Broadcast receiver and broadcast reception method

Abstract

The present invention provides a broadcast receiver and a broadcast reception method that make it possible to reduce a sense of incongruity felt by a viewer when switching between an analog broadcast wave and a digital broadcast wave. This broadcast receiver comprises: a digital demodulation unit that receives a first clock signal from a first clock source and outputs a digital audio signal obtained by demodulating a digital broadcast; an analog demodulation unit that receives a second clock signal from a second clock source and outputs an analog audio signal obtained by demodulating an analog broadcast; a calculation unit that calculates a correlation value indicating a correlation between the digital audio signal and the analog audio signal, and calculates a time difference between the digital audio signal and the analog audio signal on the basis of the correlation value; and a synchronization unit that synchronizes the digital audio signal and the analog audio signal on the basis of the time difference. The calculation unit evaluates either the digital broadcast and the analog broadcast or the digital audio signal and the analog audio signal, and changes at least one of the process of calculating the correlation value and the process of calculating the time difference according to the result of the evaluation.

Description

Broadcast receiver and broadcast receiving method

[0001] The present invention relates to a broadcast receiver and a broadcast receiving method.

[0002] In recent years, radio broadcasting using In-band on-channel (IBOC), which transmits analog and digital broadcasts of the same content over the same frequency band, has become widespread. In IBOC radio broadcasting, analog and digital broadcasts are mixed and output, or the analog and digital broadcasts are switched between for output.

[0003] Here, there is a time difference between the analog broadcast waves that transmit analog broadcasts and the digital broadcast waves that transmit digital broadcasts, and such a difference can cause information to be lost or overlapped when switching between the analog broadcast waves and the digital broadcast waves. Patent Document 1 describes a technology that calculates the time difference between the analog broadcast waves and the digital broadcast waves by correlating the analog broadcast waves with the digital broadcast waves and corrects the time difference.

[0004] Japanese Patent Application Laid-Open No. 2006-295662

[0005] However, depending on the state of the audio signals of the analog and digital broadcast waves, it may be difficult to calculate the correlation between the analog and digital broadcast waves, and as a result, it may not be possible to correct the time difference between the analog and digital broadcast waves.

[0006] One aspect of the disclosed technology aims to provide a broadcast receiver and a broadcast receiving method that can reduce the sense of discomfort that viewers feel when switching between analog broadcast waves and digital broadcast waves.

[0007] One aspect of the disclosed technology is exemplified by the following broadcast receiver: This broadcast receiver is a broadcast receiver that receives digital broadcast waves and analog broadcast waves having the same content. This broadcast receiver comprises a digital demodulation unit that receives a first clock signal from a first clock source, demodulates the digital broadcast wave to generate a digital audio signal, and outputs the digital audio signal; an analog demodulation unit that receives a second clock signal from a second clock source, demodulates the analog broadcast wave to generate an analog audio signal, and outputs the analog audio signal; a calculation unit that calculates a correlation value indicating the correlation between the digital audio signal and the analog audio signal and calculates a time difference between the digital audio signal and the analog audio signal based on the correlation value; a synchronization unit that synchronizes the digital audio signal and the analog audio signal based on the time difference; and a control unit that evaluates either the digital broadcast wave and the analog broadcast wave or the digital audio signal and the analog audio signal, and causes the synchronization unit to perform the synchronization if the result of the evaluation indicates that the time difference can be calculated normally, and does not cause the synchronization unit to perform the synchronization if the result of the evaluation indicates that the time difference cannot be calculated normally.

[0008] According to the disclosed technology, it is possible to reduce the sense of discomfort felt by viewers when switching between analog broadcast waves and digital broadcast waves.

[0009] Fig. 1 is a diagram illustrating an example of a broadcast receiver according to an embodiment. Fig. 2 is a diagram illustrating an example of a case where a digital audio signal and an analog audio signal are periodic signals. Fig. 3 is a diagram illustrating an example of a processing flow of the broadcast receiver according to an embodiment.

[0010] <Embodiments> An embodiment will now be described with reference to the drawings. FIG. 1 is a diagram showing an example of a broadcast receiver 1 according to an embodiment. The broadcast receiver 1 is an IBOC-compatible broadcast receiver that receives analog and digital broadcast waves having the same content. The broadcast receiver 1 may be, for example, an in-vehicle broadcast receiver that is installed in a passenger vehicle and allows passengers to listen to radio broadcasts. The broadcast receiver 1 includes a clock supply unit 2, a clock supply unit 3, a digital demodulation unit 4, an analog demodulation unit 5, a filter 6, and a control unit 7.

[0011] The clock supply unit 2 is a clock source that supplies a clock signal to the digital demodulation unit 4. The clock supply unit 3 is a clock source that supplies a clock signal to the analog demodulation unit 5. The clock supply units 2 and 3 generate clock signals independently of each other. In other words, the clock signal supplied by the clock supply unit 2 and the clock signal supplied by the clock supply unit 3 are not synchronized. The clock supply unit 2 is an example of a "first clock source." The clock supply unit 3 is an example of a "second clock source."

[0012] The digital demodulation unit 4 is a circuit that demodulates digital broadcast waves. The digital demodulation unit 4 receives a clock signal from the clock supply unit 2, demodulates the digital broadcast waves, and outputs a digital audio signal obtained by demodulating the digital broadcast waves. The analog demodulation unit 5 demodulates the analog broadcast waves and outputs an analog audio signal obtained by demodulating the analog broadcast waves. The analog demodulation unit 5 receives a clock signal from the clock supply unit 3, and executes demodulation processing of the analog broadcast waves. In other words, the digital demodulation unit 4 and the analog demodulation unit 5 receive clock signals from different clock sources.

[0013] The filter 6 performs filtering to match the frequency characteristics of the digital audio signal demodulated by the digital demodulation unit 4 and the analog audio signal demodulated by the analog demodulation unit 5. For example, even if the digital audio signal and the analog audio signal contain the same audio data, the waveforms often differ in the high frequency band. Therefore, a filter that removes such high frequency bands is used as the filter 6. Examples of filters that remove such high frequency bands include a low-pass filter and a band-pass filter. The range of the high frequency band removed by the filter 6 is determined as appropriate, for example, during manufacturing tests of the broadcast receiver 1.

[0014] The control unit 7 calculates a correction amount for correcting a time lag between the digital audio signal and the analog audio signal filtered by the filter 6, and selects an audio signal to be output. The control unit 7 includes, for example, a processor and a memory, and performs processes as a correction amount calculation unit 71, a determination unit 72, a synchronization unit 73, and a selection unit 74 by the processor executing a program stored in the memory.

[0015] The correction amount calculation unit 71 calculates a correction amount for synchronizing the digital audio signal filtered by the filter 6 with the analog audio signal. The broadcast receiver 1 receives digital broadcast waves and analog broadcast waves with the same content, but because the processing time for the demodulation process by the digital demodulation unit 4 and the processing time for the demodulation process by the analog demodulation unit 5 are different, a time lag occurs between the demodulated digital audio signal and the analog audio signal. Therefore, the correction amount calculation unit 71 calculates a correction amount for eliminating the time lag between the digital audio signal and the analog audio signal and synchronizing them. The correction amount is an example of a "time difference."

[0016] The correction amount calculation unit 71 may, for example, calculate a correlation value indicating the correlation between the digital audio signal and the analog audio signal, and use the position of the highest correlation value as a reference to determine the deviation between the digital audio signal and the analog audio signal as the correction amount. The correction amount calculation unit 71 may, for example, calculate a cross-correlation function between the digital audio signal and the analog audio signal. Then, the correction amount calculation unit 71 may determine the time at which a peak appears in the calculated cross-correlation function as the time difference between the digital audio signal and the analog audio signal. The correction amount calculation unit 71 may then use the determined time difference as the correction amount. For example, if the peak in the cross-correlation function indicates a delay of 2 seconds between the analog audio signal and the digital audio signal, the correction amount calculation unit 71 may set the correction amount to "-2 seconds."

[0017] The determination unit 72 determines whether or not to apply the correction amount calculated by the correction amount calculation unit 71 based on the evaluation results of the digital audio signal and the analog audio signal. Examples of evaluations by the determination unit 72 include evaluation of the waveforms of the digital audio signal and the analog audio signal and evaluation of the signal strength. Examples of waveform evaluations include whether or not the waveforms of the digital audio signal and the analog audio signal are periodic. Whether or not the waveforms of the digital audio signal and the analog audio signal are periodic can be determined, for example, by the appearance of substantially the same peak values ​​at multiple locations within a predetermined period in a cross-correlation function. Examples of signal strength evaluations include whether or not the signal strengths of the digital audio signal and the analog audio signal are equal to or less than a predetermined threshold.

[0018] For example, a case where the determination unit 72 makes a negative determination can be when the digital audio signal and the analog audio signal are periodic signals. FIG. 2 is a diagram illustrating an example where the digital audio signal and the analog audio signal are periodic signals. The upper part of FIG. 2 illustrates an example of a waveform of a digital audio signal, and the lower part illustrates an example of a waveform of an analog audio signal. Assume that position P11 in the digital audio signal illustrated in FIG. 2 and positions P21, P22, and P23 in the analog audio signal have approximately the same peak value. In such a case, when the cross-correlation function between the digital audio signal and the analog audio signal is calculated, multiple peaks showing approximately the same value appear in the cross-correlation function. When peaks showing approximately the same value appear at multiple positions in the cross-correlation function, the correction amount calculation unit 71 cannot uniquely determine the correction amount. The determination unit 72 may make a negative determination when multiple approximately identical correlation values ​​exist within a predetermined period, as in the case where the digital audio signal and the analog audio signal have periodic waveforms.

[0019] Another example of a case in which the determination unit 72 makes a negative determination is when the signal strengths of the digital audio signal and the analog audio signal are equal to or less than a predetermined threshold. When the signal strengths of the digital audio signal and the analog audio signal are equal to or less than the predetermined threshold, noise tends to become relatively large. Because there is no correlation between the noise of the digital audio signal and the noise of the analog audio signal, a peak indicating a high correlation value may not clearly appear when the noise becomes relatively large. Therefore, the determination unit 72 makes a negative determination, for example, when the signal strengths of the digital audio signal and the analog audio signal are equal to or less than a predetermined threshold. Alternatively, the determination unit 72 may make a positive determination, for example, when the digital audio signal and the analog audio signal are non-periodic signals and when the signal strengths of the digital audio signal and the analog audio signal are greater than a predetermined threshold. When the determination unit 72 makes a negative determination, it causes the correction amount calculation unit 71 to calculate the correction amount again. When the determination unit 72 makes a positive determination, it instructs the synchronization unit 73 to perform correction using the correction amount calculated by the correction amount calculation unit 71.

[0020] The synchronization unit 73 synchronizes the digital audio signal and the analog audio signal using the correction amount calculated by the correction amount calculation unit 71. For example, when the correction amount indicates that the digital audio signal is delayed by two seconds and the output is switched from the digital audio signal to the analog audio signal, the synchronization unit 73 may set the analog audio signal to be output at the time of switching to the audio signal two seconds before the time of switching.

[0021] The selection unit 74 selects the audio signal to be output to an audio output device such as a speaker connected to the broadcast receiver 1 from among a digital audio signal, an analog audio signal, and a mixed signal of a digital audio signal and an analog audio signal. For example, the selection unit 74 may select the audio signal with the better reception status from the digital audio signal and the analog audio signal. When the reception status of both the digital audio signal and the analog audio signal is good, the selection unit 74 may select the digital audio signal with the higher sound quality. Furthermore, the selection unit 74 may receive an instruction from the user as to which audio signal to select from the digital audio signal and the analog audio signal.

[0022] Furthermore, when switching the audio signal to be selected from a digital audio signal to an analog audio signal, the selection unit 74 may select the mixed signal before selecting the analog audio signal. Furthermore, when switching the audio signal to be selected from an analog audio signal to a digital audio signal, the selection unit 74 may select the mixed signal before selecting the digital audio signal. By selecting the mixed signal, the sense of discomfort felt by the viewer when switching between the digital audio signal and the analog audio signal is reduced.

[0023] <Processing Flow> Fig. 3 is a diagram showing an example of a processing flow of the broadcast receiver 1 according to the embodiment. Fig. 3 illustrates a processing flow for synchronizing a digital audio signal and an analog audio signal. Hereinafter, an example of the processing flow of the broadcast receiver 1 will be described with reference to Fig. 3.

[0024] In step S1, the digital demodulation unit 4 demodulates the received digital broadcast wave to generate a digital audio signal. Also, the analog demodulation unit 5 demodulates the received analog broadcast wave to generate an analog audio signal. The processing by the digital demodulation unit 4 in step S1 is an example of "digital demodulation processing." The processing by the analog demodulation unit 5 in step S1 is an example of "analog demodulation processing."

[0025] In step S2, the filter 6 performs filtering on the digital and analog audio signals demodulated in step S1.

[0026] In step S3, the correction amount calculation unit 71 calculates a correlation value between the digital audio signal and the analog audio signal that have been filtered in step S2, and calculates a correction amount based on the calculated correlation value. The process of calculating the correlation value by the correction amount calculation unit 71 in step S3 is an example of a "calculation process."

[0027] In step S4, the determination unit 72 determines whether or not to apply the correction amount calculated in step S3. If the correction amount is to be applied (positive determination in step S4), the process proceeds to step S5. If the correction amount is not to be applied (negative determination in step S4), the process returns to step S3. That is, the synchronization between the digital audio signal and the analog audio signal by the synchronization unit 73 is stopped.

[0028] In step S5, the synchronization unit 73 synchronizes the digital audio signal and the analog audio signal based on the correction amount calculated in step S3. The process by the synchronization unit 73 in step S5 is an example of a "synchronization process."

[0029] In step S6, the selection unit 74 selects the audio signal to be output to the audio output device from among a digital audio signal, an analog audio signal, and a mixed signal of a digital audio signal and an analog audio signal.

[0030] <Effects of the embodiment> According to the present embodiment, if an appropriate correction amount cannot be determined, such as when a unique correction amount cannot be determined or when the signal strengths of the digital audio signal and the analog audio signal are below a predetermined threshold, the synchronization of the digital audio signal and the analog audio signal by the synchronization unit 73 using the correction amount calculated by the correction amount calculation unit 71 is stopped. Even if an attempt is made to synchronize the digital audio signal or the analog audio signal based on an incorrect correction amount, proper synchronization cannot be achieved, and there is a risk that the discomfort felt by listeners of radio when switching between the digital audio signal and the analog audio signal will increase. According to the present embodiment, synchronization due to an incorrect correction amount is suppressed, thereby reducing the discomfort felt by users listening to radio broadcasts.

[0031] <Modification> In the embodiment described above, filtering is performed by the filter 6, but the filter 6 may be omitted. However, filtering by the filter 6 improves the accuracy of calculating the correlation value between the digital audio signal and the analog audio signal.

[0032] In the embodiment described above, if an appropriate correction amount cannot be determined, the synchronization process by the synchronization unit 73 is stopped. However, if an appropriate correction amount cannot be determined, not only is the synchronization process by the synchronization unit 73 stopped, but calculation of the correction amount by the correction amount calculation unit 71 may also be stopped. By not calculating the correction amount, synchronization process by the synchronization unit 73 using an inappropriate correction amount is also stopped. Ultimately, this can reduce the sense of discomfort felt by users listening to radio broadcasts.

[0033] In the embodiment described above, the determination unit 72 evaluates digital audio signals and analog audio signals, but the determination unit 72 may also evaluate the levels (reception strength) of digital broadcast waves and analog broadcast waves, for example.

[0034] The embodiments and modifications disclosed above can be combined with each other.

[0035] REFERENCE SIGNS LIST 1 broadcast receiver 2 clock supply unit 3 clock supply unit 4 digital demodulation unit 5 analog demodulation unit 6 filter 7 control unit 71 correction amount calculation unit 72 determination unit 73 synchronization unit 74 selection unit

Claims

1. A broadcast receiver that receives digital broadcast waves and analog broadcast waves of the same content, comprising: a digital demodulation unit that receives a first clock signal from a first clock source, demodulates the digital broadcast waves to generate a digital audio signal, and outputs the digital audio signal; an analog demodulation unit that receives a second clock signal from a second clock source, demodulates the analog broadcast waves to generate an analog audio signal, and outputs the analog audio signal; a calculation unit that calculates a correlation value that indicates the correlation between the digital audio signal and the analog audio signal, and calculates a time difference between the digital audio signal and the analog audio signal based on the correlation value; a synchronization unit that synchronizes the digital audio signal and the analog audio signal based on the time difference; and a control unit that evaluates either the digital broadcast waves and the analog broadcast waves, or the digital audio signal and the analog audio signal, and causes the synchronization unit to perform the synchronization if the result of the evaluation indicates that the time difference can be calculated normally, and does not cause the synchronization unit to perform the synchronization if the result of the evaluation indicates that the time difference cannot be calculated normally.

2. The broadcast receiver of claim 1, wherein the control unit evaluates the signal strength of at least one of the digital broadcast and the analog broadcast, or the digital audio signal and the analog audio signal, and if the signal strength is equal to or greater than a threshold, causes the synchronization unit to perform processing to synchronize the digital audio signal and the analog audio signal, and if the signal strength is less than the threshold, does not cause the synchronization unit to perform processing to synchronize the digital audio signal and the analog audio signal.

3. The broadcast receiver of claim 1, wherein the control unit evaluates the correlation value between the digital audio signal and the analog audio signal calculated by the calculation unit, and if the correlation value has one peak that exceeds a threshold within a predetermined time interval, causes the synchronization unit to perform processing to synchronize the digital audio signal and the analog audio signal, and if the correlation value has two or more peaks that exceed a threshold within the predetermined time interval, does not cause the synchronization unit to perform processing to synchronize the digital audio signal and the analog audio signal.

4. A broadcast receiving method in which a broadcast receiver receives digital broadcast waves and analog broadcast waves of the same content, and performs the following steps: a digital demodulation process in which a first clock signal is received from a first clock source to demodulate the digital broadcast waves to generate a digital audio signal, and output the digital audio signal; an analog demodulation process in which a second clock signal is received from a second clock source to demodulate the analog broadcast waves to generate an analog audio signal, and output the analog audio signal; a calculation process in which a correlation value indicating the correlation between the digital audio signal and the analog audio signal is calculated, and a synchronization process in which the digital audio signal and the analog audio signal are synchronized based on the time difference; and a control process in which either the digital broadcast waves and the analog broadcast waves, or the digital audio signal and the analog audio signal, are evaluated, and if the result of the evaluation indicates that the time difference can be calculated correctly, the synchronization process is executed, and if the result of the evaluation indicates that the time difference cannot be calculated correctly, the synchronization process is not executed.

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