Patent Publication Number: US-8121566-B2

Title: Broadcast receiver and broadcast channel seek method

Description:
FIELD OF THE INVENTION 
     The present invention relates to a broadcasting receiver and a method for seeking broadcasting channel, in particular, to a broadcasting receiver suitable for receiving digital broadcasting, analog broadcasting and digital/analog hybrid broadcasting, and its method for seeking broadcasting channel. 
     BACKGROUND OF THE ART 
     Recently, it has become popular to process and manage the sound and video in digital format in appliances such as acoustic appliances and video appliances. Such trends in digital encoding of sound and video in appliances such as acoustic appliances are extending to the field of radio broadcasting. For example, in the United States, a digital radio broadcasting system called IBOC (In Band On Channel) is proposed and made available by iBiquity Digital Corp. 
     Meanwhile, conventional analog radio broadcasting broadcasts via carrier wave (hereinafter referred to as “analog carrier wave”) that has frequency distribution inside the frequency band (hereinafter referred to as “channel” or “frequency channel”) assigned to individual broadcasting stations. Actually, in order to avoid the interference between analog carrier wave of adjacent channels, only the center portion of the assigned band is used for the transmission of the analog carrier wave, and other portions are not used. It is noted that “digital radio broadcasting” in this application means “IBOC digital radio broadcasting”. 
     IBOC is a type of digital radio broadcasting that uses a frequency channel assigned to the conventional analog radio broadcasting. In IBOC standard, a plurality of signal formats are defined, such as a hybrid format in which the digital radio broadcasting signal is multiplexed onto the conventional analog radio broadcasting signal, and an all-digital format constituted by only digital signals, and it is designed to gradually transfer from conventional analog radio broadcasting to all-digital radio broadcasting that has many functions and is high in quality. In the IBOC, digital broadcasting signals are transmitted with Orthogonal Frequency Division Multiplexing (OFDM) that uses many carrier waves (subcarriers). 
     In the IBOC standard, a signal format called “hybrid format” is used in the transition period from analog broadcasting to all-digital broadcasting. In the hybrid format, the digital radio broadcasting, which allocates the subcarrier of digital broadcasting in the portion that is adjacent to the center portion of the band that the analog carrier wave uses and that was not conventionally used (hereinafter referred to as “sideband”) is broadcast using the modulated wave of the sideband of the band. In other words, in accordance with the hybrid format of the IBOC, the frequency band assigned for the conventional analog radio broadcasting is utilized effectively, and the analog radio broadcasting and the digital radio broadcasting are simultaneously transmitted using a same channel. 
     For example, Japanese Patent Provisional Publication No. JP2005-191850A (hereinafter referred to as “the Reference Document”) discloses an IBOC broadcasting receiver that is capable of receiving such IBOC digital radio broadcasting. The IBOC broadcasting receiver disclosed in the Reference Document is provided with an automatic seek function for seeking receivable channel. 
     The IBOC broadcasting receiver starts channel seeking operation when a predetermined user operation (e.g., pressing down once the “Tuning up” or “Tuning down” button equipped at the operation panel.) is performed, and the receiving intensity of the seeking channel is detected. When it is set in a first seek mode, the IBOC broadcasting receiver determines the channel station-existent if the detected receiving intensity is higher than a predetermined amount, and selects the channel, and the channel seeking operation is ceased. Further, when it is set in a second seek mode, the broadcasting receiver performs the decoding process of the digital broadcasting signal along with the channel seeking operation. Then, referring to the result of the process, it determines whether the digital radio broadcasting is performed in the channel. Only when it is determined that the digital radio broadcasting is performed, the channel is selected and the channel seeking operation is ceased. Thereby, the digital radio broadcasting is played. 
     DISCLOSURE OF THE INVENTION 
     However, the decoding and determining process is performed not only on the channel where it includes digital broadcasting signal but on the channel where the digital broadcasting is not performed, such as a channel including only the analog broadcasting signal or, a channel determined erroneously as station-existent (i.e., a state where a broadcasting station is found) due to the existence of strong noise, regardless of the fact that it is actually station-non-existent (i.e., a state where a broadcasting station is not found). Since the decoding process on the digital broadcasting is a time-lengthy process, there is a problem that such broadcasting receiver takes long time in the channel seeking operations. Further, in such a broadcasting receiver, it is possible to determine station-existence in a relatively simple arrangement by performing the station-existence determination only by judging presence/absence of a carrier wave of the analog broadcasting signal having a high signal intensity. However, if the station-existence determination is done only with the presence/absence of the carrier wave of the analog broadcasting signal, there is a problem that the frequency channel in which the broadcasting with the all-digital format where the intensity of the carrier wave is week is erroneously determined to be station-non-existent. 
     Thus, in view of the above circumstances, it is an object of the present invention to provide a broadcasting receiver and a method for seeking broadcasting, which is capable of decreasing the time needed for the channel seeking operation. 
     In accordance with the embodiment of the invention, a broadcasting receiver suitable for receiving a broadcasting signal transmitted in a signal format is provided in which a carrier wave is allocated in a frequency channel to have a certain frequency offset and a certain signal intensity, which comprises: an information acquiring means for acquiring information related to the frequency channel being sought; and a station existence determining means for determining whether the frequency channel is in a state of station-existent or not based on information acquired by the information acquiring means; and wherein the information acquiring means acquires information concerning a receiving intensity of carrier wave and information concerning a frequency offset. 
     With such an arrangement, the broadcasting receiver is capable of acquiring necessary information for determining whether the receivable digital broadcasting is performed or not in advance of performing the decoding of the digital broadcasting signal. Therefore, the decoding process of the digital broadcasting signal may be performed only when it is likely that the digital broadcasting is performed in the frequency channel in seek. By operating such that above time-lengthy decoding process is not performed on the channel in which digital broadcasting is not performed, it is enabled to decrease the time needed for the channel seeking operation. Further, since the information for the receiving intensity and the frequency offset for the carrier wave is acquired, it is enabled to determine the existence of the subcarrier for the digital broadcasting signal from those relations, and to determine accurately the broadcasting signal in all-digital format as station-existent also. 
     In addition, the broadcasting receiver may comprise an analog determining means for determining whether the carrier wave of the analog broadcasting signal is included in the frequency channel or not, based on the information acquired by the information acquiring means. 
     With such an arrangement, it is enabled to determine the existence of the carrier wave for analog broadcasting signal, which is important information useful for determining whether transmission of the broadcasting signal in all-digital format is performed or not in the frequency channel. 
     Additionally, the broadcasting receiver may comprise a digital determining means for determining whether carrier wave of the digital broadcasting signal is included in the frequency channel or not, based on the information acquired by the information acquiring means. 
     With such an arrangement, it is enabled to determine whether the digital broadcasting is performed in the frequency channel or not without decoding the digital broadcasting signal, which is a time-lengthy process. 
     Further, the broadcasting receiver may comprise a difference calculating means for calculating difference between a maximum value and a minimum value of the frequency offset of the carrier wave included in the frequency channel based on the information of frequency offset acquired by the information acquiring means; and an all-digital determining means for determining whether the broadcasting signal in the all-digital format that is signal format including only the carrier wave of the digital broadcasting signal is transmitted in the frequency channel or not. In this case, the all-digital determining means may determine that the broadcasting signal in all-digital format is transmitted in the frequency channel, when the station existence determining means determines that the frequency channel is in the state of station-existent, the analog determining means determines that the frequency channel does not include the carrier wave of the analog broadcasting signal, and the difference calculated by the difference calculating means is larger than or equal to a certain value. Furthermore, the difference calculating means may perform calculation of the difference when the station existence determining means determines that the frequency channel is in the state of station-existent, and the analog determining means determines that the frequency channel does not include the carrier wave of the analog broadcasting signal. 
     With such an arrangement, it is enabled to distinguish between broadcasting in hybrid format where analog signal and digital signal co-exists and broadcasting in all-digital format. 
     Further, the broadcasting receiver may comprise a decoding means for decoding the digital broadcasting signal; and an all-digital ascertaining means for ascertaining that the broadcasting signal in the all-digital digital format is transmitted in the frequency channel, based on the result of the decoding process by the decoding means. In this case, in the channel seek, the decoding process may be performed by the decoding means only when the all-digital determining means determines that the broadcasting signal in the all-digital format is transmitted in the frequency channel. 
     The receiver arranged as such performs the decoding process of the digital signal, which obstruct the smooth channel seeking operation due to long time required for the processing, only in the frequency channel that was determined in advance that the transmission of the broadcasting signal in all-digital format, which requires decoding process in channel seek, is performed. Therefore, fluent channel seeking is made possible. Further, it does not output the disturbing digital noise made due to analog demodulation, in a case with all-digital format, and the channel seeking is performed in comfort. 
     In accordance with the embodiment of the invention, a method for performing channel seek for a frequency channel is provided, wherein a broadcasting signal in a signal format in which a carrier wave of an analog broadcasting signal and/or a digital broadcasting signal is allocated to have a certain frequency offset and a signal intensity is transmitted in the frequency channel, the method comprising: an information acquiring step for acquiring information related to the frequency channel being sought; and a station existence determining step for determining whether the frequency channel is in a state of station-existent or not based on the information acquired in the information acquiring step; and wherein, in the information acquiring step, information concerning a receiving intensity of carrier wave and information concerning a frequency offset are acquired. 
    
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
         FIG. 1  A block diagram showing an arrangement of an audio apparatus comprising an IBOC broadcasting receiver according to an embodiment of the invention. 
         FIG. 2  A flowchart describing channel seeking process performed in the audio apparatus according to the embodiment of the invention. 
         FIG. 3  A flowchart describing channel seeking process performed in the audio apparatus according to the embodiment of the invention. 
         FIG. 4  A flowchart describing channel seeking process performed in the audio apparatus according to the embodiment of the invention. 
         FIG. 5  A flowchart describing channel seeking process performed in the audio apparatus according to the embodiment of the invention. 
         FIG. 6  A flowchart describing channel seeking process performed in the audio apparatus according to the embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following, an IBOC broadcasting receiver according an embodiment of the invention will be described referring to the drawings. 
       FIG. 1  is a block diagram illustrating an arrangement of an audio apparatus  100  including an IBOC broadcasting receiver according to an embodiment of the present invention. The audio apparatus  100  is mounted in, for example, a mobile vehicle. The audio apparatus  100  complies with IBOC radio broadcasting, and is designed to receive and process broadcasting signal in IBOC signal format. 
     The audio apparatus  100  includes an antenna  1 , a tuner  2 , an IF (Intermediate Frequency) amplifier  6 , a separator SEP, an IF filter  7 , an A/D converter  8 , an DSP (Digital Signal Processor)  9 , an audio processing circuit  10 , a D/A converter  11 , a power amplifier  12 , a speaker  13 , a PLL (Phase Locked Loop) circuit  14 , a microcomputer  15 , an IDM (IBOC Digital Module)  16 , an optical receiver  17 , and a remote controller  18 . 
     The remote controller  18  is provided with operation keys for operating the audio apparatus  100 . When the user operates the remote controller  18 , a control pulse associated with the operation is output from the remote controller  18 . Such control pulse output is, for example, a signal that complies with the IrDA standard. After the optical receiver  17  receives the control pulse that the remote controller  18  outputted, then passes it to the microcomputer  15 . 
     The microcomputer  15  governs the general control of the overall audio apparatus  100 . It executes those control programs based on the control pulse received from the optical receiver  17 , and controls elements within the audio apparatus  100 . 
     In the following, a series of signal processing in the audio apparatus  100  will be described. The antenna  1  receives RF (Radio Frequency) signal for channels of the radio broadcast. RF signal received on the antenna  1  is input to the tuner  2 . 
     The tuner  2  performs the frequency conversion into an intermediate frequency suitable for signal processing of filtering, etc., by selecting the RF signal of the selected channel among the input RF signals with the control carried out by the microcomputer  15  with the PLL circuit  14 . The IF signal acquired by the frequency conversion of the RF signal is input to the IF amplifier  6 . The selected channel is determined according to, for example, the station selecting operation with the user operation. The information regarding the last selected channel (hereinafter referred to as “last channel”) is, for example, held in the internal memory or a flash ROM (not shown) of the microcomputer  15 . 
     The IF amplifier  6  amplifies the input IF signal and outputs to the separator SEP. The separator SEP separates the input IF signal into two signal components based on, for example, the frequency. One of the separated components is a signal component obtained by converting the analog carrier wave into the IF signal (hereinafter, it is referred to as, “analog IF signal”), and the other one is a signal component obtained by converting the sideband subcarrier into the IF signal (hereinafter referred to as “digital IF signal”) The separator SEP outputs the separated analog IF signal and the digital IF signal to the IF filter  7  and the A/D converter  8 , respectively. 
     If only the analog radio broadcasting is transmitted in the selecting channel, substantially only the analog IF signal is input to the separator SEP. Therefore, the digital IF signal will not be obtained even if the separation process is performed at the separator SEP. In contrast, if only the digital radio broadcasting is transmitted in the selecting channel, substantially only the digital IF signal is input to the separator SEP. Therefore, the analog IF signal will not be obtained even if the separation process is performed at the separator SEP. 
     The IF filter  7  performs the filtering process that removes the unneeded frequency component from the input analog IF signal, and outputs the processed analog IF signal to the A/D converter  8 . The A/D converter  8  is provided with different A/D conversion processing circuits individually for analog IF signal and for digital IF signal. Then, the input analog and digital IF signal is A/D converted by the corresponding A/D conversion processing circuit, and is output to the DSP  9 . It is noted that the gain of the IF amplifier  6  is adjusted with the feedback control based on the level of the IF signal input to the A/D converter  8 . 
     The DSP  9  comprises a separator that separates the input IF signal into two signal components (analog IF signal and digital IF signal), based on, for example, frequency. Further, the DSP  9  comprises a wave detecting circuit, a noise canceller and a weak electric field processing circuit for demodulating the separated analog IF signal. 
     The DSP  9  outputs the separated analog IF signal to the wave detecting circuit, and also, outputs the digital IF signal to the IDM  16 . 
     The analog IF signal is demodulated to the audio signal by the wave detecting circuit, and then removed the noise by the noise canceller. After removing the noise, processing according to the receiving condition of the selecting channel (e.g., mute, high cut, separation control) is performed onto the signal by the weak electric field processing circuit. Then, the DSP  9  outputs the signal that underwent these series of processes to the audio processing circuit  10  as the analog audio signal. 
     It is noted that the DSP  9  does not perform the separation process by the separator if the channel seeking process, which will be described later, is being performed. Therefore, the input IF signal undergoes the wave detecting process, the noise removing process and the process by the weak electric field processing circuit. By means of these series of processes, the quality information for the checking channel is acquired. The quality information includes information such as the receiving intensity of the carrier wave for the checking channel, the offset value from the center frequency of the channel (hereinafter referred to as “frequency offset”), information showing the multipath noise (hereinafter referred to as “MPN”), information showing the adjacent disturbance, which is noise due to the signal in the adjacent channel (hereinafter it is referred to as “USN”). The obtained quality information is passed onto the microcomputer  15 . 
     The IDM  16  is a decoder for digital broadcasting signal for use only for IBOC. The IDM  16  performs a well-known decoding process to the input digital IF signal and acquires audio signal. Then, the acquired audio signal is output to the audio processing circuit  10 . For the purpose of description, the audio signal that underwent the IDM  16  process and was output is described as, “digital audio signal”. 
     Subsequently, the audio processing circuit  10  performs a predetermined process onto the input audio signal and inputs it to the D/A converter after adjusting the volume. 
     The D/A converter  11  performs a digital-to-analog conversion to the input audio signal and outputs to the power amplifier  12 . The power amplifier  12  amplifies the audio signal and outputs to the speaker  13 . Thereby, the radio broadcast is output and played at the speaker  13 . It is noted that the audio processing circuit  10  is implemented with a blend circuit that smoothly switches between the input analog audio signal and digital audio signal and outputs either one of them. With the blend circuit, when the output signal is switched from analog audio signal to digital audio signal (or alternatively, from digital audio signal to analog audio signal), the sound output from the speaker  13  is coupled naturally so that the user does not sense the switch occurred. 
     In the following, the channel seeking process related to the audio apparatus  100  of the present embodiment is described.  FIGS. 2-6  indicate the flowcharts that describe the channel seeking process performed by the audio apparatus  100 . The channel seeking process, which is described in  FIGS. 2-6 , starts when the user performs tuning up (or tuning down) operation (For example, pressing down once the “Tuning up” or “Tuning down” button) while the audio apparatus  100  is selecting some channel. 
     When the channel seeking process of the present embodiment starts, the microcomputer  15  performs the channel seeking operation in the direction corresponding to the user operation (Up or Down direction) (Step  1 . Hereinafter, the term “step” is abbreviated as next is searched by raising (or lowering) the frequency band for which the seeking operation is done. 
     Subsequently, the microcomputer  15  initializes the parameters related to each channel (S 2 ). The parameters that are initialized include “Analog NG flag”, “Digital NG flag”, “maximum frequency offset” and “minimum frequency offset”. 
     “Analog NG flag” is the information that indicates whether it can receive the analog radio broadcasting or not. “Digital NG flag” is the information that indicates whether it can receive the digital radio broadcasting or not. Flag value “0” indicates that it is able to receive the broadcasting corresponding to the flag. Flag value “1” indicates that it is not able to receive the broadcasting corresponding to the flag. 
     “Maximum frequency offset” indicates the largest offset value among the frequency offsets that can be obtained by DSP  9 . “Minimum frequency offset” indicates the smallest offset value among the frequency offsets that can be obtained by DSP  9 . Frequency offset is the parameter that indicates the difference between the frequency of carrier wave having an amplitude which is larger than the prescribed reference and the central frequency of the channel. The microcomputer  15  sets each frequency offset to “0” in the S 2  process. 
     When the frequency band for which seeking operation is performed is the channel on which digital radio broadcasting is being done, multiple frequency offsets can be obtained by DSP  9 . In this case, these frequency offsets indicate the offset value for each subcarrier of the digital radio broadcasting. “Maximum frequency offset” becomes the offset value for the subcarrier that is farthest on the plus side (direction in which frequency is high) from the center of the frequency band for which seek is performed. “Minimum frequency offset” is the offset value of the subcarrier that is farthest on the minus side (direction in which frequency is low) from the center. 
     After the S 2  process, the microcomputer  15  sets the count value M of the internal counter to “3” (S 3 ). Further, count value N of a different internal counter is set to “5” (S 4 ). After these count values are set, the microcomputer  15  receives the quality information, which was obtained by the process corresponding to the frequency band for which seeking operation is performed, from DSP  9  and maintains it in the internal memory (S 5 ). Every time the quality information is obtained by the execution of the S 5  process, the microcomputer  15  stores the information in the internal memory. In other words, if the S 5  process is performed twice, acquired quality information by the first and second S 5  process is stored in the internal memory. Hereinafter, for the purpose of description, the quality information acquired by the S 5  process is referred to as “acquired quality information”. 
     After the S 5  process, the microcomputer  15  maintains the maximum value of the frequency offset (included in the acquired quality information) as “maximum frequency offset” and the minimum value as “minimum frequency offset” (S 6 ). When execution of the step S 6  is the second time or later, the corresponding value is already held in the “maximum frequency offset” and “minimum frequency offset”. In this case, the frequency offset that is newly obtained is compared with the frequency offset that is held. If the value that is newly obtained is the largest, the “maximum frequency offset” is updated and if it is the smallest, the “minimum frequency offset” is updated. 
     After the S 6  process, the microcomputer  15  determines whether the receiving intensity included in the acquired quality information is greater than or equal to the threshold value (hereinafter referred to as “threshold value for the analog receiving intensity”) corresponding to the receiving intensity of the analog radio broadcasting that is set in advance (S 7 ). If the receiving intensity is determined to be greater than or equal to the threshold value for the analog receiving intensity (S 7 : YES), the microcomputer  15  determines the receiving intensity to be high enough to receive the analog radio broadcasting and proceeds to the S 9  process. On the other hand, when the receiving intensity is determined to be smaller than the threshold value for the analog receiving intensity (S 7 : NO), the microcomputer  15  determines that the analog radio broadcasting cannot be received as the receiving intensity is low. In this case, the “analog NG flag” is set to “1” (S 8 ) and the process proceeds to S 9 . 
     In the S 9  process, the microcomputer  15  determines whether the receiving intensity included in the acquired quality information is greater than or equal to the threshold value (hereinafter referred to as “threshold value for the digital receiving intensity”) corresponding to the receiving intensity of the digital radio broadcasting that is set in advance. When the receiving intensity is determined to be greater than or equal to the threshold value for the digital receiving intensity (S 9 : YES), the microcomputer  15  determines the receiving intensity to be high enough to receive the digital radio broadcasting and proceeds to the S 11  process. On the other hand, when the receiving intensity is determined to be smaller than the threshold value for the digital receiving intensity (S 9 : NO), the microcomputer  15  determines that the digital radio broadcasting cannot be received as the receiving intensity is low. In this case, the “analog NG flag” is set to “1” (S 10 ) and the process proceeds to S 11 . 
     In the S 11  process, the microcomputer  15  refers to the “analog NG flag” and “digital NG flag”. When both of these flags are “1” (S 11 : YES), it is determined that neither the analog radio broadcasting nor the digital radio broadcasting can be received. In this case, the process returns to S 1  and process is performed for the frequency band for which seek is performed. On the other hand, if at least one of these flags is “0” (S 11 : NO), the microcomputer  15  determines that at least one radio broadcasting can be received and the process proceeds to S 12 . 
     In the S 12  process, the microcomputer  15  determines whether the frequency offset included in the acquired quality information lies within the range (hereinafter referred to as “range for the analog frequency offset”) that is set for the analog radio broadcasting frequency offset. When it is determined to lie within the range for the analog frequency offset (S 12 : YES); the microcomputer  15  determines that it is able to receive the analog radio broadcasting since the noise influence is low, and the process proceeds to S 14 . On the other hand, when the frequency offset is determined to be outside the range of analog frequency offset (S 12 : NO), the microcomputer  15  determines that is not possible to receive the analog radio broadcasting as the noise influence is more. It then proceeds to the S 14  process after setting the “analog NG flag” to “1” (S 13 ). 
     In the S 14  process, the microcomputer  15  determines whether the frequency offset included in the acquired quality information lies within the range (hereinafter referred to as “range for the digital frequency offset”) that is set for the digital radio broadcasting frequency offset. When it is determined to lie within the range for the digital frequency offset (S 14 : YES), the microcomputer  15  determines that is possible to receive the digital radio broadcasting since the noise influence is low. The process thereafter proceeds to S 16 . On the other hand, when the frequency offset is determined to be outside the range of digital frequency offset (S 14 : NO), the microcomputer  15  determines that is not possible to receive the digital radio broadcasting as the noise influence is more. It then proceeds to the S 16  process after setting the “digital NG flag” to “1” (S 15 ). 
     Similar to the S 11  process, in the S 16  process too, the microcomputer  15  refers to the “analog NG flag” and “digital NG flag”. When both of these flags are “1” (S 16 : YES), the microcomputer  15  determines that neither the analog radio broadcasting nor the digital radio broadcasting can be received. In this case, the process returns to S 1  and starts the process for the frequency band for the next seeking operation. On the other hand, if at least one of these flags is “0” (S 16 : NO), the microcomputer  15  determines that at least one radio broadcasting can be received and the process proceeds to S 17 . 
     In the S 17  process, the microcomputer  15  determines whether USN included in the acquired quality information is smaller than the threshold value (hereinafter referred to as “threshold value for the analog USN”) corresponding to the USN of the analog radio broadcasting that is set in advance. When the USN included in the acquired quality information is determined to be smaller than the threshold value for the analog USN (S 17 : YES), the microcomputer  15  determines that the analog radio broadcasting can be received as the influence of adjacent disturbance is low and the process proceeds to S 19 . On the other hand, when it is determined to be greater than or equal to the threshold value for the analog USN (S 17 : NO), the microcomputer  15  determines that the analog radio broadcasting cannot be received as the influence of adjacent disturbance is high and the process proceeds to S 19  after setting (S 18 ) the “analog NG flag” to “1”. 
     In the S 19  process, the microcomputer  15  determines whether USN included in the acquired quality information is smaller than the threshold value (hereinafter referred to as “threshold value for the digital USN”) corresponding to the USN of the digital radio broadcasting that is set in advance. When the USN included in the acquired quality information is determined to be smaller than the threshold value for the digital USN (S 19 : YES), the microcomputer  15  determines that the digital radio broadcasting can be received as the influence of adjacent disturbance is low and the process proceeds to S 19 . On the other hand, when it is determined to be greater than or equal to the threshold value for the digital USN (S 19 : NO), the microcomputer  15  determines that the digital radio broadcasting cannot be received as the influence of adjacent disturbance is high and the process proceeds to S 21  after setting the “digital NG flag” to “1” (S 20 ). 
     Similar to the S 11  process, in the S 21  process too, the microcomputer  15  refers to the “analog NG flag” and “digital NG flag”. When both of these flags are “1” (S 21 : YES), the microcomputer  15  determines that neither the analog radio broadcasting nor the digital radio broadcasting can be received. In this case, the process returns to S 1  and the process for the frequency band for the next seeking operation is performed. On the other hand, if at least one of these flags is “0” (S 21 : NO), the microcomputer  15  determines that at least one radio broadcasting can be received and the process proceeds to S 22 . 
     In the S 22  process, the microcomputer  15  determines whether MPN included in the acquired quality information is smaller than the threshold value (hereinafter referred to as “threshold value for the analog MPN”) corresponding to the MPN of the analog radio broadcasting that is set in advance. When the MPN included in the acquired quality information is determined to be smaller than the threshold value for the analog MPN (S 22 : YES), the microcomputer  15  determines that the analog radio broadcasting can be received as the influence of multipath noise is low and the process then proceeds to S 24 . On the other hand, when it is determined to be greater than or equal to the threshold value for the analog MPN (S 22 : NO), the microcomputer  15  determines that the analog radio broadcasting cannot be received as the influence of multipath noise is high and the process then proceeds to S 24  after setting the “analog NG flag” to “1” (S 23 ). 
     In the S 24  process, the microcomputer  15  determines whether MPN included in the acquired quality information is smaller than the threshold value (hereinafter referred to as “threshold value for the digital MPN”) corresponding to the MPN of the digital radio broadcasting that is set in advance. When the MPN included in the acquired quality information is determined to be smaller than the threshold value for the digital MPN (S 24 : YES), the microcomputer  15  determines that the digital radio broadcasting can be received as the influence of multipath noise is low and the process then proceeds to S 26 . On the other hand, when it is determined to be greater than or equal to the threshold value for the digital MPN (S 24 : NO), the microcomputer  15  determines that the digital radio broadcasting cannot be received as the influence of multipath noise is high and the process then proceeds to S 26  after setting the “digital NG flag” to “1” (S 25 ). 
     Similar to the S 11  process, in the S 26  process too, the microcomputer  15  refers to the “analog NG flag” and “digital NG flag”. When both of these flags are “1” (S 26 : YES), the microcomputer  15  determines that neither the analog radio broadcasting nor the digital radio broadcasting can be received. In this case, the process returns to S 1  and the process for the frequency band for the next seeking operation is performed. On the other hand, if at least one of these flags is “0” (S 26 : NO), the microcomputer  15  determines that at least one radio broadcasting can be received and the process proceeds to S 27 . 
     In the S 27  process, the microcomputer  15  decrements the count value N by 1 and then determines whether the count value N is “0” (S 28 ). If the count value N is determined to be “0” (S 28 : YES), the microcomputer  15  determines that the Steps  5 - 27  processes has been repeated N times and proceeds to the S 29  process. On the other hand, if the count value N is not “0” (S 28 : NO), the microcomputer  15  determines that the Steps  5 - 27  processes has not been performed N times and returns to the S 5  process. 
     In the S 29  process, the microcomputer  15  calculates the average value of receiving intensity for the N batches stored in the internal memory. After that, the microcomputer  15  determines whether the average value (hereinafter referred to as the “average receiving intensity”) of the calculated receiving intensity is greater than or equal to the threshold value (hereinafter referred to as the “threshold value for analog average receiving intensity”) corresponding to the average receiving intensity of the analog radio broadcasting set in advance. If the value is greater than or equal to the threshold value for analog average receiving intensity (S 29 : YES), the microcomputer  15  determines that the analog radio broadcasting can be received stably as the receiving intensity is continuously high. The process thereafter proceeds to S 31 . On the other hand, if the value is smaller than the threshold value for analog average receiving intensity (S 29 : NO), the microcomputer  15  determines that the analog radio broadcasting cannot be received as the receiving intensity is unstable. In this case, the “analog NG flag” is set to “1” (S 30 ) and the process proceeds to S 31 . 
     In the S 31  process, the microcomputer  15  determines whether the average receiving intensity is greater than or equal to the threshold value (hereinafter referred to as the “threshold value for digital average receiving intensity”) corresponding to the average receiving intensity of the digital radio broadcasting set in advance. If the intensity is greater than or equal to the threshold value for digital average receiving intensity (S 31 : YES), the microcomputer  15  determines that the digital radio broadcasting can be received stably as the receiving intensity is continuously high. The process thereafter proceeds to S 33 . On the other hand, if the intensity is smaller than the threshold value for digital average receiving intensity (S 31 : NO), the microcomputer  15  determines that the digital radio broadcasting cannot be received as the receiving intensity is unstable. In this case, the “digital NG flag” is set to “1” (S 32 ) and the process proceeds to S 33 . 
     Similar to the S 11  process, in the S 33  process too, the microcomputer  15  refers to the “analog NG flag” and “digital NG flag”. When both of these flags are “1” (S 33 : YES), the microcomputer  15  determines that neither the analog radio broadcasting nor the digital radio broadcasting can be received. In this case, the process returns to S 1  and the process for the frequency band for the next seeking operation is performed. On the other hand, if at least one of these flags is “0” (S 33 : NO), the microcomputer  15  determines that at least one radio broadcasting can be received and the process proceeds to S 34 . 
     In the S 34  process, the microcomputer  15  calculates the average value of frequency offset for the N batches stored in the internal memory. After that, the microcomputer  15  determines whether the average value (hereinafter referred to as the “average frequency offset”) of the calculated frequency offset is included in the range (hereinafter referred to as the “range for analog average frequency offset”) set for the average frequency offset of the analog radio broadcasting. If the average frequency offset is within the range for analog average frequency offset (S 34 : YES), the microcomputer  15  determines that the analog radio broadcasting can be received stably as the noise influence is continuously low. The process thereafter proceeds to S 36 . On the other hand, if the average frequency offset is outside the range for analog average frequency offset (S 34 : NO), the microcomputer  15  determines that the analog radio broadcasting cannot be received as the noise influence is high and the reception status is unstable. In this case, the “analog NG flag” is set to “1” (S 35 ) and the process proceeds to S 36 . 
     In the S 36  process, the microcomputer  15  determines whether the average frequency offset is included in the range (hereinafter referred to as the “range for digital average frequency offset”) set for the average frequency offset of the digital radio broadcasting. If the average frequency offset is determined to be within the range for digital average frequency offset (S 36 : YES), the microcomputer  15  determines that the digital radio broadcasting can be received stably as the noise influence is continuously low. The process thereafter proceeds to S 38 . On the other hand, if the average frequency offset is determined to be outside the range for digital average frequency offset (S 36 : NO), the microcomputer  15  determines that the digital radio broadcasting cannot be received as the noise influence is high and the reception status is unstable. In this case, the “digital NG flag” is set to “1” (S 37 ) and the process proceeds to S 38 . 
     Similar to the S 11  process, in the S 38  process too, the microcomputer  15  refers to the “analog NG flag” and “digital NG flag”. When both of these flags are “1” (S 38 : YES), the microcomputer  15  determines that neither the analog radio broadcasting nor the digital radio broadcasting can be received. In this case, the process returns to S 1  and the process for the frequency band for the next seeking operation is performed. On the other hand, if at least one of these flags is “0” (S 38 : NO), the microcomputer  15  determines that at least one radio broadcasting can be received and the process proceeds to S 39 . 
     In the S 39  process, the microcomputer  15  calculates the average value of USN for the N batches stored in the internal memory. After that, the microcomputer  15  determines whether the average value (hereinafter referred to as the “average USN”) of the calculated USN is less than the threshold value (hereinafter referred to as the “threshold value for the analog average USN”) corresponding to the average USN of the analog radio broadcasting set in advance. If the average USN is less than the threshold value for the analog average USN (S 39 : YES), the microcomputer  15  determines that the analog radio broadcasting can be received as the influence of adjacent disturbance is continuously low. The process thereafter proceeds to S 41 . On the other hand, if the average USN is more than the threshold value for the analog average USN (S 39 : NO), the microcomputer  15  determines that the analog radio broadcasting cannot be received as the influence of adjacent disturbance is high and the reception status is unstable. In this case, the “analog NG flag” is set to “1” (S 40 ) and the process proceeds to S 41 . 
     In the S 41  process, the microcomputer  15  determines whether the average USN is less than the threshold value (hereinafter referred to as the “threshold value for the digital average USN”) corresponding to the average USN of the digital radio broadcasting set in advance. If the average USN is less than the threshold value for the digital average USN (S 41 : YES), the microcomputer  15  determines that the digital radio broadcasting can be received as the influence of adjacent disturbance is continuously low. The process thereafter proceeds to S 43 . On the other hand, if the average USN is more than the threshold value for the digital average USN (S 41 : NO), the microcomputer  15  determines that the digital radio broadcasting cannot be received as the influence of adjacent disturbance is high and the reception status is unstable. In this case, the “digital NG flag” is set to “1” (S 42 ) and the process proceeds to S 43 . 
     Similar to the S 11  process, in the S 43  process too, the microcomputer  15  refers to the “analog NG flag” and “digital NG flag”. When both of these flags are “1” (S 43 : YES), the microcomputer  15  determines that neither the analog radio broadcasting nor the digital radio broadcasting can be received. In this case, the process returns to S 1  and the process for the frequency band for the next seeking operation is performed. On the other hand, if at least one of these flags is “0” (S 43 : NO), the microcomputer  15  determines that at least one radio broadcasting can be received and the process proceeds to S 44 . 
     In the S 44  process, the microcomputer  15  calculates the average value of MPN for the N batches stored in the internal memory. After that, the microcomputer  15  determines whether the average value (hereinafter referred to as the “average MPN”) of the calculated MPN is less than the threshold value (hereinafter referred to as the “threshold value for the analog average MPN”) corresponding to the average MPN of the analog radio broadcasting set in advance. If the average MPN is less than the threshold value for the analog average MPN (S 44 : YES), the microcomputer  15  determines that the analog radio broadcasting can be received as the influence of multipath noise is continuously low. The process thereafter proceeds to S 46 . On the other hand, if the average MPN is more than the threshold value for the analog average MPN (S 44 : NO), the microcomputer  15  determines that the analog radio broadcasting cannot be received as the influence of multipath noise is high and the reception status is unstable. In this case, the “analog NG flag” is set to “1” (S 45 ) and the process proceeds to S 46 . 
     In the S 46  process, the microcomputer  15  determines whether the average MPN is less than the threshold value (hereinafter referred to as the “threshold value for the digital average MPN”) corresponding to the average MPN of the digital radio broadcasting set in advance. If the average MPN is less than the threshold value for the digital average MPN (S 46 : YES), the microcomputer  15  determines that the digital radio broadcasting can be received as the influence of multipath noise is continuously low. The process thereafter proceeds to S 48 . On the other hand, if the average MPN is more than the threshold value for the digital average MPN (S 46 : NO), the microcomputer  15  determines that the digital radio broadcasting cannot be received as the influence of multipath noise is high and the reception status is unstable. In this case, the “digital NG flag” is set to “1” (S 47 ) and the process proceeds to S 48 . 
     Similar to the S 11  process, in the S 48  process too, the microcomputer  15  refers to the “analog NG flag” and “digital NG flag”. When both of these flags are “1” (S 48 : YES), the microcomputer  15  determines that neither the analog radio broadcasting nor the digital radio broadcasting can be received. In this case, the process returns to S 1  and the process for the frequency band for the next seeking operation is performed. On the other hand, if at least one of these flags is “0” (S 48 : NO), the microcomputer  15  determines that at least one radio broadcasting can be received and the process proceeds to S 50 . 
     In the S 50  process, the microcomputer  15  decrements the count value M by 1 and then determines whether the count value M is “0” (S 51 ). If the count value M is “0” (S 51 : YES), the microcomputer  15  determines that the frequency band for which seeking operation is performed is station-existent as a result of repeating the Steps  4 - 50  processes M times. The process thereafter proceeds to S 52 . On the other hand, when the count value M is not “0” (S 51 : NO), the microcomputer  15  determines that the Steps  4 - 50  processes are not performed M times. The acquired quality information as well as each average value (average receiving intensity, average frequency offset, average USN and average MPN) of the quality information stored in the internal memory is deleted (S 49 ) and the process returns to S 4 . 
     In the S 52  process, the microcomputer  15  determines whether the “analog NG flag” is “0”. When the “analog NG flag” is “0” (S 52 : YES), the microcomputer  15  determines that the frequency band for which seeking operation is performed is the analog radio broadcasting or hybrid broadcasting (broadcasting that includes analog as well as digital radio broadcasting). In addition to this, it is ascertained that the analog radio broadcasting is included in the frequency band. After that, the channel seeking operation is stopped (i.e., this flow chart is ended) with the frequency band selected. Thereby, the analog radio broadcasting of the selected channel is played at the speaker  13 . It is also possible to switch to the digital radio broadcasting of the selected channel by performing the prescribed user operation. 
     In the S 52  process, the microcomputer  15  calculates the difference A between “maximum frequency offset” and “minimum frequency offset” when it is determined (S 52 : NO) that “analog NG flag” is not “0” (i.e., “digital NG flag” is “0”). After that, the microcomputer  15  also determines (S 53 ) whether the calculated difference A is greater than or equal to the prescribed threshold value B. 
     In the S 53  process, when the difference A is determined to be less than the threshold value B (S 53 : NO), the microcomputer  15  determines that the frequency band for which seeking operation is performed includes an extremely weak analog radio broadcasting or does not include any other type of radio broadcasting. The process then returns to S 1  and the process for the frequency band for the next seeking operation is performed. 
     In the S 53  process, when the microcomputer  15  determines (S 53 : YES) that the difference A is greater than or equal to the threshold value B, it is determined that the frequency band for which seeking operation is performed is most probably a channel that includes only the digital radio broadcasting. Then, the decoding process is performed by controlling the IDM  16 . If IBOC signal (i.e., identification information which indicates that it is a digital radio broadcasting) is obtained (S 54 : YES) by this decoding process, the microcomputer  15  ascertains that the frequency band for which seeking operation is performed is the channel that includes only the digital radio broadcasting. The channel seeking operation is stopped (i.e., this flowchart is ended) with the frequency band selected. 
     Thereby, the digital radio broadcasting of the selected channel is played at the speaker  13 . When IOBC signal is not obtained (S 54 : NO) by the above-mentioned decoding process, the microcomputer  15  determines that the frequency band for which seeking operation is performed does not include any kind of radio broadcasting. In this case, the process returns to S 1  and the process for the frequency band for the next seeking operation is performed. 
     In other words, depending on the audio apparatus  100  of the present embodiment, the determination process is performed by using the quality information of the frequency band for which the seeking operation is performed. The decoding process by the IDM  16  is performed only for the broadcasting that is determined to be most probably a digital radio broadcasting. Thereby, the channel seeking operation can be performed with a high accuracy and the decoding process performed by means of IDM  16  is not performed in vain. As a result, it is possible to decrease the time required for the channel seeking operation. In addition, by obtaining the frequency offset (“maximum frequency offset” and “minimum frequency offset”) and using it in the prescribed determination process, it is also possible to determine whether the frequency band that is determined to be station-existent is a channel that includes only the digital radio broadcasting or is noise, etc. 
     The embodiments of the present invention are as described in the above. The present invention is not limited only to these embodiments but can be changed in various ranges. For example, although the audio apparatus  100  comprising the IBOC broadcasting receiver of the present embodiment is equipped in a vehicle, it may be a portable appliance that a person can carry in other embodiments.