20 dB, and is hereinafter referred to as “Sep1”. In the following, for the sake of avoiding duplication of explanation, the reproduction broadcast switching process between the digital radio broadcast and the analog FM radio broadcast will be described, and the description of the reproduction broadcast switching process between the digital radio broadcast and the analog AM radio broadcast will be omitted.

  The values of the frequency characteristic F1 and the separation characteristic Sep1 are stored in advance in a storage medium such as an internal memory (not shown) of the microcomputer 15 or the flash memory 21. In the process of S1, this storage medium is accessed and the frequency characteristics and separation characteristics of analog FM radio broadcasting are set to F1 and Sep1, respectively.

  When a digital radio broadcast is broadcast on the selected channel, synchronization is established by the IDM 16, error correction processing, and the like are performed. In the process of S2, it is determined whether or not the BER calculated in the error correction process is equal to or less than a threshold value B (unit:%). This threshold value B is defined as a value that satisfies A <B when the BER required for normal decoding of digital radio broadcasting is equal to or less than the threshold value A (unit:%, eg, 0.0005%). The Here, the threshold value B is set to 0.005%, for example.

  When the BER is equal to or lower than the threshold B (S2: YES), the quality of the received signal is relatively good, and at least analog radio broadcast is reproduced with high sound quality (in other words, sound quality relatively close to digital radio broadcast). be able to. In this case, the reproduction / broadcast switching process proceeds to the process of S3. If the BER exceeds the threshold B (S2: NO), the process returns to S1.

  In the storage medium, values of the frequency characteristic F2 of the analog FM radio broadcast shown in FIG. 4A and the separation characteristic Sep2 of the analog FM radio broadcast shown in FIG. 4B are stored in advance. The frequency characteristic F2 is defined as a value positioned between the frequency characteristic F1 and the frequency characteristic of digital radio broadcasting, and the separation characteristic Sep2 is defined as a value positioned between the separation characteristic Sep1 and the separation characteristic of digital radio broadcasting. Is done. That is, the frequency characteristic F2 and the separation characteristic Sep2 are values closer to the frequency characteristic and the separation characteristic of digital radio broadcasting than the frequency characteristic F1 and the separation characteristic Sep1, respectively. For example, the frequency characteristic F2 is -1 dB at 7 KHz, and the separation characteristic Sep2 is 30 dB.

  In the process of S3, the storage medium is accessed and the frequency characteristics and separation characteristics of the analog FM radio broadcast are set to F2 and Sep2, respectively, to approach the frequency characteristics and separation characteristics of the digital radio broadcast. Therefore, the analog FM radio broadcast is reproduced with a sound quality close to that of the digital radio broadcast.

  In the process of S4, it is determined whether or not the BER is equal to or less than the threshold A. If the BER is less than or equal to the threshold A (S4: YES), the process proceeds to S5. If the BER exceeds the threshold A (S4: NO), the process returns to S2.

  In the process of S5, since the digital radio broadcast is normally decoded, the blend circuit 10a is controlled to switch the output audio signal from the analog audio signal to the digital audio signal. Digital radio broadcasts are reproduced with sound quality having good characteristics shown in FIG. 3 or FIG.

  According to the above description, analog FM radio broadcasting is stepped to sound quality approximating to digital radio broadcasting by resetting each characteristic related to sound quality such as frequency characteristics and separation characteristics before switching to digital radio broadcasting. It has been changed to be played. Therefore, the difference in sound quality when switching from analog FM radio broadcasting to digital radio broadcasting is reduced, and the user feels uncomfortable and uncomfortable. Further, the sound quality change of the analog FM radio broadcast is surely executed before switching to the digital radio broadcast by setting a threshold value B higher than the threshold value A. Further, the characteristics of analog FM radio broadcasting related to sound quality are basically set to a general frequency characteristic F1 and a separation characteristic Sep1. Therefore, at the time of reproduction of analog FM radio broadcast, increase of noise due to mismatch of these characteristics can be effectively avoided.

  In the process of S6, quality degradation of the received signal is detected. The process of S6 is continuously executed until, for example, a BER exceeding the threshold A is detected. If a BER exceeding the threshold A is detected, the process proceeds to S7.

  In the process of S7, the storage medium is accessed and the frequency characteristics and separation characteristics of the analog FM radio broadcast are set to F2 and Sep2, respectively. After each characteristic setting, the process returns to S2. Thereafter, when the BER becomes equal to or lower than the threshold value A, the digital radio broadcast is switched again. If the BER exceeds the threshold value B, the frequency characteristics and separation characteristics of the analog FM radio broadcast are set to F1 and Sep1, and the analog FM radio broadcast is reproduced with a general sound quality. That is, even when the digital radio broadcast is switched to the analog FM radio broadcast, the characteristics related to the sound quality can be changed step by step. Therefore, the difference in sound quality when switching from digital radio broadcasting to analog FM radio broadcasting is reduced, and the user feels uncomfortable and uncomfortable.

The above is the description of the embodiment of the present invention. The present invention is not limited to the above-described configuration, and various modifications can be made within the scope of the technical idea of the present invention. For example, a broadcast receiver according to the present invention includes XM Satellite Radio, Sirius Satellite Radio, DAB (Digital Audio
It is good also as an apparatus suitable for reception of other digital broadcasting systems, such as Broadcasting), DMB (Digital Multimedia Broadcasting), ISDB-T (Integrated Services Digital Broadcasting-Terrestrial).

  The threshold used for executing the determination process of S2 or S4 in FIG. 2 is not limited to BER. Instead of BER or selectively, for example, an S meter value, a CN ratio, an SN ratio, or the like may be used as a threshold value. For example, in a reception environment where BER cannot be obtained, a form in which the S meter value is used as a threshold value may be considered. In the determination process of S2 or S4, whether or not the determination is possible is not limited to one threshold value, and a plurality of threshold values (for example, BER and S meter value) may be used.

  In order to further improve the effectiveness of mitigation of discomfort during switching by setting the frequency characteristics and separation characteristics in stages, when each characteristic is changed, the broadcast of the settings is not affected regardless of the quality of the received signal. Regeneration should be maintained for at least a certain time. As an example, even when a BER exceeding the threshold B is detected during playback of a digital radio broadcast, after switching to the analog FM radio broadcast, playback of the analog FM radio broadcast by setting the frequency characteristic F2 and the separation characteristic Sep2 is performed. Processing such as maintaining for a certain period of time is assumed. Since the setting change to the frequency characteristic F1 and the separation characteristic Sep1 is performed after the predetermined time has elapsed, a sudden change in sound quality is suppressed. Even if the BER suddenly changes from a value exceeding the threshold value B to a value equal to or less than the threshold value A at the time of reproduction of the analog FM radio broadcast, the frequency characteristic F2 and the separation characteristic are not intentionally switched to the digital radio broadcast. A process of maintaining the reproduction of the analog FM radio broadcast by the setting of Sep2 for a predetermined time is assumed. Since switching to digital radio broadcasting is performed after the predetermined time has elapsed, sudden changes in sound quality are suppressed.

  Further, for example, when the BER continuously exceeds the threshold value B for a certain time during reproduction of the analog FM radio broadcast, the frequency characteristics and separation characteristics of the analog FM radio broadcast are changed from F1, Sep1 to F0, Sep0, respectively. When switching from analog FM radio broadcasting to digital radio broadcasting, change the setting from F0, Sep0 to F1, Sep1 over a certain period of time, and after changing the setting to F2, Sep2, switch to digital radio broadcasting Do. Since the reproduction broadcast switching process is executed in stages and over time, sudden changes in sound quality are further suppressed.

  In order to prevent hunting in which the reproduction broadcast is switched in the vicinity of the threshold A, each threshold used in the processes of S4 and S6 in FIG. 2 may be set to a different value. Specifically, in order to effectively prevent hunting, the threshold used in the process of S4 (that is, when switching from analog FM radio broadcast to digital radio broadcast) is defined as A1, and the process of S6 (that is, digital radio broadcast) When the threshold value used in (when switching from analog FM radio broadcasting to analog FM radio) is defined as A2, for example, each threshold value may be set to satisfy A1 <A2. Needless to say, the thresholds A1 and A2 are values corresponding to the BER sufficient to normally decode the digital radio broadcast.

DESCRIPTION OF SYMBOLS 1 Antenna 2 Tuner 5, 7 IF filter 6 IF amplifier 8 A / D converter 9 Analog signal processing circuit 10 Audio signal processing part 11 D / A converter 12 Power amplifier 13 Speaker 14 PLL circuit 15 Microcomputer 16 IDM
17 Photosensitive unit 18 Remote control 19 Display control circuit 20 Display 100 HD radio SEP Separator

Claims (6)

In a broadcast receiver suitable for receiving a broadcast signal transmitted by a signal format of a method for simultaneously broadcasting a digital broadcast and an analog broadcast,
Detecting means for detecting the reception quality of the broadcast signal;
Condition determining means for determining whether the detected reception quality satisfies a first condition or a second condition better than the first condition;
When at least the first condition is satisfied, an initial analog sound quality characteristic related to the sound quality of the analog broadcast is set to an intermediate sound quality between the digital sound quality characteristic related to the sound quality of the digital broadcast and the initial analog sound quality characteristic. Sound quality setting changing means for changing the setting to the characteristics;
Playback switching means for playing back the digital broadcast when the analog sound quality characteristic is set to the intermediate sound quality characteristic while satisfying the second condition, and playing back the analog broadcast otherwise. When,
A broadcast receiver comprising:   In the process of switching from playback of the digital broadcast to playback of the analog broadcast by the initial analog sound quality characteristic, or in the process of switching from playback of the analog broadcast by the initial analog sound quality characteristic to playback of the digital broadcast, The broadcast receiver according to claim 1, wherein the reproduction of the analog broadcast by the intermediate sound quality characteristic is maintained for at least a predetermined time.   The broadcast receiver according to claim 1, wherein the sound quality characteristic relating to the digital broadcast or the analog broadcast includes at least a frequency characteristic or a separation characteristic.   The first or second condition is determined using at least one of BER (Bit Error Rate), S meter value, CN ratio, and SN ratio measured based on the broadcast signal. The broadcast receiver according to any one of claims 1 to 3.   The broadcast receiver according to any one of claims 1 to 4, wherein the broadcast receiver is suitable for receiving a broadcast signal transmitted in a signal format of an IBOC (In Band On Channel) method.   The broadcast receiver according to any one of claims 1 to 5, wherein the broadcast receiver is mounted on a mobile body.

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