JP2013223055A - Digital broadcast receiving apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a "digital broadcast receiving apparatus" capable of controlling a dynamic range by utilizing data, relating to volume, contained in received audio signals.SOLUTION: A receiving apparatus of the present invention comprises a volume control section 25 which controls the volume in outputting audio data on the basis of a DRC value added to a frame of a digital audio signal, and a controller 40 which controls the volume control section 25. The controller 40 includes inference means which infers the volume of received audio data, setting means which sets an allowable range of the DRC value on the basis of the inferred volume, determination means which determines whether the DRC value is included within the allowable range, and correction means which corrects the DRC value when it is determined that the DRC value is out of the allowable range. The controller 40 controls the volume in accordance with a DRC value when the DRC value is settled within the allowable range, and controls the volume in accordance with a corrected DRC value when the DRC value is out of the allowable range.

Description

  The present invention relates to a receiver for digital broadcasting, and more particularly to a receiver for receiving a digital audio broadcast (hereinafter referred to as DAB) that has been put to practical use in Europe and the like.

  DAB has a function for a broadcast station to control the gain of an audio signal line in a receiver, which is called DRC (dynamic range control) (Patent Document 1). FIG. 1 shows the structure of data transmitted by a broadcast station, and one frame includes a header, audio data, SCF, SCF-CRC, F-PAD, and the like. Audio data is compressed by MPEG1 / 2 audio layer 2, and SCF is a scale factor at the time of data compression. SCF-CRC is an SCF error check code, and DRC data is included in 6 bits in a 2-byte area of F-PAD. The frame length of the MPEG1 / 2 audio layer r2 used in DAB is 24 ms. In DAB, a unique DRC value is added (as PAD data) to this frame and transmitted. The DRC data and the gain of the audio signal line have a relationship as shown in FIG. 2, and if the DRC data increases, the volume of the receiver is controlled to increase compulsorily (Patent Document 1). ).

  For F-PAD area and DRC data, there is no error check or error correction mechanism. Therefore, even if the reception environment deteriorates due to multipath or strong fading, and errors occur in the received DRC data, An error cannot be detected or corrected, and the volume may suddenly increase due to an error in DRC data. Therefore, in Patent Document 1, when it is considered that the latest DRC data has been normally received and the gain change width between the immediately preceding DRC data and the latest DRC data does not exceed the allowable value, the latest DRC data is obtained. When the DRC function is executed using the gain indicated by the error check code and the error check code SCF-CRC indicates an error, the DRC data is considered to have a high possibility of an error, and the gain of the audio signal line is determined. I am trying not to change it.

JP-A-11-330998

  As described above, when receiving a radio broadcast by DAB, if the DRC function is set to ON on the receiver side, the volume on the receiver side is automatically corrected by the DRC data. However, since the DRC data does not have an error check function, there is a problem that a sudden volume change is likely to occur when an error occurs in the DRC data particularly in a weak electric field.

  With respect to this problem, Patent Document 1 considers that there is an error in the DRC data when the error is detected by the SCF-CRC, and turns off the DRC function, and at the normal time when no error is detected by the SCF-CRC, If the change width of the DRC data does not exceed the allowable value, the gain based on the DRC data is executed. However, since the method of Patent Document 1 does not pay attention to the characteristics of the compressed audio signal, a malfunction is likely to occur in a normal time when no error is detected by SCF-CRC, and there is still a problem in terms of accuracy. For example, as shown in FIG. 3, when the audio signal having a high volume and a low volume is alternately transmitted from the broadcast station, the DRC data becomes small when the volume is high, and the DRC data becomes large when the volume is low. For this reason, when the volume changes, the amount of change D of the DRC data increases, and the method of Patent Document 1 is highly likely to limit the DRC function by mistake.

  In order to prevent malfunction due to the DRC function, it is possible to turn off the DRC function on the receiver side. However, in the reception environment of a moving body such as an automobile, it is difficult to hear the sound due to noise during traveling. It is desirable to compress the dynamic range using the function and increase the volume of the output audio

  An object of the present invention is to solve such a conventional problem, and to provide a digital broadcast receiving apparatus capable of controlling a dynamic range using data relating to a volume included in a received audio signal. To do.

  A receiving apparatus according to the present invention receives audio data and a compression-coded digital audio signal including control data for controlling the volume of the audio data, and receives the digital audio signal. Means, volume control means for controlling the volume when the audio data is output based on the control data contained in the received digital audio signal, and a digital audio signal whose volume is controlled by the volume control means Sound output means for outputting sound based on the sound volume control means, the sound volume control means for estimating the sound volume of the received audio data, and a setting for setting an allowable range of control data based on the estimated sound volume And a determination for determining whether or not the control data is included in the allowable range And a correction means for correcting the control data when the control data is determined to be outside the allowable range, and the volume control means determines that the control data is within the allowable range. When it is determined, the volume is controlled by the control data, and when it is determined that the control data is outside the allowable range, the volume is controlled by the corrected control data.

  Preferably, the receiving apparatus further includes error detection means for detecting an error of the digital audio signal based on an error detection code included in the received digital audio signal, and the volume control means has no error detected by the detection means. In this case, the volume is controlled using the control data, and when an error is detected by the detection means, the volume control by the control data is stopped. Preferably, the estimation means estimates the volume of the audio data based on the sum of data related to the amplitude of each frequency band of the received audio data. The estimating means may estimate the volume of the audio data based on data relating to the maximum amplitude among the data relating to the amplitude of each frequency band of the received audio data. Further, the estimation means may estimate the volume of the audio data based on an average of data related to the amplitude of each frequency band of the received audio data. Further, the estimation means may estimate the volume of the audio data based on the sum of the data related to the amplitude of a certain level or more among the data related to the amplitude of each frequency band of the received audio data. Preferably, the data relating to the amplitude is a scale factor included in the compressed digital audio signal. Preferably, the correction means corrects the control data to the lower limit value when the control data is smaller than the lower limit value of the allowable range, and when the control data is larger than the upper limit value of the allowable range, The control data is corrected to the upper limit value. Preferably, the receiving device further includes reception state determination means for determining whether or not the reception state is good based on data relating to the electric field strength of the received digital audio signal, and the volume control means detects an error by the detection means. And when the reception state is determined to be good by the reception state determination unit, the volume is controlled using the control data, and an error is detected by the detection unit, or the reception state determination unit When it is determined that the reception state is not good, the control of the sound volume by the control data is stopped. Preferably, the control data is DRC data.

  According to the present invention, the volume of the received audio data is estimated, and it is determined whether or not the control data is acceptable based on the estimation result, thereby preventing malfunction during volume control by the control data, Volume control can be performed with high accuracy.

It is a figure which shows the data structure of the flame | frame of the audio signal transmitted by DAB disclosed by a prior art. It is a figure which shows the relationship between DRC data and a gain. It is a figure explaining the subject of the DAB receiver disclosed by a prior art. It is a figure which shows the structure of the flame | frame of the compression-coded digital audio signal. It is a figure which shows the structural example of the DAB receiver which concerns on the Example of this invention. It is a figure which shows the volume control flow of the DAB receiver which concerns on 1st Example of this invention. It is a flow explaining the sound volume estimation method which concerns on the Example of this invention. It is a figure explaining the DRC function which concerns on the Example of this invention. It is a figure which shows the volume control flow of the DAB receiver which concerns on 2nd Example of this invention.

  Next, embodiments of the present invention will be described with reference to the drawings. A preferred embodiment of the present invention exemplifies a digital broadcast receiving apparatus mounted on a car as a moving body. In a preferred embodiment, the digital broadcast receiving apparatus is applied to DAB standardized in Europe and the like. However, the present invention can also be applied to reception of digital audio signals according to other standards.

  DAB employs MPEG1 / 2 audio layer 2 as a data compression method for audio signals. In MPEG1 / 2 audio layer 2, audio to be reproduced is divided into 32 frequency bands (subbands). Looking at the left and right channels, there are 64 frequency bands. Then, the divided audio signal for each subband is quantized. At this time, it is compressed more efficiently by using a “viewing psychology model” (a characteristic that a person has a large sound at a certain frequency and does not notice a small sound at a frequency close to that). For these processes, FFT (Fourier transform) is used. The compressed audio signal is transmitted by OFDM modulation. Therefore, the frame structure of the digital audio signal in DAB is substantially the same as that of MPEG1 / 2 audio layer 2. FIG. 4 shows a schematic configuration of the frame. The names here are given for convenience of explanation, and the actual configuration is the same as that of the frame shown in FIG. One frame includes a header part, a body part, and an additional data part, and its transmission time is 24 ms.

  The allocation unit includes information on whether or not audio data actually exists in the frequency band for each subband generated by dividing the whole into 32 parts. Since the compression rate can be improved by omitting non-existing subband waveform data and the like, such information is necessary. The SCF section is a ScaleFactor (scale factor), and stores data of amplitude values (volume levels) of the existing subbands. The CRC part stores data of the error detection function performed for the header part. Therefore, regarding the header portion, it is possible to detect the presence or absence of an error by processing using a CRC value. The body portion stores data indicating the waveform (amplitude) of each normalized subband. Therefore, the SCF part is also a magnification of the normalized waveform (amplitude) in the body part. Hereinafter, for convenience, the data stored in the SCF section is referred to as an SCF value. The additional data portion stores a DRC value added by the broadcasting station. However, the additional data portion is not provided with an error detection function (CRC portion).

  Next, FIG. 5 shows a configuration example of the DAB receiving apparatus in the present embodiment. In the DAB receiver 10 of the present embodiment, the front end 14 receives a broadcast wave RF signal from the antenna 12 and selects a frequency signal of a desired station from the received RF signal, and a frequency signal from a local transmitter. And an RF signal to generate an intermediate frequency (IF) signal, a DC meter for detecting the intermediate frequency signal, and an S meter circuit for extracting a received electric field strength signal (S meter signal). The intermediate frequency signal is converted into a digital signal by the A / D converter 16, and this signal is subjected to various signal processing in the signal processing unit 20.

  The signal processing unit 20 is configured using, for example, a DSP (Digital Signal Processor). The digital signal output from the A / D converter 16 is demodulated by the quadrature demodulator 21 to demodulate the signal of the quadrature component of the digital signal. The error correction unit 23 performs error correction using a Viterbi decoder or the like. The decoder 24 decompresses the compressed audio data, multiplies the SCF value (data related to the amplitude) of the SCF part of each subband and the normalized audio waveform data of the body part, and adds them to add digital audio. Synthesize the data. The volume or gain of the digital audio data is controlled by the volume controller 25 based on the DRC value. In addition to the above processing, the signal processing unit 20 also performs synchronization control of each unit. Such an operation of the signal processing unit 20 may be performed using a program stored in advance in the memory. Next, the digital audio signal output from the signal processing unit 20 is converted into an analog signal by the D / A converter 30 and is output as sound through the amplifier 32 and the speaker 34.

  The controller 40 controls the front end 14, the signal processing unit 20, and the like. In a preferred embodiment, the controller 40 controls each unit by executing a program stored in the memory. The controller 40 causes the front end 14 to select a desired broadcast station in response to an instruction from the user via the input unit 42, or outputs a sound via the volume control unit 25 based on the DRC value extracted from the decoder 24. Control the volume of the. In addition, the controller 40 displays the reception frequency and the broadcasting station name on the display unit 44 and stores necessary data in the memory 46.

  Next, the sound volume control operation based on the DRC value in the DAB receiver of this embodiment will be described. In a moving body such as a vehicle, noise may occur during traveling, and the output sound may be difficult to hear. One method for solving this problem is volume control using a DRC value added to an audio signal from a broadcasting station. As the DRC value increases, the volume or sound pressure (dB) gain is controlled to increase, and the dynamic range is compressed. In the preferred embodiment, the decoder 24 provides the controller 40 with the information HD regarding the header portion of the decoded audio signal and the DRC value contained in the additional data portion. The controller 40 detects whether or not there is an error in the header portion of the transmission frame by determining the CRC value. If an error is detected, the controller 40 turns off the DRC function, and if no error is detected, the DRC function. A control signal CNT for turning on the sound is output to the volume control unit 25. Further, when the DRC function is turned on, the DRC value or the corrected DRC value is output to the volume control unit 25. When the DRC function is turned off, the volume control unit 25 outputs the decoded audio signal as it is without controlling the volume based on the DRC value. When the DRC function is turned on, the volume control unit 25 adjusts the gain based on the DRC value. Is output. In another preferred embodiment, the controller 40 receives the electric field strength signal S1 from the front end 14 and the signal S2 related to error correction from the error correction unit 23, and the DRC function by the volume control unit 25 based on these signals S1 and S2. Can be controlled on / off.

  A flow of the volume control operation by the controller 40 is shown in FIG. First, a frame of an audio signal transmitted from a broadcasting station is received by the signal processing unit 20 (S101), and the controller 40 detects whether or not there is an error in the header part by the CRC value included in the frame. (S102). When an error is detected by the controller 40 (S103), the controller 40 determines that there is a high possibility that an error has occurred in the DRC value, and outputs a control signal CNT that turns off the DRC function (S104). ). This prevents a sudden explosion from the speaker 34 in advance. When turning off the DRC function, the audio signal may be muted in addition to stopping the volume control based on the DRC value.

  On the other hand, when no error is detected (S103), the controller 40 refers to the SCF value of each subband (S105) and estimates the volume of the frame based on these (S106). The volume estimation will be described in detail later. Next, an allowable range W of the DRC value assumed from the estimated sound volume is set (S107), and then the DRC value of the received frame is compared with the allowable range W (S108), and the DRC value is within the allowable range. It is determined whether it is within W (S109). If the DRC value is within the allowable range W, the received DRC value is regarded as correct, and the received DRC value is used as it is to control the volume (S110). On the other hand, if the DRC value is outside the allowable range W, it is assumed that the DRC value may be incorrect, the DRC value is corrected to the upper limit value or the lower limit value of the allowable range, and the corrected DRC value is The volume is controlled by using (S111).

  Next, the estimation of the volume of audio data in a frame will be described with reference to the flow of FIG. The controller 40 checks the allocation part in the header part expanded by the decoder 24, and identifies the subband in which the audio data exists (S201). Next, the controller 40 reads the SCF value of the subband identified as having data (S202), and estimates the volume of the frame by adding the read SCF values (S203). If audio data exists in all subbands, the SCF values of 32 subbands are added together.

  Next, the controller 40 calculates the allowable range W of the DRC value assumed from the estimated volume, and sets this (S204). In a preferred example, the controller 40 holds a table that defines the relationship between the estimated volume and the allowable range W, and sets the allowable range W with reference to the table. In another preferred example, the controller 40 may calculate the upper limit value and the lower limit value of the allowable range W from the sound volume estimated according to a predetermined mathematical formula.

  FIG. 8 is a graph for explaining volume control by the DRC function of this embodiment. When the DRC function is on, the audio data of the received frame is controlled so that its volume or gain increases according to the DRC value. As shown in the figure, a broadcasting station typically adds a DRC value so that the DRC value is small when the volume level is large and the DRC value is large when the volume level is small. This is because if the volume of the output sound is reduced, the volume is equal to or lower than the noise level, making it difficult to hear the sound.

  In this embodiment, when the DRC function is turned on, the allowable range W of the DRC value is calculated from the estimated volume, and if the received DRC value falls within the allowable range W, the volume control is performed using the DRC value as it is. Do. In the illustrated example, the allowable range W is set to be inversely proportional to the volume level, that is, when the estimated volume level is high, the allowable range W is small, and when the volume level is low, the allowable range W is large. . If the DRC value is within the allowable range W, the controller 40 outputs the received DRC value to the volume control unit 25 as it is.

  On the other hand, if the received DRC value does not fall within the allowable range W and the DRC value is smaller than the lower limit value of the allowable range W, the controller 40 corrects the received DRC value to the lower limit value, and If the DRC value is larger than the upper limit value, the received DRC value is corrected to the upper limit value, and the corrected DRC value is output to the volume control unit 25. In this way, when deviating from the allowable range W, imposing a certain limit on the DRC value prevents malfunction when the DRC function is on. The correction of the DRC value is not necessarily the upper limit value or the lower limit value, and may be any value as long as it falls within the allowable range W. Note that the sound volume estimation according to the present embodiment may be calculated from either the voltage value or the power value of the sound volume value (data regarding amplitude) stored in the SFC unit for each subband.

  Next, another method for estimating the volume of this embodiment will be described. In the method shown in FIG. 7, an example in which all the SCF values of the subbands are added is shown, but the sound volume estimation method is not necessarily limited to this. As a first modification, the volume of audio data can be estimated from the maximum SFC value in each subband. As a second modification, the SCF values of the subbands may be added together, then an average value may be calculated, and the volume of audio data may be estimated from the average value. As a third modified example, the sound volume may be estimated by extracting data related to an amplitude of a certain level or more and adding the extracted data.

  Next, a second embodiment of the present invention will be described. The audio compression encoding method used in DAB is based on MPEG1 / 2 audio layer 2, and a CRC value is added to the header portion of the compressed audio frame (packet). However, there is an algorithmic defect in the determination by CRC, which is very low probability for the case where there is an error in the “data part” and there is an error in the “transmitted CRC value”, but there is an error. If the CRC value obtained by calculation from the data part of this data coincides with the “transmitted CRC value” (also with an error), it is determined that there is no error, and there is a possibility of “missing an error”.

  In the flow shown in FIG. 6 described above, CRC determination of the MPEG header portion is performed, and if the result is a match, it is determined that the transmitted volume (sound pressure) data is correct, and the DRC value estimation process is performed. If the CRC judgment does not match, it is determined that there is an error in the transmitted data, and the estimation process is not performed. However, as described above, the CRC determination itself may occasionally be mistaken. In such a case, the prevention of malfunction of DRC, which is the original purpose of the present invention, is compromised. Therefore, the second embodiment adds reception state determination based on the parameter of electric field strength to the algorithm for preventing malfunction of the DRC function.

  As a rule of thumb, an error in CRC determination occurs most often when reception is performed in a weak electric field and the data often contains errors. One of the countermeasures is to incorporate into the judgment algorithm whether or not a weak electric field is received. FIG. 9 shows a volume control flow of the DAB receiver of the second embodiment. In the second embodiment, no error is detected by the error check code of the CRC part of the header part (S302), and the reception state determination by the parameter depending on the electric field strength at the time of frame reception is good (S303). If both conditions are not satisfied, the DRC function for the frame is turned off. If the DRC function is turned off, the volume is expected to decrease.

  In a preferred embodiment, the determination as to whether the reception state is good is made by comparing a parameter that depends on the electric field strength with a threshold value, and when the parameter is equal to or greater than (or less than) the threshold value, Is determined to be good. Here, the “parameters depending on the electric field strength” are RSSI (received electric field strength), the number of error corrections of a Vitarbi decoder of an FEC (error corrector) mounted in the case of DAB, and the like. The former is supplied to the controller 40 as a signal S1 from the front end 14 and the latter as a signal S2 from the decoder 24. For example, if the received electric field strength is greater than or equal to the threshold value, the controller 40 determines that the reception state of the frame is good. If the number of error corrections is equal to or less than the threshold value, the controller 40 determines that the reception state of the frame is good. Except for steps S302 and S303, the flow is the same as that shown in FIG.

  Further, there is DAB + / T-DMB or the like as a broadcasting standard that has the same flow as DAB, and the DAB + / T-DMB audio compression coding system is HE-AAC-V2 (AAC +). While DAB has only a Viterbi decoder in FEC, RS (Reed Solomon) is also installed in addition to the Viterbi decoder. The main difference between the Viterbi decoder and Reed-Solomon is that the Viterbi decoder cannot detect whether there are any errors in the data resulting from error correction (whether it is Error Free), but Reed-Solomon. Can detect whether an error remains (whether it is Error Free). CRC is an error detector and cannot correct errors, but Reed-Solomon can perform error correction on data with data errors up to the upper limit of its own correction capability. , It has the feature that it can guarantee Error Free. Therefore, in a system equipped with Reed-Solomon, the DRC function can be switched on / off based on the Reed-Solomon result (whether or not it is Error Free) rather than judging the data integrity based on the CRC value of MPEG data. It is reasonable and easy to judge.

  The preferred embodiment of the present invention has been described in detail above, but the present invention is not limited to the specific embodiment, and various modifications can be made within the scope of the present invention described in the claims. Deformation / change is possible.

10: DAB receiver 12: Antenna 14: Front end 16: A / D converter 20: Signal processing unit 21: Orthogonal demodulation unit 22: FFT 23: Error correction unit 24: Decoder 25: Volume control unit 30: D / A converter 32: Amplifier 34: Speaker 40: Controller 42: Input unit 44: Display unit 46: Memory

Claims (10)

A receiving device for receiving a compression-coded digital audio signal including audio data and control data for controlling the volume of the audio data,
Receiving means for receiving the digital audio signal;
Volume control means for controlling the volume when the audio data is output based on the control data contained in the received digital audio signal;
Voice output means for outputting voice based on the digital voice signal whose volume is controlled by the volume control means,
The volume control means includes
Guessing means for guessing the volume of the received audio data;
Setting means for setting an allowable range of control data based on the estimated volume;
Determining means for determining whether or not the control data is included in the allowable range;
Correction means for correcting the control data when the control data is determined to be outside the allowable range;
The volume control means controls the volume based on the control data when the control data is determined to be within the allowable range, and is corrected when the control data is determined to be outside the allowable range. A receiving device that controls the sound volume based on the control data. The receiving apparatus further includes error detection means for detecting an error of the digital audio signal based on an error detection code included in the received digital audio signal,
The volume control means controls the volume using the control data when no error is detected by the detection means, and stops the volume control based on the control data when an error is detected by the detection means. The receiving apparatus according to claim 1. The receiving device according to claim 1, wherein the estimation unit estimates a volume of the audio data based on a sum of data relating to amplitudes of respective frequency bands of the received audio data. The receiving device according to claim 1 or 2, wherein the estimating means estimates the volume of the audio data based on data relating to the maximum amplitude among the data relating to the amplitude of each frequency band of the received audio data. The receiving device according to claim 1, wherein the estimation unit estimates a volume of the audio data based on an average of data relating to amplitudes of respective frequency bands of the received audio data. The receiving device according to claim 1, wherein the estimation unit estimates a volume of the audio data based on a total of data regarding amplitudes of a certain level or more among data regarding amplitudes of each frequency band of the received audio data. . The receiving apparatus according to claim 3, wherein the amplitude-related data is a scale factor included in a compressed digital audio signal. The correction means corrects the control data to the lower limit value when the control data is smaller than a lower limit value of the allowable range, and controls the control data when the control data is larger than the upper limit value of the allowable range. The receiving apparatus according to claim 1, wherein data is corrected to the upper limit value. The receiving device further includes reception state determination means for determining whether or not the reception state is good based on data relating to the electric field strength of the received digital audio signal,
The volume control means controls the volume using the control data when no error is detected by the detection means and the reception state determination means determines that the reception state is good, and the detection means The receiving apparatus according to claim 2, wherein when the error is detected or the reception state determination unit determines that the reception state is not good, the control of the sound volume by the control data is stopped. The receiving apparatus according to claim 1, wherein the control data is DRC data.

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