Abstract:
[Problem] In a system that transmits content data from a content replay device to a content output device, to prevent a deterioration in audio quality or video data picture quality while being able to increase the simplicity of a setting-altering operation without requiring complicated signal processing. [Solution] The present invention is provided with: the content replay device, which receives an operation clock signal transmitted from the content output device via an operation clock transmission cable, operates on the basis of the operation clock signal, and transmits content data replayed by a replay unit to the content output device via a multimedia transmission cable; and the content output device, which generates the operation clock signal transmitted to the content replay device on the basis of an output device operation clock signal, transmits the operation clock signal to the content replay device via the operation clock transmission cable, and receives, performs signal processing on, and outputs to an external device the content data transmitted from the content replay device via the multimedia transmission cable.

Description:
TECHNICAL FIELD 
     The present invention relates to a content data transmission system for transmitting content data between a content reproduction apparatus (such as disc player) and a content output apparatus. 
     BACKGROUND ART 
     There is a system including a content reproduction apparatus (such as a disc player) for reproducing content data (such as video data and audio data) recorded on a recording medium such as a digital versatile disc (DVD) and a Blu-ray Disc (BD) or downloaded via a network from a server or the like, and a content output apparatus (such as an amplifier) for receiving digital data reproduced and output by the content reproduction apparatus, amplifying audio data of the digital data, and outputting the audio data to a speaker, and outputting the audio data and video data to a display apparatus such as a monitor or a television set. 
     In recent years, a digital interface such as the Institute of Electrical and Electronic Engineers (IEEE) 1394 interface or the High-Definition Multimedia Interface (HDMI) used for the transmission of the content data from the content reproduction apparatus to the content output apparatus is used in this system, and the audio data and the video data reproduced by the content reproduction apparatus can be transmitted as high quality digital data to the content output apparatus. 
     In the system for transmitting the content data from the content reproduction apparatus to the content output apparatus by using the digital interface, a master clock generated by a clock generation part of the content output apparatus and a master clock generated by a clock generation part of the content reproduction apparatus are not synchronized with each other. Therefore, a jitter is generated in the content data (digital data) received from the content reproduction apparatus, and the content output apparatus thus cannot correctly demodulate the received digital data, and hence noise is generated on an audio signal output from a speaker, the audio signal is interrupted, or an image quality of the video signal degrades. 
     As a method of synchronizing the master clocks of the content reproduction apparatus and the content output apparatus with each other, Patent Literature 1 discloses a method (transmission apparatus clock control mode) involving generating, by the content output apparatus, a master clock synchronized with the audio data transmitted from the content reproduction apparatus, and demodulating the audio data transmitted from the reproduction apparatus by using the master clock. 
     Moreover, as another method, Patent Literature 2 discloses a method (reception apparatus clock control mode) involving detecting, by the content output apparatus, whether the master clock generated by the clock generation part and the digital data transmitted from the content reproduction apparatus are synchronized with each other, or not, generating correction information for correcting a loss of the synchronization between the generated master clock and the audio data, and transmitting the correction information to the content reproduction apparatus. In this method, the content reproduction apparatus adjusts the frequency of the master clock based on the correction information received from the content output apparatus, encodes the audio data by using the adjusted master clock, and transmitting the encoded audio data to the content output apparatus. 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] JP 06-296173 A 
         [PTL 2] JP 2003-32572 A 
       
    
     SUMMARY OF INVENTION 
     Technical Problems 
     In the method (transmission apparatus clock control mode) involving generating, by an amplification apparatus, the master clock synchronized with the master clock of the reproduction apparatus, thereby synchronizing the master clocks of the reproduction apparatus and the amplification apparatus with each other, which is disclosed in Patent Literature 1, a phase locked loop (PLL) circuit using a clock oscillated from a voltage controlled oscillator (VCO) circuit is used to generate the master clock in the amplification apparatus. The VCO circuit has a permissible range of the clock synchronization of ±1,000 ppm (parts per million) with respect to a center frequency of the clock, and hence a jitter is generated in the generated master clock. Therefore, there is such a problem that, when the audio data transmitted from the reproduction apparatus is demodulated by using the master clock generated by the VCO circuit in the amplification apparatus, a jitter is generated in the audio data, and a sound quality of the audio data output from the amplification apparatus degrades. Moreover, this situation leads to degradation in image quality in a case of the video data. 
     In the method (reception apparatus clock control mode) involving adjusting the frequency of the master clock of the reproduction apparatus so as to synchronize with the master clock generated by the amplification apparatus, thereby synchronizing the master clocks of the reproduction apparatus and the amplification apparatus with each other, which is disclosed in Patent Literature 2, the amplification apparatus makes the adjustment so that the master clock of the reproduction apparatus synchronizes with the master clock of the amplification apparatus. The audio data transmitted from the reproduction apparatus is synchronized with the master clock of the amplification apparatus, and hence a jitter is not generated in the audio data received from the reproduction apparatus in the amplification apparatus. Thus, the amplification apparatus can reproduce the audio data received from the reproduction apparatus at a high sound quality. However, the master clock of the reproduction apparatus for the audio transmission is synchronized with the master clock of the amplification apparatus, and hence, for example, there occurs such a problem that the master clock for video and the master clock for audio cannot be synchronized in the reproduction apparatus, resulting in a momentary stop of a motion picture of the reproduced video data or a reproduction while an image corresponding to one frame is skipped. 
     In other words, if the master clocks of the content reproduction apparatus and the content output apparatus are synchronized with each other in the reception apparatus clock control mode in the system for transmitting the content data between the content reproduction apparatus and the content output apparatus by using the conventional digital interface, when a recording medium recording only audio data such as the DVD-AUDIO or the Compact Disc-Digital Audio (CD-DA) is reproduced, the content output apparatus can reproduce the audio data received from the content reproduction apparatus at a high sound quality. However, when a recording medium recording audio data and video data such as the DVD-VIDEO is reproduced, such problems as the momentary stop of the motion picture of the reproduced video data and the reproduction while an image corresponding to one frame is skipped occur. 
     On the other hand, if the master clocks of the reproduction apparatus and the amplification apparatus are synchronized with each other in the transmission apparatus clock control mode, when a recording medium recording audio data and video data is reproduced, such problems as the momentary stop of the motion picture of the reproduced video data and the reproduction while an image corresponding to one frame is skipped can be prevented from occurring. However, the content output apparatus demodulates the audio data transmitted from the content reproduction apparatus by using the master clock generated by the VCO circuit, and hence such a problem that a jitter is generated in the audio data and the sound quality of the audio data degrades occurs. 
     As described above, in the system for transmitting the content data such as the video data and the audio data by using the digital interface from the content reproduction apparatus to the content output apparatus, if only the audio data as well as both the audio data and the video data are transmitted from the content reproduction apparatus, there are such problems that a large number of circuits need to be added, that the complex signal processing needs to be applied, and that the sound quality of the audio data and the image quality of the video data degrade. 
     Moreover, if the reception apparatus clock control mode and the transmission apparatus clock control mode are used, it is necessary to check whether the content reproduction apparatus and the content output apparatus are compatible with these modes, which, in turn, requires checking whether the apparatus are compatible with these modes by means of mutual communication between both the apparatus, resulting in complex communication steps, and addition of circuits and programs. 
     Moreover, when these modes are selected, a user needs to change setting of the content reproduction apparatus and the content output apparatus so that those apparatus are compatible with the respective modes. It is relatively easy for a user who knows the modes well to carry out the setting, but it may be difficult for a user who does not know the modes well to carry out the setting. Further, both of the apparatus are respectively operated for setting the modes, and the operation thus takes time and labor. 
     In view of above-mentioned problems, the present invention has an object to eliminate necessity of the addition of a large number of circuits and complex signal processing, to simplify an operation for changing a setting by a user, and to transmit the data without degrading the sound quality of the audio data and the image quality of the video data in a system for transmitting content data such as video data and audio data from a content reproduction apparatus to a content output apparatus by using a digital interface. 
     Solution to Problems 
     According to the invention as claimed in claim  1  of this application, there is provided a content data transmission system including: a content reproduction apparatus for reproducing content data; and a content output apparatus for inputting the content data reproduced by the content reproduction apparatus, applying signal processing to the content data, and outputting the content data, in which: the content reproduction apparatus includes: a reproduction apparatus reference operation clock generation part for generating a reproduction apparatus reference operation clock signal; an operation clock reception part for receiving an operation clock signal transmitted from the content output apparatus via an operation clock transmission cable, and outputting a received operation clock signal synchronized with the operation clock signal; a reproduction apparatus operation clock conversion part for converting any one of the reproduction apparatus reference operation clock signal and the received operation clock signal into a reproduction apparatus operation clock signal; a content reproduction part for operating based on the reproduction apparatus operation clock signal, and reproducing the content data; a data output part for operating based on the reproduction apparatus operation clock signal, and transmitting the content data via a multimedia transmission cable to the content output apparatus; and a reproduction apparatus control part for controlling the overall content reproduction apparatus, and controlling the reproduction apparatus operation clock signal; and the content output apparatus includes: an output apparatus reference operation clock generation part for generating an output apparatus reference operation clock signal; an operation clock transmission part for generating the operation clock signal to be transmitted to the content reproduction apparatus based on the output apparatus reference operation clock signal, and transmitting the operation clock signal via the operation clock transmission cable to the content reproduction apparatus; a data input part for operating based on the output apparatus reference operation clock signal, and inputting the content data transmitted from the content reproduction apparatus via the multimedia transmission cable; an output part for operating based on the output apparatus reference operation clock signal and outputting the content data to an outside; and an output apparatus control part for controlling the overall content output apparatus, and providing control to transmit, to the content reproduction apparatus, the operation clock signal synchronized with the output apparatus reference operation clock signal from the operation clock transmission part. 
     According to the invention as claimed in claim  2  of this application, in the content data transmission system according to claim  1 , when the reproduction apparatus control part detects connection of the multimedia transmission cable, the reproduction apparatus control part checks whether or not the content output apparatus is compatible with an output apparatus clock operation mode in which the content reproduction apparatus operates based on the output apparatus reference operation clock signal, and when the content output apparatus is compatible with the output apparatus clock operation mode, controls the content reproduction apparatus so that the content reproduction apparatus operates in the output apparatus clock operation mode, and when the output apparatus control part of the content output apparatus confirms that the content reproduction apparatus is compatible with the output apparatus clock operation mode, the output apparatus control part provides control to automatically transmit the operation clock signal to the content reproduction apparatus. 
     According to the invention as claimed in claim  3  of this application, in the content data transmission system according to claim  1  or  2 , the reproduction apparatus control part controls, when the operation clock reception part receives the operation clock signal from the content output apparatus, the reproduction apparatus operation clock conversion part so that the reproduction apparatus operation clock conversion part converts the received operation clock signal output by the operation clock reception part into the reproduction apparatus operation clock signal, and controls, when the operation clock reception part fails to receive the operation clock signal from the content output apparatus within a predetermined period, the reproduction apparatus operation clock conversion part so that the reproduction apparatus operation clock conversion part converts the reproduction apparatus reference operation clock signal generated by the reproduction apparatus reference operation clock generation part into the reproduction apparatus operation clock signal. 
     According to the invention as claimed in claim  4  of this application, there is provided a content data transmission system including: a content reproduction apparatus for reproducing content data; and a content output apparatus for applying signal processing to the content data reproduced and transmitted by the content reproduction apparatus, and outputting the content data, in which: the content reproduction apparatus includes: a reproduction apparatus reference operation clock generation part for generating a reference operation clock signal; a reproduction apparatus data input/output part for operating based on a reproduction apparatus operation clock signal, outputting the content data via a multimedia transmission cable, receiving an operation clock signal transmitted from the content output apparatus via the multimedia transmission cable, and outputting a received operation clock signal synchronized with the operation clock signal; a reproduction apparatus operation clock conversion part for converting any one of the reference operation clock signal generated by the reproduction apparatus reference operation clock generation part and the received operation clock signal output by the reproduction apparatus data input/output part into a reproduction apparatus operation clock signal; a content generation part for operating based on the reproduction apparatus operation clock signal, and generating the content data; and a reproduction apparatus control part for controlling the overall content reproduction apparatus, and controlling the reproduction apparatus operation clock signal; the content output apparatus includes: an output apparatus reference operation clock generation part for generating a reference operation clock signal; an output apparatus data input/output part for generating the operation clock signal to be transmitted to the content reproduction apparatus based on the reference operation clock signal generated by the output apparatus reference operation clock generation part, transmitting the operation clock signal via the multimedia transmission cable to the content reproduction apparatus, operating based on the output apparatus reference operation clock signal, and inputting the content data transmitted from the content reproduction apparatus via the multimedia transmission cable; an output part for operating based on the reference operation clock signal generated by the output apparatus reference operation clock generation part, and outputting the content data to an outside; and an output apparatus control part for controlling the overall content output apparatus, and providing control to transmit, to the content reproduction apparatus, the operation clock signal synchronized with the output apparatus reference operation clock signal from the output apparatus data input/output part; and the reproduction apparatus control part controls, when the reproduction apparatus data input/output part receives the operation clock signal from the content output apparatus, the reproduction apparatus operation clock conversion part so that the reproduction apparatus operation clock conversion part converts the received operation clock signal output by the reproduction apparatus data input/output part into the reproduction apparatus operation clock signal, and controls, when the reproduction apparatus data input/output fail to receive the operation clock signal from the content output apparatus within a predetermined period, the reproduction apparatus operation clock conversion part so that the reproduction apparatus operation clock conversion part converts the reproduction apparatus reference operation clock signal generated by the reproduction apparatus reference operation clock generation part into the reproduction apparatus operation clock signal. 
     According to the invention as claimed in claim  5  of this application, in the content data transmission system according to claim  4 , the multimedia transmission cable is a High-Definition Multimedia Interface (HDMI) cable, and the reproduction apparatus data input/output part and the output apparatus data input/output part are HDMI data input/output parts, and the operation clock signal is transmitted over an Audio Return Channel (ARC) transmission line of the HDMI cable. 
     According to the invention as claimed in claim  6  of this application, there is provided a method of connecting a content reproduction apparatus for reproducing content data and a content output apparatus for inputting the content data reproduced by the content reproduction apparatus, applying signal processing to the content data, and outputting the content data to each other via a multimedia data transmission cable for transmitting the content data and an operation clock transmission cable for transmitting an operation clock signal, thereby transmitting the content data from the content data reproduction apparatus to the content output apparatus, the method including: a step of checking, when connection of the multimedia data transmission cable is detected, whether the content output apparatus is compatible with an output apparatus clock operation mode in which the content reproduction apparatus operates based on an output apparatus reference operation clock signal of the content output apparatus; a step of changing, when the content output apparatus is compatible with the output apparatus clock operation mode, setting in the content reproduction apparatus so as to operate in the output apparatus clock operation mode; a step of generating an operation clock signal based on an output apparatus reference operation clock signal, and transmitting the operation clock signal via the operation clock transmission cable to the content reproduction apparatus; a step of receiving the operation clock signal transmitted via the operation clock transmission cable, and generating a received operation clock signal synchronized with the operation clock signal; a step of converting the received operation clock signal into a reproduction apparatus operation clock signal; a step of operating based on the reproduction apparatus operation clock signal, and reproducing the content data; a step of transmitting the content data via the multimedia transmission cable to the content output apparatus; a step of receiving the content data transmitted from the content reproduction apparatus via the multimedia transmission cable; and a step of operating based on the output apparatus reference operation clock signal, and outputting the content data to an outside. 
     According to the invention as claimed in claim  7  of this application, there is provided a method of connecting between a content reproduction apparatus for reproducing content data and a content output apparatus for inputting the content data reproduced by the content reproduction apparatus, applying signal processing to the content data, and outputting the content data to each other via a multimedia data transmission cable for transmitting the content data and an operation clock transmission cable for transmitting an operation clock signal, thereby transmitting the content data from the content data reproduction apparatus to the content output apparatus, the method including: a step of generating, by the content reproduction apparatus, a reproduction apparatus reference operation clock signal; a step of receiving, by the content reproduction apparatus, an operation clock signal transmitted from the content output apparatus via the operation clock transmission cable, and outputting a received operation clock signal synchronized with the operation clock signal; a step of converting, by the content reproduction apparatus, any one of the reproduction apparatus reference operation clock signal and the received operation clock signal into a reproduction apparatus operation clock signal; a step of operating, by the content reproduction apparatus, based on the reproduction apparatus operation clock signal, and reproducing the content data; a step of operating, by the content reproduction apparatus, based on the reproduction apparatus operation clock signal, and transmitting the content data via the multimedia transmission cable to the content output apparatus; a step of controlling, by the content reproduction apparatus, the overall content reproduction apparatus, and controlling the reproduction apparatus operation clock signal; a step of generating, by the content output apparatus, an output apparatus reference operation clock signal; a step of generating, by the content output apparatus, the operation clock signal to be transmitted to the content reproduction apparatus based on the output apparatus reference operation clock signal, and transmitting the operation clock signal via the operation clock transmission cable to the content reproduction apparatus; a step of operating, by the content output apparatus, based on the output apparatus reference operation clock signal, and inputting the content data transmitted from the content reproduction apparatus via the multimedia transmission cable; a step of operating, by the content output apparatus, based on the output apparatus reference operation clock signal, and outputting the content data to an outside; a step of controlling, by the content output apparatus, the overall content output apparatus, and providing control to transmit, to the content reproduction apparatus, the operation clock signal synchronized with the output apparatus reference operation clock signal from an operation clock transmission part; and a step of controlling, by the content reproduction apparatus, when receives the operation clock signal from the content output apparatus, so that the reproduction apparatus operation clock conversion part convert the received operation clock signal output by the operation clock reception part into the reproduction apparatus operation clock signal, and controlling, when the operation clock reception part fails to receive the operation clock signal from the content output apparatus within a predetermined period, the reproduction apparatus operation clock conversion part so that the reproduction apparatus operation clock conversion part converts the reproduction apparatus reference operation clock signal generated by the reproduction apparatus operation clock signal. 
     According to the invention as claimed in claim  8  of this application, there is provided a method of connecting a content reproduction apparatus for reproducing content data and a content output apparatus for applying signal processing to the content data reproduced and transmitted by the content reproduction apparatus, and outputting the content data to each other via a multimedia data transmission cable for transmitting the content data and an operation clock signal, thereby transmitting the content data from the content data reproduction apparatus to the content output apparatus, the method including: a step of generating, by the content reproduction apparatus, a reproduction apparatus reference operation clock signal; a step of generating, by the content output apparatus, an output apparatus reference operation clock signal; a step of generating, based on the output apparatus reference operation clock signal, an operation clock signal synchronized with the output apparatus reference operation clock signal to be transmitted from the content output apparatus to the content reproduction apparatus, and transmitting the operation clock signal via the multimedia transmission cable to the content reproduction apparatus; a step of receiving, by the content reproduction apparatus, the operation clock signal transmitted from the content output apparatus via the multimedia operation clock transmission cable, and outputting a reproduction apparatus received operation clock signal synchronized with the operation clock signal; a step of converting any one of the reproduction apparatus reference operation clock signal and the reproduction apparatus received operation clock signal into a reproduction apparatus operation clock signal; a step of operating based on the reproduction apparatus operation clock signal, and reproducing the content data; a step of operating based on the reproduction apparatus operation clock signal, and transmitting the reproduced content data via the multimedia transmission cable to the content output apparatus; a step of operating, by the content output apparatus, based on the output apparatus reference operation clock signal, and inputting the content data transmitted from the content reproduction apparatus via the multimedia transmission cable; and a step of operating based on the output apparatus reference operation clock signal, and outputting the content data to an outside, in which the step of converting any one of the reproduction apparatus reference operation clock signal and the reproduction apparatus received operation clock signal into the reproduction apparatus operation clock signal includes converting, when the content reproduction apparatus receives the operation clock signal from the content output apparatus, the reproduction apparatus received operation clock signal into the reproduction apparatus operation clock signal, and converting, when the content reproduction apparatus fails to receive the operation clock signal from the content output apparatus within a predetermined period, the reproduction apparatus reference operation clock signal into the reproduction apparatus operation clock signal. 
     Advantageous Effects of Invention 
     According to the inventions of this application, in the system for transmitting the digital data such as the video data and the audio data from the content reproduction apparatus to the content output apparatus by using the digital interface, it is possible to eliminate necessity of the addition of a larger number of circuits and the complex signal processing to simplify the operation for changing the setting by the user, and to transmit the data without degrading the sound quality of the audio data and the image quality of the video data. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a schematic configuration of a content data transmission system according to a first embodiment of the present invention. 
         FIG. 2  is a diagram illustrating mode check processing in the content data transmission system according to the first embodiment of the present invention. 
         FIG. 3  is a flowchart illustrating processing relating to content data transmission in the content data transmission system according to the first embodiment of the present invention. 
         FIG. 4  is a diagram illustrating a schematic configuration of a content data transmission system according to a second embodiment of the present invention. 
         FIG. 5  is a flowchart illustrating processing relating to the content data transmission in the content data transmission system according to the second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     Now, a description is given of a first embodiment of the present invention with reference to the accompanying drawings. 
       FIG. 1  is a diagram illustrating a schematic configuration of a content data transmission system according to the first embodiment of the present invention. 
     In  FIG. 1 , a content data transmission system  100  includes a content reproduction apparatus  200  and a content output apparatus  300 . 
     The content reproduction apparatus  200  is, for example, a disc player such as a DVD player and a BD player, a memory player for reproducing content data stored in a semiconductor memory, and a network player, which is connected to a network, for downloading digital data via the network from a server or the like. The content reproduction apparatus  200  applies signal processing such as decoding to video data and audio data reproduced from a recording medium such as a disc, or video data and audio data acquired via a network, and outputs the video data and the audio data as digital data. 
     Moreover, the content output apparatus  300  is, for example, an audio visual (AV) amplifier, an AV receiver, and a network receiver. The content output apparatus  300  applies amplification for an audio signal, signal processing for the surround, signal processing for converting the video data into a video signal which can be displayed on a television set or a monitor, and the like to the video data and the audio data input from an external apparatus directly connected via wires to the content output apparatus  300  or input via a network, and outputs the resultant signal as digital data. 
     Moreover, the content data is data such as video data, audio data, and a computer program. In this embodiment, a description is given while assuming that the content data is data including video data and audio data. 
     The content reproduction apparatus  200  and the content output apparatus  300  are connected to each other via a multimedia data transmission cable  400  and an operation clock transmission cable  500  in the content data transmission system  100  according to this embodiment. The content reproduction apparatus  200  and the content output apparatus  300  are connected to each other via the multimedia transmission cable  400  for transmitting the content data. An HDMI cable  400  is used as the multimedia transmission cable  400  for transmitting the content data in this embodiment. A data output part of the content reproduction apparatus  200  and a data input part of the content output apparatus  300  have an interface function compliant with the HDMI, and apparatus authentication and protection of data transfer between the content reproduction apparatus  200  and the content output apparatus  300  can be carried out, and the audio data and the video data can be transmitted over a single cable by using the HDMI cable  400 . 
     Moreover, the content reproduction apparatus  200  and the content output apparatus  300  are connected to each other via the operation clock transmission cable  500  for transmitting an operation clock signal. In this embodiment, a cable compliant with the SPDIF (SPDIF cable  500 ) is used as the operation clock transmission cable. The data output part of the content reproduction apparatus  200  and the data input part of the content output apparatus  300  have an SPDIF interface function. The SPDIF interface is generally used for transmitting audio data, and can be used inexpensively without a complex circuit configuration. 
     In this embodiment, the operation clock transmission cable  500  (SPDIF cable  500 ) is intended to transmit the operation clock signal from the content output apparatus  300  to the content reproduction apparatus  200 , and an operation clock signal based on a reference operation clock signal generated by a reference operation clock generation part of the content output apparatus  300  is thus used as a transmission clock for the SPDIF cable  500 , and 0 data is transmitted as the audio data. As a result, the content reproduction apparatus  200  does not need to carry out processing such as decoding for unnecessary audio data, and can receive precisely the operation clock signal generated by the content output apparatus  300 . 
     The operation clock transmission cable  500  is used to transmit the operation clock signal from the content output apparatus  300  to the content reproduction apparatus  200  in this embodiment, but the HDMI cable  400  may be used. A data line not used in the HDMI cable  400  may be used to transmit the operation clock signal from the content output apparatus  300  to the content reproduction apparatus  200 . Further, a power supply cable for supplying the content reproduction apparatus  200  and the content output apparatus  300  with an electric power may be used. With this, the operation clock transmission cable, and connection parts and interface parts of this cable can be omitted to simplify a circuit configuration. 
     A description is now given of configurations of the content reproduction apparatus and the content output apparatus of this embodiment. First, a description is given of the content reproduction apparatus  200 . 
     The content reproduction apparatus  200  includes a reproduction apparatus reference operation clock generation part  210 , an operation clock reception part  220 , a reproduction apparatus operation clock conversion part  230 , a content generation part  240 , a reproduction apparatus signal processing part  250 , a data output part  260 , and a reproduction apparatus control part  270 . 
     The reproduction apparatus reference operation clock generation part  210  includes a crystal oscillator (not shown), and generates a reference operation clock signal serving as a reference of an operation clock signal for operating respective parts in the content reproduction apparatus  200 . The reference operation clock signal is output to the reproduction apparatus operation clock conversion part  230 . 
     The operation clock reception part  220  receives the operation clock signal transmitted from an operation clock transmission part  350 , which is described later, of the content output apparatus  300  via the SPDIF cable  500 , converts the frequency of the received operation clock signal into a predetermined frequency by means of an integrated frequency converter (not shown), and outputs the operation clock signal (received operation clock signal), to which the frequency conversion is applied, to the reproduction apparatus operation clock conversion part  230 . Specifically, the operation clock reception part  220  receives an operation clock signal at 48 kHz from the content output apparatus, converts the operation clock signal into an operation clock signal at 24 MHz by means of the integrated frequency converter, and outputs the operation clock signal at 24 MHz to the reproduction apparatus operation clock conversion part  230 . 
     The reproduction apparatus operation clock conversion part  230  receives an input of the reference operation clock signal output from the reproduction apparatus reference operation clock generation part  210  or the received operation clock signal output from the operation clock reception part  220 , converts, based on control by the reproduction apparatus control part  270 , which is described later, any one of the operation clock signals into the operation clock signal at a predetermined frequency, and outputs the converted operation clock signal to the content generation part  240 , the signal processing part  250 , the data output part  260 , and the like, which are described later. 
     The reproduction apparatus operation clock conversion part  230  includes a first frequency conversion part (not shown), a second frequency conversion part (not shown), and a signal switching part (not shown). The first frequency conversion part is a frequency converter which is high in input frequency gain and compatible with a signal large in frequency variation. The second frequency conversion part is a frequency converter which is low in input frequency gain and compatible with a signal relatively small in frequency variation, and can convert the signal into an operation clock signal having a frequency small in error with respect to a predetermined frequency. The signal switching part switches between the reference operation clock signal output from the reproduction apparatus reference operation clock generation part  210  and the received operation clock signal output from the operation clock reception part  220 , which are input to the reproduction apparatus operation clock conversion part  230 , based on control by the reproduction apparatus control part  270  described later. 
     Specifically, the signal switching part switches the input source to any one of the received operation clock signal at 24 MHz output from the operation clock reception part  220  and the reference operation clock signal at 24 MHz generated by the reproduction apparatus reference operation clock generation part  210  based on the control by the reproduction apparatus control part  270  in the reproduction apparatus operation clock conversion part  230 . The first frequency conversion part converts the input operation clock signal at 24 MHz into the operation clock signal at 13.5 MHz, and outputs the operation clock signal at 13.5 MHz to the second frequency conversion part. The second frequency conversion part further converts the operation clock signal at 13.5 MHz into an operation clock signal at 27 MHz, and outputs the operation clock signal to the content generation part  240 , the reproduction apparatus signal processing part  250 , the data output part  260 , and the like. Note that, the first frequency conversion part may convert the input operation clock signal at 24 MHz into an operation clock signal at 27 MHz, and may output the operation clock signal at 27 MHz to the second frequency conversion part, and the second frequency conversion part may further convert the operation clock at 27 MHz into the operation clock signal at 27 MHz. 
     The operation clock signal at 24 MHz input from the operation clock reception part  220  is the received operation clock signal generated based on the operation clock signal at 48 kHz transmitted via the SPDIF cable  500 , and is a signal large in frequency variation with respect to the reference frequency. Therefore, the first frequency conversion part high in input frequency gain converts the operation clock signal into the operation clock signal narrow in frequency variation range with respect to the frequency serving as the reference. Specifically, the operation clock signal at 24 MHz is converted into the operation clock signal having a frequency range of 13.5 MHz±5%. Then, the operation clock signal in the frequency range of 13.5 MHz±5% output from the first frequency conversion part is converted into the operation clock signal narrower in frequency variation range with respect to the predetermined frequency and high in precision by the second frequency conversion part low in input frequency gain. Specifically, the operation clock signal in the frequency range of 13.5 MHz±5% is converted into the operation clock signal in a frequency range of 27 MHz±0.5%, and the operation clock signal is output to the content generation part  240 , the reproduction apparatus signal processing part  250 , the data output part  260 , and the like. The content generation part  240 , the reproduction apparatus signal processing part  250 , the data output part  260 , and the like operate in synchronization with the operation clock signal small in error with respect to the predetermined frequency. Therefore, the content generation part  240 , the reproduction apparatus signal processing part  250 , the data output part  260 , and the like operate without a loss in synchronization and the like. 
     The content generation part  240  reads content data recorded on a disc, or content data stored in a semiconductor memory, and outputs the content data to the reproduction apparatus signal processing part  250  on a subsequent stage. Moreover, the content generation part  240  includes a network connection part (not shown), acquires the content data by downloading the content data stored in a server or the like via a network, or receiving a stream of the content data, and outputs the content data to the reproduction apparatus signal processing part  250  on the subsequent stage. 
     The reproduction apparatus signal processing part  250  applies various signal processing such as decode processing to the content data input from the content generation part  240 . For example, the reproduction apparatus signal processing part  250  applies the decode processing to the audio data and the video data, multi-channel processing to the audio data, and processing such as 3D conversion to the video data. 
     The data output part  260  converts the content data output from the reproduction apparatus signal processing part  250  into data in a data format which can be transmitted on the cable connected between the content reproduction apparatus  200  and the content output apparatus  300 , and outputs the converted content data in order to transmit the content data to the content output apparatus  300  on the following stage. The content reproduction apparatus  200  and the content output apparatus  300  are connected to each other via the HDMI cable  400  in this embodiment. The data output part  260  has an HDMI interface function, and converts data into data that matches the data transmission over the HDMI interface to transmit the content data via the HDMI cable  400  to the content output apparatus  300 . 
     The reproduction apparatus control part  270  controls the overall content reproduction apparatus  200 . The reproduction apparatus control part  270  provides control to convert the frequency of the operation clock signal in the reproduction apparatus operation clock conversion part  230  based on the operation clock signal received from the content output apparatus  300 , thereby operating the content generation part  240 , the reproduction apparatus signal processing part  250 , the data output part  260 , and the like based on the operation clock signal, and transmitting the content data to the content output apparatus  300 . 
     The reproduction apparatus control part  270  detects whether the operation clock signal can be received from the content output apparatus  300  based on turning on/off of a power supply, setting by a user, the connection of the HDMI cable  400 , and the like, and if the operation clock signal can be received from the content output apparatus  300 , controls the signal switching part of the reproduction apparatus operation clock conversion part  230  to generate the operation clock signal based on the received operation clock signal received by the operation clock reception part  220 , thereby controlling the respective parts in the apparatus to operate. Moreover, the reproduction apparatus control part  270  detects whether the operation clock signal can be received from the content output apparatus  300 , and if the reproduction apparatus control part  270  detects that the operation clock signal cannot be received from the content output apparatus  300 , controls the signal switching part of the reproduction apparatus operation clock conversion part  230  to generate the operation clock signal based on the reference operation clock signal output by the reproduction apparatus reference operation clock generation part  210 , thereby controlling the respective parts in the apparatus to operate. 
     A description is now given of the content output apparatus  300 . 
     The content output apparatus  300  includes a data input part  310 , an output apparatus signal processing part  320 , an output part  330 , an output apparatus reference operation clock generation part  340 , the operation clock transmission part  350 , and an output apparatus control part  360 . 
     The data input part  310  receives the content data transmitted via the HDMI cable  400  from the content reproduction apparatus  200 . The data input part  310  outputs the received content data to the output apparatus signal processing part  320  on a subsequent stage. 
     The output apparatus signal processing part  320  applies signal processing to the content data output from the data input part  310 , and outputs the processed content data to the output part  330 . The signal processing includes, for example, surround conversion processing for the audio data, and signal processing of superimposing an on-screen display (OSD) signal on the video data. 
     The output part  330  includes an amplification part (not shown) for amplifying the audio data, and a video encoder (not shown) for converting the video data into a video signal format for displaying the video data on a television set or a monitor. The output part  330  separates the content data output from the output apparatus signal processing part  320  into the video data and the audio data, and outputs the video data and the audio data. The audio data is output via the amplification part from output terminals to speakers or the like. The video data is output via the video encoder to a television set or a monitor. 
     The output apparatus reference operation clock generation part  340  includes a crystal oscillator (not shown), and generates the reference operation clock signal. The reference operation clock signal in this embodiment serves as a reference for the operation clock signal of the content output apparatus  300 , and as a reference for the operation clock signal to be transmitted to the content reproduction apparatus  200 . Specifically, the output apparatus reference operation clock generation part  340  generates a reference operation clock signal at 24 MHz, and outputs the reference operation clock signal to the data input part  310 , the output apparatus signal processing part  320 , the output part  330 , and the like. 
     The operation clock transmission part  350  converts the reference operation clock signal generated by the output apparatus reference operation clock generation part  340  to an operation clock signal at the predetermined frequency, and then transmits the operation clock signal via the SPDIF cable  500  to the content reproduction apparatus  200 . In this embodiment, the reference operation clock signal at 24 MHz generated by the output apparatus reference operation clock generation part  340  is converted into the operation clock signal having the frequency of 48 kHz, and the operation clock signal is transmitted via the SPDIF cable  500  to the content reproduction apparatus  200 . 
     The output apparatus control part  360  controls the overall content output apparatus  300 . The output apparatus control part  360  provides the control of transmitting the reference operation clock signal generated by the output apparatus reference operation clock generation part  340  from the operation clock transmission part  350  via the SPDIF cable  500  to the content reproduction apparatus  200 , and the control of receiving the content data transmitted from the content reproduction apparatus  200 , applying the signal processing to the content data and then, outputting the content data from the output part  330  to the outside. 
     A description is now given of the operation of the content reproduction apparatus  200  and the content output apparatus  300  according to this embodiment. 
     In this embodiment, both the apparatus operate in an output apparatus clock operation mode where the content reproduction apparatus  200  operates based on the operation clock signal generated by the content output apparatus  300 , and hence it is necessary for both the apparatus to mutually check whether both the apparatus are compatible with the output apparatus clock operation mode. 
     The output apparatus clock operation mode is valid only when both the content reproduction apparatus  200  and the content output apparatus  300  are compatible therewith, and the user can also set to turn on/off the output apparatus clock operation mode. The output apparatus clock operation mode is in the off state by default for the content reproduction apparatus  200  and the content output apparatus  300 . A description is given of an operation of automatically setting to turn on/off the output apparatus clock operation mode according to this embodiment. The operation mode may be checked when the power supply to the content reproduction apparatus or the content output apparatus is turned on. 
     When the HDMI cable  400  is connected between the content reproduction apparatus  200  and the content output apparatus  300 , and the power supply to the respective apparatus is turned on, or when the power supply is turned on, and then the HDMI cable  400  is connected between both the apparatus, the reproduction apparatus control part  270  or the output apparatus control part  360  carries out mode check processing based on the turning on of the power supply and the detection of the connection of the HDMI cable  400  via the HDMI interface. 
     A description is now given of the mode check processing. On this occasion, a description is given of such an example that the HDMI cable  400  is connected, and the Consumer Electronics Control (CEC) of the HDMI interface function is used as a communication method during the mode check processing. 
       FIG. 2  is a diagram illustrating the mode check processing in the content data transmission system according to the first embodiment of the present invention. 
     When the content reproduction apparatus  200  and the content output apparatus  300  are connected to each other via the HDMI cable  400 , the reproduction apparatus control part  270  of the content reproduction apparatus  200  detects that the HDMI cable  400  is connected, and carries out the mode check processing. The output apparatus control part  360  of the content output apparatus  300  also detects that the HDMI cable  400  is connected. 
     In the content reproduction apparatus  200 , the reproduction apparatus control part  270  uses the HDMI interface function of the data output part  260 , thereby transmitting apparatus information on the content reproduction apparatus  200  via the HDMI cable  400  to the content output apparatus  300 . The apparatus information is information for identifying the apparatus itself (such as a manufacturer name and a model number). On this occasion, the transmission of the apparatus information on the content reproduction apparatus  200  is not based on the CEC communication setting, but is carried out when the HDMI cable  400  is connected. 
     The content output apparatus  300  receives the apparatus information via the HDMI cable  400  by the data input part  310  from the content reproduction apparatus  200 . On this occasion, a table stored in an internal memory (not shown) is referred to based on the apparatus information from the received content reproduction apparatus  200 , and if the content reproduction apparatus is an apparatus from a predetermined manufacturer, the internal CEC communication setting is temporarily enabled independently of the CEC communication setting of the content output apparatus  300 . The output apparatus control part  360  uses the CEC function of the HDMI interface function of the data input part  310 , thereby transmitting, via the HDMI cable  400 , the apparatus information on the content output apparatus  300  to the content reproduction apparatus  200 . 
     On the other hand, when the data output part  260  receives the apparatus information from the content output apparatus  300  in the content reproduction apparatus  200 , the reproduction apparatus control part  270  refers to the table stored in the internal memory of the reproduction apparatus control part  270 , thereby checking whether the content output apparatus  300  is an apparatus from a predetermined manufacturer. 
     If the content output apparatus  300  is an apparatus from a predetermined manufacturer, the content reproduction apparatus  200  notifies the content output apparatus  300  of whether the content reproduction apparatus  200  itself is compatible with the output apparatus clock operation mode or not by means of the CEC function of the HDMI interface function. Simultaneously, the content output apparatus  300  checks the notified content from the content reproduction apparatus  200 , and notifies the content reproduction apparatus  200  of whether the content output apparatus  300  itself is compatible with the output apparatus clock operation mode or not by means of the CEC function of the HDMI interface function. 
     If the content reproduction apparatus  200  confirms that the content output apparatus  300  is compatible with the output apparatus clock operation mode, the content reproduction apparatus  200  transmits a request for starting the operation in this mode to the content output apparatus  300 . The content output apparatus  300  switches the setting to the output apparatus clock operation mode based on the request from the content reproduction apparatus  200 . The content output apparatus  300  switches the operation mode, and then, disables the internal CEC communication setting, which has been temporarily enabled. 
     On this occasion, the apparatus information can be acquired by the method of mutually communicating the apparatus information by means of the CEC function of the HDMI interface function of the HDMI cable  400  as well as a method of transmitting the apparatus information on the content reproduction apparatus  200  as the PACKET information on the HDMI, and transmitting the apparatus information on the content output apparatus  300  as the EDID information. Moreover, whether the apparatus is compatible with the output apparatus clock operation mode can be checked by transmitting the apparatus information on the content output apparatus  300  as the channel bit status information of the SPDIF output, and transmitting the apparatus information on the content reproduction apparatus  200  as the PACKET information on the HDMI. 
     When the content reproduction apparatus  200  receives information representing start of operation in the output apparatus clock operation mode from the content output apparatus  300 , the content reproduction apparatus  200  also changes its own setting to the output apparatus clock operation mode. On this occasion, the mode check processing is finished. When the mode check processing is finished, the content reproduction apparatus  200  and the content output apparatus  300  proceed to operations in the output apparatus clock operation mode. 
     A description is now given of processing of transmitting the content data between the content reproduction apparatus  200  and the content output apparatus  300 . 
       FIG. 3  is a flowchart illustrating the processing relating to the content data transmission in the content data transmission system according to the first embodiment of the present invention. 
     As described before, when the mode check processing is finished, the content reproduction apparatus  200  and the content output apparatus  300  are set to such a state that the content reproduction apparatus  200  and the content output apparatus  300  can operate in the output apparatus clock operation mode (Step  101 ). When the content output apparatus  300  becomes operable in the output apparatus clock operation mode, the content output apparatus  300  transmits such a notification that the operation clock signal is transmitted via the HDMI cable  400  to the content reproduction apparatus  200 , and starts the transmission of the operation clock signal via the SPDIF cable  500  (Step  102 ). 
     Specifically, in the content output apparatus  300 , the switch of the mode causes the operation clock transmission part  350  to generate the operation clock signal at 48 kHz based on the reference operation clock signal generated by the output apparatus reference operation clock generation part  340 , and to start the transmission of the operation clock via the SPDIF cable  500  to the content reproduction apparatus  200 . 
     The reproduction apparatus control part  270  of the content reproduction apparatus  200  checks whether the operation clock reception part  220  has received the operation clock signal at 48 kHz from the content output apparatus  300  or not (Step  103 ), and when the operation clock reception part  220  receives the operation clock signal, the operation clock reception part  220  converts the received operation clock signal into the received operation clock signal at 24 MHz, and outputs the converted operation clock signal to the reproduction apparatus operation clock conversion part  230  on the subsequent stage (Step  104 ). 
     On this occasion, if the operation clock reception part  220  cannot receive the operation clock signal from the content output apparatus  300  within a predetermined period due to a defect of the SPDIF cable  500  or the like after the operation in the output apparatus clock operation mode starts (Step  105 ), the reproduction apparatus control part  270  switches the output apparatus clock operation mode, and provides such control that the reproduction apparatus operation clock signal is generated based on the reference operation clock signal generated by the reproduction apparatus reference operation clock generation part  210  to operate the apparatus (Step  106 ). The predetermined period is, for example, approximately five seconds. 
     If the content reproduction apparatus  200  cannot receive the operation clock signal within the predetermined period from the content output apparatus  300 , the reproduction apparatus control part  270  controls the content reproduction apparatus  200  to operate based on the reproduction apparatus operation clock signal generated based on the reference operation clock signal in the content reproduction apparatus  200 , and thus such a case that the content data is not output from the content reproduction apparatus  200  for a long period does not occur. As a result, even if a transmission error of the operation clock signal occurs between the content reproduction apparatus  200  and the content output apparatus  300 , the user does not need to carry out a complex change in setting, and can listen to the content data via the content output apparatus  300 . 
     Moreover, if the setting is switched from the output apparatus clock operation mode due to the transmission error of the operation clock signal as described above, the reproduction apparatus control part  270  presents such a notification that the mode setting has been changed on a display part (not shown) of the content reproduction apparatus  200 , thereby notifying the user of the change. As a result, the user can recognize that the operation is not carried out in the output apparatus clock operation mode. Moreover, if such a defect that the SPDIF cable  500  is disconnected occurs, or a terminal of a connection destination is not correct, the user can recognize the situation. 
     The reproduction apparatus operation clock conversion part  230  generates the operation clock signal at 27 MHz (reproduction apparatus operation clock signal) synchronized with the received operation clock signal at 24 MHz, and outputs the operation clock signal to the content generation part  240 , the reproduction apparatus signal processing part  250 , and the data output part  260  (Step  107 ). 
     The content generation part  240  operates based on the operation clock signal supplied from the reproduction apparatus operation clock conversion part  230 , reads content data from a mounted disc or downloads content data via the network, and outputs the content data to the reproduction apparatus signal processing part  250  (Step  108 ). 
     The reproduction apparatus signal processing part  250  also operates based on the operation clock signal supplied from the reproduction apparatus operation clock conversion part  230 , applies predetermined signal processing to the content data input from the content generation part  240 , and outputs the content data to the data output part  260  (Step  109 ). 
     The data output part  260  also operates based on the operation clock signal supplied from the reproduction apparatus operation clock conversion part  230 , converts the content data input from the reproduction apparatus signal processing part  250  into content data in a predetermined signal format, and transmits the content data via the HDMI cable  400  to the content output apparatus  300  (Step  110 ). 
     The data input part  310  receives the content data output from the content reproduction apparatus  200 , converts the signal format into a predetermined format, and then outputs the content data to the output apparatus signal processing part  320  in the content output apparatus  300  (Step  111 ). The respective parts of the content output apparatus  300  (in  FIG. 1 , the data input part  310 , the output apparatus signal processing part  320 , and the output part  330  of the content output apparatus  300 ) operate based on the operation clock signal generated by the output apparatus reference operation clock generation part  340 . 
     The output apparatus signal processing part  320  applies predetermined signal processing to the content data output from the data input part  310 , and outputs the processed content data to the output part  330  (Step  112 ). The output part  330  amplifies the audio data, applies video encoding processing to the video data, and then outputs the audio data and the video data as the video signal and the audio signal, respectively, to the external apparatus (Step  113 ). 
     As described above, when the power supply of the content reproduction apparatus  200  and the content output apparatus  300  is turned on, or the HDMI cable  400  is connected, the content data transmission system  100  according to this embodiment automatically checks whether both the apparatus are compatible with the output apparatus clock operation mode or not, and, if the content data transmission system  100  confirms that both the apparatus are compatible with the mode, the content data transmission system  100  is automatically set to the output apparatus clock operation mode, and operates in the mode. As a result, the user does not need to set the mode each time the power supply is turned on or each time the HDMI cable  400  is connected, resulting in saving time. Moreover, because the mode is automatically set, the user does not make incorrect setting. Further, the operation is carried out in the output apparatus clock operation mode in which the content reproduction apparatus  200  operates based on the operation clock signal of the content output apparatus  300 . Thus, and the content data reproduced by the content reproduction apparatus  200  is output from the content output apparatus  300 , a jitter between both the apparatus is reduced, and the content data is transmitted without adverse effect on the data transmission. 
     Moreover, the content data transmission system  100  according to this embodiment transmits the signal representing that the content output apparatus  300  is compatible with the output apparatus clock operation mode, and, if the operation clock reception part  220  has not received the operation clock signal for the predetermined period (such as five seconds) after the signal is received, stops the output apparatus clock operation mode, switches the signal switching part of the reproduction apparatus operation clock conversion part  230 , generates the reproduction apparatus operation clock signal based on the reference operation clock signal generated by the reproduction apparatus reference operation clock generation part  210 , and operates based on the reproduction apparatus operation clock signal. As a result, even if an output error of the operation clock signal from the content output apparatus  300 , a disconnection of the cable, or a connection error of the cable occurs, such a state that the content data cannot be reproduced does not continue, and the reproduction of the content data becomes available in the content reproduction apparatus  200  in a short period. 
     A description has been given of the content data transmission system  100  according to this embodiment configured so that the mode check processing is carried out in order to check whether the content reproduction apparatus  200  and the content output apparatus  300  are each compatible with the output apparatus clock operation mode or not, but the content data transmission system  100  may be configured so that the mode check processing is not carried out, but data representing that the operation clock signal is output from the content output apparatus  300  is superimposed on the operation clock signal in order to check the reliability of the clock signal input to the operation clock reception part  220 , and only if the operation clock signal received on the content reproduction apparatus  200  side is superimposed with the data representing that the operation clock signal is output from the content output apparatus  300 , the content data transmission system  100  operates in the output apparatus clock operation mode. For example, if the operation clock transmission part  350  transmits the operation clock to the operation clock reception part  220 , the output apparatus control part  360  may control the operation clock transmission part  350  so as to transmit the operation clock signal superimposed with a predetermined bi-phase signal. The reproduction apparatus control part  270  may determine whether the predetermined bi-phase signal is superimposed on the operation clock received by the operation clock reception part  220 . If the bi-phase signal is superimposed, the reproduction apparatus control part  270  may provide control so as to operate in the output apparatus clock operation mode, and if the bi-phase signal is not superimposed, may switch the signal switching part of the reproduction apparatus operation clock conversion part  230  to generate the reproduction apparatus operation clock signal based on the reference operation clock signal generated by the reproduction apparatus reference operation clock generation part  210 , and may provide control so as to operate based on the reproduction apparatus operation clock signal. As a result, a circuit configuration required for the mode check processing can be omitted, and a time required for the mode check processing can be reduced. Moreover, even if an operation clock signal transmitted from an apparatus other than the content output apparatus  300  is received by any chance while the operation clock transmission cable  500  is connected to the apparatus other than the content output apparatus  300 , a jitter can be prevented from being generated on the audio data to be reproduced, and the sound quality and the image quality can be prevented from degrading. 
     In the content data transmission system  100  according to this embodiment, the operation clock transmission part  350  transmits the operation clock signal at 48 kHz to the operation clock reception part  220 , the operation clock signal at 27 MHz is generated from the operation clock signal at 48 kHz, the operation clock signal at 24 MHz, which is the operation clock signal for the 48 kHz system, and an operation clock signal at 22 MHz, which is the operation clock signal for a 44.1 kHz system, are generated from the operation clock signal at 27 MHz, but the content data transmission system  100  may be configured, for example, to switch and transmit the plurality of clock signals. For example, the operation clock transmission part  350  is configured so as to switch and transmit the operation clock signal at 48 kHz and the operation clock signal at 44.1 kHz, and the operation clock reception part  220  is configured to operate based on the received operation clock frequency. As a result, for example, when content data including video data recorded on a recording medium such as a DVD and a BD is reproduced, the switching can be made so as to operate based on the operation clock signal at 48 kHz, and when content data not including video data recorded on a recording medium such as a CD is reproduced, the switching can be made so as to operate based on the operation clock signal at 44.1 kHz, and hence an arbitrary operation clock is selected for operation out of the plurality of the operation clocks depending on content data to be reproduced. 
     A description has been given of the content data transmission system  100  according to this embodiment with the use of the values of frequency such as 24 MHz, 13.5 MHz, 27 MHz, 48 kHz, and 44.1 kHz as the frequency value of the operation clock signal, but a transmission system may use other arbitrary values of frequency as long as the effect described in this embodiment is provided. 
     Second Embodiment 
     A description is now given of a content data transmission system according to a second embodiment of the present invention. 
       FIG. 4  is a diagram illustrating a schematic configuration of the content data transmission system according to a second embodiment of the second embodiment of the present invention. 
     Note that, like configurations are denoted by like numerals as of the first embodiment throughout the drawings, and the descriptions thereof are omitted to facilitate understanding in the content data transmission system according to the second embodiment. 
     The content data transmission system  101  includes a content reproduction apparatus  201  and a content output apparatus  301 . 
     The content data is data such as video data, audio data, and a computer program. In this embodiment, a description is given while assuming that the content data is data including video data and audio data. 
     The content reproduction apparatus  201  is, for example, a disc reproduction apparatus such as a DVD player and a BD player, a memory player for reproducing content data stored in a semiconductor memory, and a network player for downloading digital data via the connected network from a server or the like. 
     The content reproduction apparatus  201  applies signal processing such as decoding to video data and audio data reproduced from a recording medium such as a disc, or video data and audio data acquired via a network, and outputs the video data and the audio data as digital data. 
     As the content output apparatus  301 , for example, an audiovisual (AV) amplifier, an AV receiver, and a network receiver are used. The content output apparatus  301  applies amplification for an audio signal, signal processing for the surround, signal processing for converting the video data into a video signal which can be displayed on a television set or a monitor, and the like to the video data and the audio data input from an external apparatus directly connected or via a network, and outputs the resultant signal as digital data. 
     The content reproduction apparatus  201  and the content output apparatus  301  are connected to each other via a multimedia data transmission cable  400 . The content reproduction apparatus  201  and the content output apparatus  301  are connected to each other via the multimedia data transmission cable  400  for transmitting the content data and the operation clock signal. An HDMI cable is used as the multimedia transmission cable  400  for transmitting the content data and the operation clock signal in this embodiment. A reproduction apparatus data input/output part of the content reproduction apparatus  201  and an output apparatus data input/output part of the content output apparatus  301  have an interface function compliant with the HDMI, and apparatus authentication and protection of data transfer between the content reproduction apparatus  201  and the content output apparatus  301  can be carried out by using the HDMI cable. The operation clock signal is converted into the operation clock signal in the SPDIF format, and is transmitted by the ARC transmission line in the HDMI cable. The reproduction apparatus data input/output part of the content reproduction apparatus  201  and the output apparatus data input/output part of the content output apparatus  301  include an SPDIF interface function for transmitting the operation clock signal as data in the SPDIF format on the ARC transmission line. The SPDIF interface is generally used for transmitting audio data, and can be used inexpensively without a complex circuit configuration. As described above, the audio data, the video data, and the operation clock signal can be transmitted over a single cable by using the HDMI cable. 
     According to this embodiment, when the operation clock signal is transmitted from the content output apparatus  301  to the content reproduction apparatus  201 , an operation clock signal based on the reference operation clock signal generated by the reference operation clock generation part of the content output apparatus  301  is used as the transmission clock. As a result, the content reproduction apparatus  201  does not need to carry out processing such as decoding for unnecessary audio data, and can receive precisely the operation clock signal generated by the content output apparatus  301 . 
     A description is now given of configurations of the content reproduction apparatus  201  and the content output apparatus according to this embodiment. 
     First, the content reproduction apparatus  201  includes a reproduction apparatus reference operation clock generation part  210 , a reproduction apparatus operation clock conversion part  230 , a content generation part  240 , a reproduction apparatus signal processing part  250 , a reproduction apparatus data input/output part  280 , an ARC reception part  280   a , and a reproduction apparatus control part  270 . 
     The reproduction apparatus reference operation clock generation part  210  includes a crystal oscillator (not shown), and generates a reference operation clock signal serving as a reference of an operation clock signal for operating respective parts in the content reproduction apparatus  201 . The reference operation clock signal is output to the reproduction apparatus operation clock conversion part  230 . 
     The reproduction apparatus operation clock conversion part  230  receives an input of the reference operation clock signal generated by the reproduction apparatus reference operation clock generation part  210  or the received operation clock signal received from the ARC reception part  280   a  described later, converts, based on control by the reproduction apparatus control part  270  described later, any one of the operation clock signals into the operation clock signal at a predetermined frequency, and outputs the converted operation clock signal to the content generation part  240 , the signal processing part  250 , the reproduction apparatus data input/output part  280 , and the like. 
     Further, the reproduction apparatus operation clock conversion part  230  includes a first frequency conversion part (not shown), a second frequency conversion part (not shown), and a signal switching part (not shown). The first frequency conversion part is a frequency converter which is high in input frequency gain and compatible with a signal large in frequency variation. The second frequency conversion part is a frequency converter which is low in input frequency gain and compatible with a signal relatively small in frequency variation, and can convert the signal into an operation clock signal having a frequency small in error with respect to a predetermined frequency. The signal switching part switches between the reference operation clock signal input from the reproduction apparatus reference operation clock generation part  210  to the reproduction apparatus operation clock conversion part  230  and the received operation clock signal input from the ARC reception part  280   a  to the reproduction apparatus operation clock conversion part  230 , based on control by the reproduction apparatus control part  270  described later. 
     Specifically, the signal switching part switches the input source to any one of the received operation clock signal at 24 MHz generated by and output from the ARC reception part  280   a  when receiving the clock at 48 KHz and the reference operation clock signal at 24 MHz generated by the reproduction apparatus reference operation clock generation part  210  based on the control by the reproduction apparatus control part  270  in the reproduction apparatus operation clock conversion part  230 . The first frequency conversion part converts the input operation clock signal at 24 MHz into the operation clock signal at 13.5 MHz, and outputs the operation clock signal at 13.5 MHz to the second frequency conversion part. The second frequency conversion part further converts the operation clock signal at 13.5 MHz into an operation clock signal at 27 MHz, and outputs the operation clock signal to the content generation part  240 , the reproduction apparatus signal processing part  250 , the reproduction apparatus data input/output part  280 , and the like. Note that, the first frequency conversion part may convert the input operation clock signal at 24 MHz into an operation clock signal at 27 MHz, and may output the operation clock signal at 27 MHz to the second frequency conversion part, and the second frequency conversion part may further convert the operation clock at 27 MHz into the operation clock signal at 27 MHz. 
     The content generation part  240  reads content data recorded on a disc, or content data stored in a semiconductor memory, and outputs the content data to the reproduction apparatus signal processing part  250 . Moreover, the content generation part  240  includes a network connection part (not shown), acquires the content data by downloading the content data stored in a server or the like via a network, or receiving a stream of the content data, and outputs the content data to the reproduction apparatus signal processing part  250 . 
     The reproduction apparatus signal processing part  250  applies various signal processing such as decode processing to the content data generated by the content generation part  240 . For example, the reproduction apparatus signal processing part  250  applies the decode processing to the audio data and the video data, multi-channel processing to the audio data, and processing such as 3D conversion to the video data. 
     The reproduction apparatus data input/output part  280  converts the content data output from the reproduction apparatus signal processing part  250  into data in a data format which can be transmitted on the multimedia data transmission cable  400  connected between the content reproduction apparatus  201  and the content output apparatus  301 , and outputs the converted content data in order to transmit the content data from the content reproduction apparatus  201  to the content output apparatus  301 . In this embodiment, the content reproduction apparatus  201  and the content output apparatus  301  are connected to each other via the HDMI cable  400 , which serves as a multimedia data transmission cable. The reproduction apparatus data input/output part  280  has an HDMI interface function, and converts data into data that matches the data transmission over the HDMI interface to transmit the content data via the HDMI cable  400  to the content output apparatus  301 . 
     The reproduction apparatus data input/output part  280  includes the ARC reception part  280   a . The ARC reception part  280   a  receives the operation clock signal transmitted from an ARC transmission part  380   a , which is described later, of the output apparatus data input/output part  380  of the content output apparatus  301  via the HDMI cable  400 , converts the frequency of the received operation clock signal into a predetermined frequency by means of an integrated frequency converter (not shown), and outputs the operation clock signal (received operation clock signal) to which the frequency conversion has been applied to the reproduction apparatus operation clock conversion part  230 . Specifically, the ARC reception part  280   a  receives the operation clock signal at 48 kHz from the content output apparatus  301 , converts the operation clock signal into the operation clock signal at 24 MHz by means of the integrated frequency converter, and outputs the operation clock signal at 24 MHz to the reproduction apparatus operation clock conversion part  230 . 
     The operation clock signal at 24 MHz input from the ARC reception part  280   a  is the received operation clock signal generated based on the operation clock signal at 48 kHz transmitted via the HDMI cable  400 , and is a signal large in frequency variation with respect to the reference frequency. Therefore, the first frequency conversion part high in input frequency gain converts the operation clock signal into the operation clock signal narrow in frequency variation range with respect to the frequency serving as the reference. In other words, the operation clock signal at 24 MHz is converted into the operation clock signal having a frequency range of 13.5 MHz±5%. Then, the operation clock signal in the frequency range of 13.5 MHz±5% output from the first frequency conversion part is converted into the operation clock signal narrower in frequency variation range with respect to the predetermined frequency and high in precision by the second frequency conversion part low in the input frequency gain. In other words, the operation clock signal in the frequency range of 13.5 MHz±5% is converted into the operation clock signal in a frequency range of 27 kHz±0.5%, and the operation clock signal is output to the content generation part  240 , the reproduction apparatus signal processing part  250 , the reproduction apparatus data input/output part  280 , and the like. The content generation part  240 , the reproduction apparatus signal processing part  250 , the reproduction apparatus data input/output part  280 , and the like operate in synchronization with the operation clock signal small in error with respect to the predetermined frequency. Therefore, the content generation part  240 , the reproduction apparatus signal processing part  250 , the reproduction apparatus data input/output part  280 , and the like operate without a loss in synchronization and the like. 
     The reproduction apparatus control part  270  controls the overall content reproduction apparatus  201 . The reproduction apparatus control part  270  provides control to convert the frequency of the operation clock signal in the reproduction apparatus operation clock conversion part  230  based on the operation clock signal received from the content output apparatus  301 , thereby operating the content generation part  240 , the reproduction apparatus signal processing part  250 , the reproduction apparatus data input/output part  280 , and the like based on the operation clock signal, and transmitting the content data to the content output apparatus  301 . 
     Further, the reproduction apparatus control part  270  detects whether the operation clock signal can be received from the content output apparatus  301  based on turning on/off of the power supply, setting by the user, the connection of the HDMI cable  400 , and the like, and if the operation clock signal can be received from the content output apparatus  301 , controls the signal switching part of the reproduction apparatus operation clock conversion part  230  to generate the operation clock signal based on the received operation clock signal received by the ARC reception part  280   a , thereby controlling the respective parts in the apparatus to operate. Moreover, the reproduction apparatus control part  270  detects whether the operation clock signal can be received from the content output apparatus  301 , and if the reproduction apparatus control part  270  detects that the operation clock signal cannot be received from the content output apparatus  301 , controls the signal switching part of the reproduction apparatus operation clock conversion part  230  to generate the operation clock signal based on the reference operation clock signal output by the reproduction apparatus reference operation clock generation part  210 , thereby controlling the respective parts in the apparatus to operate. 
     Next, the content output apparatus  301  includes an output apparatus data input/output part  380 , an ARC transmission part  380   a  an output apparatus signal processing part  320 , an output part  330 , an output apparatus reference operation clock generation part  340 , and an output apparatus control part  360 . 
     The output apparatus data input/output part  380  receives the content data transmitted via the HDMI cable  400  from the content reproduction apparatus  201 . The output apparatus data input/output part  380  outputs the received content data to the output apparatus signal processing part  320 . 
     The output apparatus signal processing part  320  applies signal processing to the content data input by the output apparatus data input/output part  380  into the content output apparatus  301 , and outputs the processed content data to the output part  330 . On this occasion, the signal processing applied to the content data includes, for example, the surround conversion processing applied to the audio data, and the superimposing processing for the on-screen display (OSD) signal applied to the video data. 
     The output part  330  includes an amplification part (not shown) for amplifying the audio data, and a video encoder (not shown) for converting the video data into a video signal format for displaying the video data on a television set or a monitor. The output part  330  separates the content data to which the signal processing has been applied by the output apparatus signal processing part  320  into the video data and the audio data, and outputs the video data and the audio data to an outside of the content output apparatus  301 . The audio data is output via the amplification part to speakers or the like connected to output terminals with a connection cable or the like. The video data is output via the video encoder to a television set or a monitor connected to output terminals with a connection cable or the like. 
     The output apparatus reference operation clock generation part  340  includes a crystal oscillator (not shown), and generates the reference operation clock signal. In this embodiment, the reference operation clock signal serves as a reference for the operation clock signal of the content output apparatus  301 , and as a reference for the operation clock signal to be transmitted to the content reproduction apparatus  201 . Specifically, the output apparatus reference operation clock generation part  340  generates a reference operation clock signal at 24 MHz, and outputs the reference operation clock signal to the output apparatus data input/output part  380 , the output apparatus signal processing part  320 , the output part  330 , and the like. 
     The ARC transmission part  380   a  converts the frequency of the reference operation clock signal generated by the output apparatus reference operation clock generation part  340  into the predetermined frequency, then converts the reference operation clock signal into the reference operation clock signal in the SPDIF format, and transmits the operation clock signal via the data transmission line of the HDMI cable  400  to the content reproduction apparatus  201 . In this embodiment, the reference operation clock signal at 24 MHz generated by the output apparatus reference operation clock generation part  340  is converted into the operation clock signal having a frequency of 48 kHz, and the operation clock signal is transmitted via the data transmission line of the HDMI cable  400  to the content reproduction apparatus  201 . 
     The output apparatus control part  360  controls the overall content output apparatus  301 . The output apparatus control part  360  provides the control of converting the reference operation clock signal generated by the output apparatus reference operation clock generation part  340  into the reference operation clock signal in the SPDIF format and transmitting the reference operation clock signal from the ARC transmission part  380   a  via the HDMI cable  400  to the content reproduction apparatus  201 , and the control of receiving the content data transmitted from the content reproduction apparatus  201 , applying the signal processing to the content data, and then, outputting the content data from the output part  330  to the outside. 
     A description is now given of processing of transmitting the content data between the content reproduction apparatus  201  and the content output apparatus  301 . 
       FIG. 5  is a flowchart illustrating the processing relating to the content data transmission in the content data transmission system according to the second embodiment of the present invention. 
     As described in the first embodiment, when the mode check processing illustrated in  FIG. 2  is finished, the content reproduction apparatus  201  and the content output apparatus  301  are set to such a state that the content reproduction apparatus  201  and the content output apparatus  301  can operate in the output apparatus clock operation mode (S 1 ). When the content output apparatus  301  becomes operable in the output apparatus clock operation mode, the content output apparatus  301  transmits such a notification that the operation clock signal is transmitted via the HDMI cable  400  to the content reproduction apparatus  201 , and the ARC transmission part  380   a  starts the transmission of the operation clock signal to the ARC reception part  280   a  via the HDMI cable  400  (S 2 ). 
     Specifically, in the content output apparatus  301 , the switch of the mode causes the ARC transmission part  380   a  to generate the operation clock signal at 48 kHz based on the reference operation clock signal generated by the output apparatus reference operation clock generation part  340 , and to start the transmission of the operation clock via the HDMI cable  400  to the content reproduction apparatus  201 . 
     The reproduction apparatus control part  270  of the content reproduction apparatus  201  checks whether the ARC reception part  280   a  has received the operation clock signal at 48 kHz from the content output apparatus  301  or not (S 3 ), and when the ARC reception part  280   a  receives the operation clock signal (YES in S 3 ), the ARC reception part  280   a  generates the operation clock signal at 24 MHz based on the received operation clock signal, and outputs the generated operation clock signal to the reproduction apparatus operation clock conversion part  230  (S 4 ). Regarding the reception of the operation clock signal (S 3 ), if the operation clock signal can be received within a predetermined elapsed time (NO in S 3 , and NO in S 12 ) (YES in S 3 ), the content reproduction apparatus  201  generates the received operation clock signal based on the received operation clock signal, and outputs the received operation clock signal to the reproduction apparatus operation clock conversion part  230  (S 4 ). 
     The reproduction apparatus clock conversion part  230  generates the synchronized operation clock signal (reproduction apparatus operation clock signal) at 27 MHz based on the received operation clock signal at 24 MHz, and outputs the operation clock signal to the content generation part  240 , the reproduction apparatus signal processing part  250 , and the reproduction apparatus data input/output part  280  (S 5 ). 
     On this occasion (S 3 ), if the ARC reception part  280   a  cannot receive the operation clock signal from the content output apparatus  301  within a predetermined period due to a defect of the HDMI cable  400  or the like after the operation in the output apparatus clock operation mode starts (NO in S 3 , YES in S 12 ), the reproduction apparatus control part  270  switches the output apparatus clock operation mode, and provides such control that the reproduction apparatus operation clock signal is generated based on the reference operation clock signal generated by the reproduction apparatus reference operation clock generation part  210  (S 13 ) to operate the apparatus. The predetermined period in S 12  is, for example, approximately five seconds. 
     If the content reproduction apparatus  201  cannot receive the operation clock signal within the predetermined period from the content output apparatus  301 , the reproduction apparatus control part  270  controls the content reproduction apparatus  201  to operate based on the reproduction apparatus operation clock signal generated based on the reference operation clock signal in the content reproduction apparatus  201 , and thus such a case that the content data is not output from the content reproduction apparatus  201  for a long period is prevented from occurring. As a result, even if a transmission error of the operation clock signal occurs between the content reproduction apparatus  201  and the content output apparatus  301 , the user does not need to carry out a complex change in setting, and can listen to or view the content via the content output apparatus  301 . 
     Moreover, if the setting is switched from the output apparatus clock operation mode due to the transmission error of the operation clock signal as described above, the reproduction apparatus control part  270  presents such a notification that the mode setting has been changed on a display part (not shown) of the content reproduction apparatus  201 , thereby notifying the user of the change. As a result of the display and notification, the user can recognize that the operation is not carried out in the output apparatus clock operation mode. Moreover, if such a defect that the HDMI cable  400  is disconnected occurs, or a connection failure of the HDMI cable  400  occurs, the user can recognize the situation. 
     The content generation part  240  operates based on the operation clock signal supplied from the reproduction apparatus operation clock conversion part  230 , reads content data from a mounted disc or downloads content data via the network, and outputs the content data to the reproduction apparatus signal processing part  250  (S 6 ). 
     The reproduction apparatus signal processing part  250  also operates based on the operation clock signal supplied from the reproduction apparatus operation clock conversion part  230 , applies predetermined signal processing to the content data input from the content generation part  240 , and outputs the content data to the reproduction apparatus data input/output part  280  (S 7 ). 
     The reproduction apparatus data input/output part  280  also operates based on the operation clock signal supplied from the reproduction apparatus operation clock conversion part  230 , converts the content data input from the reproduction apparatus signal processing part  250  into content data in a predetermined signal format, and transmits the content data via the HDMI cable  400  to the content output apparatus  301  (S 8 ). 
     The output apparatus data input/output part  380  receives the content data output from the content reproduction apparatus  201  (S 9 ), converts the signal format into a predetermined format, and outputs the content data to the output apparatus signal processing part  320  in the content output apparatus  301  (Step  10 ). The respective parts of the content output apparatus  301  (in  FIG. 4 , the output apparatus data input/output part  380 , the output apparatus signal processing part  320 , and the output part  330 ) operate based on the operation clock signal generated by the output apparatus reference operation clock generation part  340 . 
     The output apparatus signal processing part  320  applies predetermined signal processing to the content data output from the output apparatus data input/output part  380 , and outputs the processed content data to the output part  330  (S 10 ). The output part  330  applies signal processing, specifically, amplifies the audio data, applies video encoding processing to the video data, and then outputs the audio data and the video data as the video signal and the audio signal, respectively, to the external apparatus (S 11 ). 
     A description has been given of the content data transmission system  101  according to this embodiment configured so that the mode check processing is carried out in order to check whether the content reproduction apparatus  201  and the content output apparatus  301  are each compatible with the output apparatus clock operation mode or not, but the content data transmission system  101  may be configured so that the mode check processing is not carried out, data representing that the operation clock signal is output from the content output apparatus  301  is superimposed on the operation clock signal in order to check the reliability of the clock signal input to the reproduction apparatus data input/output part  280 , and only if the operation clock signal received on the content reproduction apparatus  201  side is superimposed with the data representing that the operation clock signal is output from the content output apparatus  301 , the content data transmission system  101  operates in the output apparatus clock operation mode. For example, if The output apparatus data input/output part  380  transmits the operation clock to the reproduction apparatus data input/output part  280 , the output apparatus control part  360  may control the ARC transmission part  380   a  so as to transmit the operation clock signal superimposed with a predetermined bi-phase signal. The reproduction apparatus control part  270  may determine whether the predetermined bi-phase signal is superimposed on the operation clock received by the reproduction apparatus data input/output part  280 . If the bi-phase signal is superimposed, the reproduction apparatus control part  270  may provide control so as to operate in the output apparatus clock operation mode, and if the bi-phase signal is not superimposed, may switch the signal switching part of the reproduction apparatus operation clock conversion part  230  to generate the reproduction apparatus operation clock signal based on the reference operation clock signal generated by the reproduction apparatus reference operation clock generation part  210 , and may provide control so as to operate based on the reproduction apparatus operation clock signal. As a result, a circuit configuration required for the mode check processing can be omitted, and a time required for the mode check processing can be reduced. Moreover, even if an operation clock signal transmitted from an apparatus other than the content output apparatus  301  is received by any chance while the HDMI cable  400  is connected to the apparatus other than the content output apparatus  301 , a jitter can be prevented from being generated on the audio data to be reproduced, and the sound quality and the image quality can be prevented from degrading. 
     In the content data transmission system  101  according to this embodiment, the ARC transmission part  380   a  transmits the operation clock signal at 48 kHz to the ARC reception part  280   a , the operation clock signal at 27 MHz is generated from the operation clock signal at 48 kHz, the operation clock signal at 24 MHz, which is the operation clock signal for the 48 kHz system, and an operation clock signal at 22 MHz, which is the operation clock signal for a 44.1 kHz system, are generated from the operation clock signal at 27 MHz, but the content data transmission system  101  may be configured, for example, to switch and transmit the plurality of clock signals. For example, the ARC transmission part  380   a  is configured so as to switch and transmit the operation clock signal at 48 kHz and the operation clock signal at 44.1 kHz, and the ARC reception part  280   a  is configured to operate based on the received operation clock frequency. As a result, for example, when content data including video data recorded on a recording medium such as a DVD and a BD is reproduced, the switching can be made so as to operate based on the operation clock signal at 48 kHz, and when content data not including video data recorded on a recording medium such as a CD is reproduced, the switching can be made so as to operate based on the operation clock signal at 44.1 kHz, and hence an arbitrary operation clock is selected for operation out of the plurality of the operation clocks depending on content data to be reproduced. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to the content data transmission system including the content reproduction apparatus for reproducing the content data, and the content output apparatus for applying the signal processing and the amplification to the content data and outputting the content data. 
     REFERENCE SIGNS LIST 
     
         
         
           
               100  . . . content data transmission system 
               200  . . . content reproduction apparatus,  210  . . . reproduction apparatus reference operation clock generation part,  220  . . . operation clock reception part,  230  . . . reproduction apparatus operation clock conversion part,  240  . . . content generation part,  250  . . . reproduction apparatus signal processing part,  260  . . . data output part 
               300  . . . content output apparatus,  310  . . . data input part,  320  . . . output apparatus signal processing part,  330  . . . output part,  340  . . . output apparatus reference operation clock generation part,  350  . . . operation clock transmission part,  360  . . . output apparatus control part 
               400  . . . multimedia data transmission cable 
               500  . . . operation clock transmission cable 
               101  . . . content data transmission system 
               201  . . . content reproduction apparatus 
               280  . . . reproduction apparatus data input/output part,  280   a  . . . ARC reception part 
               301  . . . content output apparatus 
               380  . . . output apparatus data input/output part,  380   a  . . . ARC transmission part