JP4264047B2 - Radio broadcast receiver and control method thereof - Google Patents

Description

  The present invention relates to a radio broadcast receiver for receiving simulcast such as IBOC (In-Band-On-Channel) and a control method thereof, and more particularly, to improve switching between digital radio broadcast and analog radio broadcast during simulcast. The present invention relates to a radio broadcast receiver and method.

Patent Documents 1 and 2, in a radio broadcast receiver, the power output audio, when switching between DAB in simulcast embodiment (digital radio broadcasting) -RDS (analog radio broadcast), based on the FM modulation index of the RDS DAB And / or adjusting the volume related to the RDS to perform matching of the volume related to the DAB and the RDS, thereby disclosing the sudden change in the volume at the time of switching that is annoying to the user.

  Patent Document 3 sets a predetermined switching period, not instantaneous, for switching DAB-RDS during simulcasting, and fades out audio related to radio broadcasting before switching in the switching period, and after switching Disclosed is a volume control method for fading in audio related to radio broadcasting.

  In Patent Document 4, in order to cope with a sudden change in volume at the time of DAB-RDS switching during simulcasting, the audio volume related to the radio broadcast after switching is temporarily set to 0 without immediately changing the volume at the position of the volume operation member. Then, it is disclosed that the volume is gradually increased from 0 to the volume at the position of the volume operation member.

Patent Document 5 discloses IBOC that multiplexes digital radio broadcast and analog radio broadcast into one transmission wave.
JP2000-11002 (FIG. 6) JP 2002-9647 (paragraph 0025) JP 2000-138611 (FIG. 4) JP 2000-261338 (FIG. 2) JP2001-320290A (FIG. 3)

  Regarding the audio switching between the digital radio broadcast and the analog radio broadcast during the simulcast, the improvement in the conventional radio broadcast receiver is related to the volume matching.

  An object of the present invention is to provide a radio broadcast receiver and a control method thereof that deal with audio changes that cause discomfort to the user at the time of audio switching between digital radio broadcast and analog radio broadcast during simulcast based on a viewpoint other than volume. Is to provide.

  According to the present invention, attention is paid to the difference (see FIG. 3) in the audio frequency characteristics of the digital radio broadcast receiver and the analog radio broadcast receiver. That is, the difference in the audio frequency characteristics between the two appears as a difference in sound quality when the audio is switched between the digital radio broadcast and the analog radio broadcast, which makes the user uncomfortable. According to the present invention, the audio frequency characteristic related to the digital radio broadcast is matched with the audio frequency characteristic related to the analog radio broadcast by using the audio equalizer before the audio switching between the digital radio broadcast and the analog radio broadcast at the latest. Keep it. Thereby, at the time of switching, audio switching is performed between the digital radio broadcast and the analog radio broadcast in which the audio frequency characteristics are matched. The matching of the audio frequency characteristics means that the audio frequency characteristics are matched or equalized.

  According to the present invention, the difference in audio frequency characteristics between digital radio broadcast and analog radio broadcast at the time of audio switching between digital radio broadcast and analog radio broadcast during simulcast is eliminated, and audio output from a speaker or the like is The change in sound quality at the time of switching is removed or alleviated, so that user discomfort can be eliminated.

  1 and 2 show power spectra in FM-IBOC and AM-IBOC radio broadcasting, respectively. The center frequency of the radio broadcast transmission band is set to zero.

  The bandwidth of the transmission signal in the FM-IBOC system (FIG. 1) is in the range of ± 200 kHz. Only the analog modulation signal exists in the center frequency band, and the power of the analog modulation signal is maximum at the center frequency and decreases as the distance from the center frequency increases to both sides. The digital modulation signal exists on both sides of the frequency band of the analog modulation signal, and its power spectrum is flat within the existence band. The maximum power value of the analog modulation signal is 25 dBc / MHz higher than the power value of the digital modulation signal.

  The bandwidth of the transmission signal in the AM-IBOC system (FIG. 2) is in the range of ± 15 kHz. The analog modulation signal exists only in the central frequency band, and the power spectrum of the analog modulation signal is maximum at the center frequency, and decreases as the distance from the center frequency increases. The digital modulation signal exists over the entire bandwidth of the transmission signal, and has a step-like characteristic that is small in the frequency band overlapping with the analog modulation signal, medium in the frequency band on both sides, and large in the outer frequency band. It has become.

  FIG. 3 shows a comparison of audio frequency characteristics of each broadcasting format in IBOC. The audio frequency characteristic is a frequency-volume level relationship on the reception side when the source sound on the transmission side has a predetermined volume level regardless of the frequency. The audio frequency characteristics are different in each broadcasting format, and the response is flat over the whole range of audible frequencies in digital radio broadcasting (digital), and is good, but in FM analog radio broadcasting (analog FM) Deterioration is remarkable in the low frequency range, and in AM analog radio broadcasting (analog AM), considerable deterioration is seen in both the low frequency range and the high frequency range. In this way, as a result of the difference in audio frequency characteristics between digital radio broadcast and analog radio broadcast, when digital audio broadcast between analog radio broadcast and digital radio broadcast under simulcast implementation is switched between digital radio broadcast and analog radio broadcast. Even if the volumes related to the digital radio broadcast and the analog radio broadcast are matched, the user is given an uncomfortable feeling based on the difference in sound quality at the time of switching. In the present invention, the audio equalizer 12 (FIG. 4) is used to match the audio frequency characteristic of the analog radio broadcast with the audio frequency characteristic of the FM or AM, so that when the audio is switched between the digital radio broadcast and the analog radio broadcast. This eliminates sudden changes in sound quality and suppresses user discomfort.

  FIG. 4 is a configuration diagram of the radio broadcast receiver 10. Radio broadcast receiver 10 switches output audio to digital radio broadcast and analog radio broadcast audio in accordance with the quality of the received radio waves of digital radio broadcast, for digital radio broadcast and analog radio broadcast that are being conducted simultaneously. As a basic configuration, it has a quality detection means 11, an audio equalizer 12, an audio signal selection means 13, an audio output means 14 and an input signal change means 15, and an operation member 21 for user selection and an element that can be added as appropriate. Variable amplification means 22 is provided.

  A basic configuration of the radio broadcast receiver 10 will be described. The quality detection means 11 detects the quality of the received radio wave of the digital radio broadcast as the digital radio broadcast radio wave quality. Here, an audio signal obtained by demodulating and decoding an RF signal related to digital radio broadcast is called an original audio signal Id of digital radio broadcast, and the audio frequency characteristic of digital radio broadcast is changed to the audio frequency characteristic of analog radio broadcast. A signal whose signal level is adjusted for each of a plurality of frequency band sections of the original audio signal Id of the digital radio broadcast so as to be matched will be referred to as an adjusted audio signal Iu of the digital radio broadcast. The audio equalizer 12 generates an adjusted audio signal Iu for digital radio broadcasting. The audio signal selection means 13 uses the original audio signal Id of the digital radio broadcast as the first input signal, and the demodulated audio signal Ia of the analog radio broadcast as an audio signal obtained by demodulating the RF signal related to the analog radio broadcast. Is the second input signal, when the digital radio broadcast radio wave quality is equal to or higher than a predetermined level, the first input signal is obtained. When the digital radio broadcast radio wave quality is lower than the predetermined level, the second input signal is obtained. The selected audio signal is output as an output signal, and the selected audio signal is switched between the first and second input signals. The audio output means 14 outputs audio related to the selected audio signal. The input signal changing unit 15 changes the first input signal from the original audio signal of the digital radio broadcast to the audio signal related to the adjusted audio signal Iu of the digital radio broadcast before the switching of the selected audio signal by the audio signal selection unit at the latest. change.

  The radio broadcast receiver 10 and the radio broadcast receiver control method 50 (FIG. 5), which will be described later, differ only in category and have almost the same technical contents. Therefore, the radio broadcast receiver 10 will be described in detail.

  The radio broadcast receiver 10 is an IBOC radio broadcast receiver, for example, and is mounted on, for example, an automobile. In IBOC, digital radio broadcast and analog radio broadcast are multiplexed and transmitted by the same carrier wave. The received radio wave quality of the digital radio broadcast is determined by the electric field strength of the received radio wave, the level of the audio signal related to the analog radio broadcast, or the C / N or S / N of the signal obtained by demodulating the digital radio broadcast part of the received radio wave. Further, it can be detected from the bit error rate of the signal obtained by decoding the demodulated signal. The audio output means is, for example, a speaker or a headphone. In simulcast, digital radio broadcast audio is higher in quality than analog radio broadcast audio, so output from the audio output means is not affected as long as there is no problem with audio output from the digital radio broadcast. For example, audio related to digital radio broadcasting is selected. Audio related to digital radio broadcasting deteriorates at a stretch when the received radio wave weakens, whereas audio related to analog radio broadcasts has low quality even after the output of audio related to digital radio broadcasts has been hindered. Since the audio output is secured, it can be used as an alternative to the audio related to the digital radio broadcast when the output of the audio related to the digital radio broadcast occurs.

  The “audio signal related to the adjusted audio signal Iu of the digital radio broadcast” in the input signal changing means 15 may be the adjusted audio signal Iu itself of the digital radio broadcast, or an amplified adjusted audio signal Iv described later. Good.

  “Until switching of the selected audio signal in the audio signal selection unit at the latest” in the input signal changing unit 15 means that (a) when switching is necessary, the first input signal is changed to digital radio broadcast prior to switching. In addition to changing from the original audio signal to the audio signal related to the adjusted audio signal of the digital radio broadcast, (b) the input signal changing means 15 converts the first input signal to the digital radio before the necessity of switching or always. It is also included that the audio signal is related to the broadcast adjustment audio signal. Thereby, at least when audio is switched between digital radio broadcast and analog radio broadcast, sudden change in sound quality due to mismatch of audio frequency characteristics related to audio of radio broadcast before and after switching can be avoided.

  The change of the first input signal from the original audio signal to the adjusted audio signal by the input signal changing unit 15 is preferably performed gradually rather than at once. However, a manual operation switch for audio frequency characteristic matching is provided, and as the user operates the manual operation switch for audio frequency characteristic matching, the first input signal is changed from the original audio signal to the adjusted audio signal. When changing, since the user is fully aware of the change, that is, even if there is a sudden change in sound quality, it does not give the user a significant psychological hit, so the first input signal from the original audio signal Changes to the adjusted audio signal can also be made at once. A specific method in which the input signal changing unit 15 gently changes the first input signal from the original audio signal to the adjusted audio signal is, for example, that the audio equalizer 12 does not generate the adjusted audio signal at a stroke after the operation starts. An intermediate signal is generated in which the audio frequency characteristic gradually changes from that of the original audio signal to that of the adjusted audio signal, and after the first input signal is switched to the output of the audio equalizer, The gradual change from the original audio signal to the adjusted audio signal.

  Audio switching between digital radio broadcasting and analog radio broadcasting includes not only switching from audio relating to digital radio broadcasting to audio relating to analog radio broadcasting, but also vice versa.

In the opposite case, that is, when switching from audio related to analog radio broadcast to audio related to digital radio broadcast, as well as switching from audio related to digital radio broadcast to audio related to analog radio broadcast, switch at the latest. Before the start of processing, the first input signal is changed from the original audio signal to the adjusted audio signal, and after the switching process is completed through the switching period, the reception quality of the digital radio broadcast is appropriately increased. The input signal is gradually changed from the adjusted audio signal to the original audio signal. As a method of gradually changing, specifically, the original audio fades in and the adjusted audio signal fades out, and the audio equalizer 12 gradually changes the audio frequency characteristic from that of the adjusted audio signal to that of the original audio signal. For example, a changing intermediate signal is generated, and the intermediate signal is used as the first input signal. However, in the case of switching from audio related to analog radio broadcasting to audio related to digital radio broadcasting, the switching period is shortened or the use of the adjustment audio signal Iu in the switching period is stopped, so that high-quality digital radio You may make it switch to the audio | voice which concerns on broadcast quickly.

  Thus, at the time of audio switching between digital radio broadcasting and analog radio broadcasting, the audio frequency characteristics of digital radio broadcasting and the audio frequency characteristics of analog radio broadcasting are in a consistent state, so that annoying sound quality change associated with switching is mitigated. As described with reference to FIG. 3, in IBOC radio broadcasting, the audio frequency characteristic has little difference between the audio frequency characteristic related to digital radio broadcast and the audio frequency characteristic related to FM analog radio broadcast. The difference between such audio frequency characteristics and audio frequency characteristics related to AM analog radio broadcasting is significant. Therefore, the power of audio frequency characteristic matching is greatly exhibited in audio switching between digital radio broadcasting and AM radio broadcasting.

A development type of the radio broadcast receiver 10 will be described. In the switching period of the selected audio signal, the audio signal selection unit 13 generates a mixed signal obtained by mixing the selected audio signals before and after switching as a selected audio signal, and the mixed signal is selected audio before and after switching. audio according to the signal is an audio signal to fade out and fade-in, respectively it in the audio output unit 14. By the fade-in and fade-out, the change in volume at the time of audio switching between digital radio broadcast and analog radio broadcast is alleviated.

  The radio broadcast receiver 10 can also be equipped with an operation member 21 for user selection. The user selection operation member 21 permits or allows the input changing unit 15 to change the first input signal from the original audio signal Id of the digital radio broadcast to the audio signal Iu related to the adjusted audio signal of the digital radio broadcast. Prohibit. In the radio broadcast receiver 10, the adjusted audio signal Iu is always replaced with the original audio signal Id during listening to the digital radio broadcast in order to match the audio frequency characteristics when the audio is switched between the digital radio broadcast and the analog radio broadcast. There is a case where audio related to is output. In such a case, when driving in an area where the radio field strength of digital radio broadcasting is sufficient so that switching does not occur, the user listens to audio with poor sound quality even though he is listening to audio of digital broadcasting. Will be. When the user is traveling in an area where switching does not occur frequently, the user can listen to the audio related to the high-quality original audio signal Id by operating the user selection operation member 21.

  The radio broadcast receiver 10 can also be equipped with variable amplification means 22. The variable amplifying means 22 amplifies the adjusted audio signal Iu of the digital radio broadcast with an amplification factor at which the level of the adjusted audio signal of the digital radio broadcast substantially matches the level of the second input signal.

  The amplification factor in the variable amplification means 22 includes 1 or less. An amplification factor of 1 or less means attenuation rather than amplification. The input signal changing unit 15 uses the audio signal related to the adjusted audio signal Iu of the digital radio broadcast as the output of the variable amplifying unit 22. When the output of the variable amplification means 22 is Iv, when the amplification factor of the variable amplification means 22 is 1, Iu = Iv. The volume of audio related to digital radio broadcasting is kept almost constant even when the electric field strength of received radio waves decreases, whereas the volume of audio related to analog radio broadcasting decreases as the electric field strength of received radio waves decreases. When the audio is switched between the digital radio broadcast and the analog radio broadcast, the sound volume changes suddenly. The variable amplification means 22 changes the amplification factor so as to match the volume of audio related to digital radio broadcasting with the volume of audio related to analog radio broadcast, so that a sudden change in volume during switching is alleviated.

  FIG. 5 is a flowchart of the radio broadcast receiver control method 50. The control method 50 for a radio broadcast receiver is configured to output audio corresponding to digital radio broadcast and analog radio broadcast according to the quality of received radio waves of the digital radio broadcast for digital radio broadcast and analog radio broadcast that are being performed simultaneously. This is a control method of the radio broadcast receiver 10 to be switched to. The radio broadcast receiver control method 50 has S51 to S57 and S59 as a basic configuration, and S65 and S66 as an advanced configuration.

  In the basic configuration of the control method 50 for a radio broadcast receiver, in S51 (quality detection step), the quality of the received radio wave of the digital radio broadcast is detected as the digital radio broadcast radio wave quality. An audio signal obtained by demodulating and decoding an RF signal related to digital radio broadcast is called an original audio signal Id of digital radio broadcast, and the audio frequency characteristic of digital radio broadcast matches the audio frequency characteristic of analog radio broadcast. A signal obtained by adjusting a signal level for each of a plurality of frequency band sections of the original audio signal Id of the digital radio broadcast is referred to as a digital audio broadcast adjusted audio signal Iu. In S52 (adjusted audio signal generation step), an adjusted audio signal Iu for digital radio broadcasting is generated. In S53, S54, S55, S56, and S57 (audio signal selection step), an audio signal obtained by demodulating an RF signal related to analog radio broadcasting using the original audio signal Id of digital radio broadcasting as the first input signal. When the analog radio broadcast demodulated audio signal Ia is a second input signal and the digital radio broadcast radio wave quality is equal to or higher than a predetermined level (determination of S56 is negative, determination of S53 is positive), the first input When the signal is (S54) and the digital radio broadcast radio wave quality is less than a predetermined level (determination of S53 is NO), the second input signal is (S55), and each is selected audio signal as an output signal. The selected audio signal is switched between the first and second input signals (the determination in S56 is positive and S57). In S59 (audio output step), the audio signal related to the selected audio signal is output as audio. In S61 (input signal changing step), before switching the selected audio signal in the audio signal selection step at the latest, the first input signal is changed from the original audio signal Id of the digital radio broadcast to the adjusted audio signal Iu of the digital radio broadcast. Change to audio signal.

In the developed version of the control method 50 for a radio broadcast receiver, in S57, in the switching period of the selected audio signal (determination in S56 is positive), a mixed signal obtained by mixing the selected audio signals before and after switching is selected as the selected audio signal. generated, the mixed signal is a audio signal the audio according to the pre-switching and selecting audio signal after switching fades out and fade-in, respectively it in the audio output means. Note that the fade-in and fade-out correspond to portions where output rates of Id and Ia in FIGS. 8 and 10 described later are inclined.

  In another development of the radio broadcast receiver control method 50, in S65 (input signal maintaining step), S61 (input change step) is performed based on the user selection in the user selection operation member 21 (the determination in S65 is positive). (If yes) is allowed and prohibited (if the determination in S65 is NO).

  In another development of the control method 50 for a radio broadcast receiver, in S66 (variable amplification step), the digital radio broadcast has an amplification factor at which the level of the adjusted audio signal of the digital radio broadcast substantially matches the level of the second input signal. Amplify broadcast adjustment audio signal. In S61, the audio signal related to the adjusted audio signal Iu of the digital radio broadcast is set as the amplified adjusted audio signal Iv in S66.

FIG. 6 is a configuration diagram of the IBOC radio 100 from the reception stage to the demodulation stage. The IBOC radio 100 is mounted on, for example, an automobile, and includes a digital radio broadcast side signal processing unit 101 and an analog radio broadcast side signal processing unit 102. The antenna 105 is provided as a common element of the digital radio broadcast side signal processing unit 101 and the analog radio broadcast side signal processing unit 102, and the RF signal of the IBOC received radio wave captured by the antenna 105 is the digital radio broadcast side signal processing unit 101. And the RF amplifier 136 of the analog radio broadcast side signal processing unit 102. The digital radio broadcast side signal processing unit 101 and the analog radio broadcast side signal processing unit 102 include elements having the same configuration and operation except that the RF signals to be processed are different. The same elements are the RF amplifier 106 and the RF amplifier 136, the mixer 107 and the mixer 137, the IF filter 108 and the IF filter 138, the IF amplifier 109 and the IF amplifier 139, the AGC circuit 120 and the AGC circuit 150, and the local oscillator 121 and the local oscillator. This is an oscillator 151. The IBOC demodulator 110 of the digital radio broadcast side signal processing unit 101 performs demodulation and decoding, whereas the demodulator 140 of the analog radio broadcast side signal processing unit 102 performs only demodulation. Instead of describing both the digital radio broadcast side signal processing unit 101 and the analog radio broadcast side signal processing unit 102, the digital radio broadcast side signal processing unit 101 is selected as a representative thereof, and the digital radio broadcast side signal processing unit 101 explain. The RF signal is amplified by the RF amplifier 106, mixed with the oscillation signal from the local oscillator 121 by the mixer 107, and converted into an IF (intermediate frequency) signal. The IF signal passes through the IF filter 108, is amplified by the IF amplifier 109, and is demodulated by the IBOC demodulator 110. The AGC circuit 120 controls the amplification factor of the RF amplifier 106 so that the output amplitude of the RF amplifier 106 is constant regardless of the input amplitude of the RF amplifier 106. The AGC circuit 122 controls the amplification factor of the IF amplifier 109 so that the output amplitude of the IF amplifier 109 is constant regardless of the input amplitude of the IF amplifier 109.

  FIG. 7 is a configuration diagram of an audio switching control stage of the IBOC radio 100. The audio equalizer 160 is interposed between the IBOC demodulator 110 and the blend control circuit 163, and generates a signal in which the signal level of the demodulated signal output from the IBOC demodulator 110 is adjusted for each of a plurality of frequency band sections. . The audio frequency characteristic adjustment signal generator 165 receives information on the audio frequency characteristics on the digital radio broadcast side signal processing unit 101 side and the analog radio broadcast side signal processing unit 102 side, and generates an audio frequency characteristic adjustment signal. The audio frequency characteristic adjustment signal is used by the audio equalizer 160 to determine the adjustment level of the signal level for each frequency band section. The blend control circuit 163 includes a blend signal generator 168, variable amplifiers 169 and 170, and an adder 171. The variable amplifier 169 amplifies the audio signal from the audio equalizer 160, the variable amplifier 170 amplifies the audio signal from the demodulator 140, and the adder 171 adds the audio signals from the variable amplifiers 169 and 170. The addition signal of the adder 171 is sent to a speaker (not shown) through a power amplifier whose amplification factor is controlled by a user operation. The blend signal generator 168 receives the audio switching signal between the digital radio broadcast and the analog radio broadcast, and controls the amplification factors of the variable amplifiers 169 and 170 based on the signal. The amplification factors of the variable amplifiers 169 and 170 are 1 or less, and the variable amplifiers 169 and 170 are substantially attenuators.

  FIG. 8 is a graph showing changes in the input / output signals of the blend control circuit 163 with respect to a predetermined level change of the received signal in the IBOC radio 100. Now, suppose that an automobile equipped with the IBOC radio 100 gradually moves away from the IBOC broadcasting station. In this case, the received signal level of the IBOC decreases with time as shown in FIG. Ia as the output of the demodulator 140 gradually decreases from time t1. Also, since it becomes difficult to decode an RF signal related to digital radio broadcasting at time t4, Id as an output of the IBOC demodulator 110 becomes zero at a time at time t4. From time t2 to t3 is a switching period in which the audio output from the speaker is switched from audio related to digital radio broadcast to audio related to analog radio broadcast. Here, it is assumed that the output of the blend control circuit 163 is defined as Io, and Io is composed of portions Ido and Iao related to the output signals Id and Ia of the IBOC demodulator 110 and the demodulator 140 (Io = Ido + Iao). The output rates for Id and Ia are defined as Ido / Id and Iao / Ia.

  In this example, the audio equalizer 160 is not limited to a predetermined time before the audio switching between the digital radio broadcast and the analog radio broadcast, and always operates. The audio equalizer 160 changes the signal level for each frequency band section of Id and matches the audio frequency characteristic of the digital radio broadcast side signal processing unit 101 with the audio frequency characteristic of the analog radio broadcast side signal processing unit 102. The output signal of the audio equalizer 160 is slightly lower than Id. This is because, as can be seen from FIG. 3, the audio frequency characteristics of the analog radio broadcast side signal processing unit 102 are lower than the audio frequency characteristics of the digital radio broadcast side signal processing unit 101 at both ends thereof. This is because the level of the frequency band section at both ends of Id is lowered by the audio equalizer 160 when the audio frequency characteristics are matched with the audio frequency characteristics of the signal processing unit 102 on the analog radio broadcast side. However, since the amount of decrease in Id is small, in FIG. 8, the output rate of Id is expressed as being constant between t1 and t2.

  The variable amplifier 169 of the blend control circuit 163 linearly changes the amplification factor from 1 at time t2 to 0 at time t3. As a result, the output rate of Id is approximately 1 until time t2, but gradually decreases from time t2, and becomes 0 after time t3. On the other hand, the variable amplifier 170 of the blend control circuit 163 linearly changes the amplification factor from 0 at time t2 to 1 at time t3. As a result, the output rate of Ia was 0 until time t2, but gradually increased from time t2, and becomes 1 after time t3. Such a change in the output rate of Id and Ia appears as an audio fade-out related to Id and an audio fade-in related to Ia in the speaker. With respect to Io as an output of the radio broadcast receiver 103, the total amount is Ido from time t2 to time I2 and Iao from time t2 to time t3. The ratio of Id to Ia in this mixing is the time As the course progresses, the former decreases and the latter increases. The total amount of Io is Iao after time t3.

  At time t2, the level of Ia is already lower than the level of Id, and immediately after time t2, the output of the adder 171 suddenly drops as shown by A. This leads to a sudden change in volume from the speaker. However, in the IBOC radio 100, the audio frequency characteristic of the digital radio broadcast and the audio frequency characteristic of the analog radio broadcast are matched by the operation of the audio equalizer 160. Despite the appearance, the change in sound quality is alleviated and the user's discomfort is reduced.

  FIG. 9 is a configuration diagram of the main part of another IBOC radio 180. The IBOC radio 180 is an improvement over the IBOC radio 100 and suppresses the appearance of A in FIG. Regarding the IBOC radio 180, the same elements as those of the IBOC radio 100 are designated by the same reference numerals, description thereof will be omitted, and differences will be described. In the IBOC radio 180, an audio level adjustment signal generator 181 and a variable amplifier 182 are added to the IBOC radio 100. The variable amplifier 182 is interposed between the audio equalizer 160 and the variable amplifier 169 of the blend control circuit 163, amplifies the output of the audio equalizer 160 (because the amplification factor is 1 or less, attenuates), and blend control. Send to circuit 163. The audio level adjustment signal generator 181 receives information on the amplitude (audio level) at each time point of the demodulator 140 and controls the amplification factor of the variable amplifier 182 based on this information. As a result, the Iv level and Ia level of the output of the variable amplifier 182 are matched.

  FIG. 10 is a graph showing changes in input / output signals and the like of the blend control circuit 163 with respect to a predetermined level change of the received signal in the IBOC radio 180. The reception signal level of IBOC is the same as in FIG. In the IBOC radio 180, the variable amplifier 182 controls the output amplitude of the audio equalizer 160 to be the output amplitude of the demodulator 140 from the time t 1 before the time t 2 before the audio signal is switched in the blend control circuit 163. The process of amplifying the output of the audio equalizer 160 (attenuating because this amplification factor is 1 or less) is started while changing the amplification factor so as to match. This process is continuously performed until time t3 when the switching process in the blend control circuit 163 ends. As a result, the input-side audio signal of the variable amplifier 169 of the blend control circuit 163 has the same amplitude as the input-side audio signal of the variable amplifier 170, and the output Io of the blend control circuit 163 does not suddenly change as shown in FIG. However, it decreases gradually.

  In the IBOC radio 180, in addition to the audio frequency characteristic matching by the audio equalizer 160, the amplitude matching by the variable amplifier 182 is also performed, so that the audio discomfort at the time of switching between digital radio broadcasting and analog radio broadcasting is greatly reduced. .

It is a figure which shows the power spectrum in FM-IBOC system radio broadcasting. It is a figure which shows the power spectrum in AM-IBOC system radio broadcasting. The audio frequency characteristics of each broadcast format in IBOC are shown in comparison. It is a block diagram of a radio broadcast receiver. It is a flowchart of the control method for radio broadcast receivers. It is a block diagram from the receiving stage to the demodulation stage of the IBOC radio. It is a block diagram of the audio switching control stage of the IBOC radio. It is a graph which shows the change of the input / output signal etc. of a blend control circuit with respect to the predetermined level change of a received signal in the radio for IBOC. It is a block diagram of the principal part of another IBOC radio. It is a graph which shows the change of the input / output signal etc. of a blend control circuit with respect to the predetermined level change of a received signal in the radio | wire for IBOC.

Explanation of symbols

10: Radio broadcast receiver, 11: Quality detection means, 12: Audio equalizer, 13: Audio signal selection means, 14: Audio output means, 15: Input signal changing means, 21: User selection operation member, 22: Variable amplification means.

Claims (8)

In a radio broadcast receiver that switches output audio to audio related to digital radio broadcast and analog radio broadcast according to the quality of received radio waves of the digital radio broadcast for digital radio broadcast and analog radio broadcast that are being performed simultaneously ,
Quality detection means for detecting the received radio wave quality of the digital radio broadcast as a digital radio broadcast radio wave quality;
The audio signal obtained by demodulating and decoding the RF signal related to the digital radio broadcast is called an original audio signal of the digital radio broadcast, and the audio frequency characteristic of the digital radio broadcast is changed to the audio frequency characteristic of the analog radio broadcast. A signal obtained by adjusting a signal level for each of a plurality of frequency band sections of the original audio signal of the digital radio broadcast so as to be matched is referred to as an adjusted audio signal of the digital radio broadcast, and the adjusted audio signal of the digital radio broadcast Produce an audio equalizer,
The original audio signal of the digital radio broadcast is used as a first input signal, and the demodulated audio signal of the analog radio broadcast as an audio signal obtained by demodulating the RF signal related to the analog radio broadcast is used as a second input signal. And when the digital radio broadcast radio wave quality is equal to or higher than a predetermined level, the first input signal, and when the digital radio broadcast radio wave quality is lower than a predetermined level, the second input signal is set respectively. An audio signal selection means for switching the selected audio signal between the first and second input signals, as a selected audio signal as an output signal;
Audio output means for outputting audio related to the selected audio signal, and before switching of the selected audio signal in the audio signal selection means at the latest, the first input signal is changed from the original audio signal of the digital radio broadcast to the digital Input signal changing means for changing to an audio signal related to a radio audio adjustment audio signal;
Have
The input signal changing means is a period when the audio signal selecting means switches the selected audio signal from the first input signal to the second input signal, and the first input signal is changed to the original audio signal. In a first period of changing from a signal to an audio signal related to the adjusted audio signal, an intermediate signal whose audio frequency characteristics gradually change from that of the original audio signal to that of the adjusted audio signal is generated, The audio signal is the first input signal,
The input signal changing means is a period when the audio signal selecting means switches the selected audio signal from the second input signal to the first input signal, and the first input signal is changed to the adjusted audio. In the second period in which the audio signal related to the signal is changed from the original audio signal to the original audio signal, an intermediate signal in which the audio frequency characteristic gradually changes from that of the adjusted audio signal to that of the original audio signal is generated, The audio signal is the first input signal,
The radio broadcast receiver characterized in that the input signal changing means makes the second period shorter than the first period. The audio signal selection means generates a mixed signal obtained by mixing the selected audio signals before and after switching as a selected audio signal in the switching period of the selected audio signal, and the mixed signal is selected audio before and after switching. 2. The radio broadcast receiver according to claim 1 , wherein the audio associated with the signal is an audio signal that fades out and fades in the audio output means. User selection operation member for allowing or prohibiting, by user selection, the input changing means to change the first input signal from the original audio signal of the digital radio broadcast to an audio signal related to the adjusted audio signal of the digital radio broadcast. ,
The radio broadcast receiver according to claim 1, further comprising: Variable amplification means for amplifying the digital radio broadcast adjustment audio signal at an amplification factor at which the level of the adjustment radio signal of the digital radio broadcast substantially matches the level of the second input signal, and the adjustment audio of the digital radio broadcast The input signal changing means for making the audio signal related to the signal an output of the variable amplifying means;
The radio broadcast receiver according to claim 1, comprising: Radio broadcast receivers that switch output audio to digital radio broadcast and analog radio broadcast audio according to the quality of received radio waves of the digital radio broadcast for digital radio broadcasts and analog radio broadcasts that are being conducted simultaneously In the control method,
A quality detection step of detecting the received radio wave quality of the digital radio broadcast as a digital radio broadcast radio wave quality;
The audio signal obtained by demodulating and decoding the RF signal related to the digital radio broadcast is called an original audio signal of the digital radio broadcast, and the audio frequency characteristic of the digital radio broadcast is changed to the audio frequency characteristic of the analog radio broadcast. A signal obtained by adjusting a signal level for each of a plurality of frequency band sections of the original audio signal of the digital radio broadcast so as to be matched is referred to as an adjusted audio signal of the digital radio broadcast, and the adjusted audio signal of the digital radio broadcast Adjusting audio signal generation step,
The original audio signal of the digital radio broadcast is used as a first input signal, and the demodulated audio signal of the analog radio broadcast as an audio signal obtained by demodulating the RF signal related to the analog radio broadcast is used as a second input signal. And when the digital radio broadcast radio wave quality is equal to or higher than a predetermined level, the first input signal, and when the digital radio broadcast radio wave quality is lower than a predetermined level, the second input signal is set respectively. An audio signal selection step of selecting a selected audio signal as an output signal and switching the selected audio signal between the first and second input signals;
An audio output step of outputting audio related to the selected audio signal from an audio output means, and at least before switching of the selected audio signal in the audio signal selection step, the first input signal is converted to the original audio of the digital radio broadcast An input signal changing step for changing from a signal to an audio signal related to the adjusted audio signal of the digital radio broadcast;
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In the input signal changing step, the selected audio signal is switched from the first input signal to the second input signal, and the first input signal is changed from the original audio signal to the adjusted audio signal. In the first period in which the audio signal is changed to an audio signal related to the intermediate signal, an intermediate signal whose audio frequency characteristic gradually changes from that of the original audio signal to that of the adjusted audio signal is generated, and the audio signal related to the intermediate signal is changed to the first audio signal. Input signal,
In the input signal changing step, a period when the selected audio signal is switched from the second input signal to the first input signal, wherein the first input signal is changed from the audio signal related to the adjusted audio signal. In the second period of changing to the original audio signal, an intermediate signal whose audio frequency characteristic gradually changes from that of the adjusted audio signal to that of the original audio signal is generated, and the audio signal related to the intermediate signal is changed to the first audio signal. Input signal,
The method of controlling a radio broadcast receiver, wherein, in the input signal changing step, the second period is shorter than the first period.   The audio signal selection step generates a mixed signal obtained by mixing the selected audio signals before and after switching as a selected audio signal in the switching period of the selected audio signal, and the mixed signal is selected audio before and after switching. 6. The method of controlling a radio broadcast receiver according to claim 5, wherein the audio associated with the signal is an audio signal that fades out and fades in the audio output means. An input change control step for allowing and prohibiting the execution of the input change step based on a user selection in the user selection operation member;
The method of controlling a radio broadcast receiver according to claim 5 or 6, characterized by comprising: A variable amplification step of amplifying the digital radio broadcast adjustment audio signal at an amplification factor that substantially matches the level of the digital radio broadcast adjustment audio signal, and the digital radio broadcast adjustment audio; The input signal changing step, wherein the audio signal related to the signal is an amplification adjustment audio signal in the variable amplification step;
The method for controlling a radio broadcast receiver according to claim 5, wherein:

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