Abstract:
A conventional audio/video transmission system including an audio/video transmitter apparatus and an audio/video receiver apparatus suffers from delay of video relative to audio resulting from reproducing audio from the audio signal output from the audio/video transmitter apparatus and reproducing video from the video signal output from the audio/video receiver apparatus. To solve this inconvenience, according to the invention, in an audio/video transmission system including an audio/video transmitter apparatus and an audio/video receiver apparatus, the audio/video transmitter apparatus additionally has an audio delay circuit that outputs the input analog audio signal with a predetermined delay time.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an audio/video transmission system for transmitting audio and video signals on a wireless basis.  
           [0003]    2. Description of the Prior Art  
           [0004]    [0004]FIG. 8 shows an example of the configuration of a conventional audio/video transmission system for transmitting audio and video signals on a wireless basis. The audio/video transmission system shown in FIG. 8 includes an audio/video transmitter apparatus  100  and an audio/video receiver apparatus  200 .  
           [0005]    First, the circuit configuration of the audio/video transmitter apparatus  100  will be described. The audio/video transmitter apparatus  100  includes a video input terminal  1 , an audio input terminal  2 , an audio output terminal  3 , a video A/D converter circuit  4 , a data compression circuit  5 , a wireless transmitter circuit  6 , an antenna terminal  7 , an audio A/D converter circuit  9 , and a power supply circuit  10 .  
           [0006]    The video input terminal  1  is connected to the input end of the video A/D converter circuit  4 . The output end of the video A/D converter circuit  4  is connected to one input end of the data compression circuit  5 . The audio input terminal  2  is connected to the input end of the audio A/D converter circuit  9  and to the audio output terminal  3 . The output end of the audio A/D converter circuit  9  is connected to the other input end of the data compression circuit  5 . The output end of the data compression circuit  5  is connected to the input end of the wireless transmitter circuit  6 , and the output end of the wireless transmitter circuit  6  is connected to the antenna terminal  7 . The power supply circuit  10  is connected to each of the video A/D converter circuit  4 , data compression circuit  5 , wireless transmitter circuit  6 , and audio A/D converter circuit  9 . Moreover, an antenna  8  is externally fitted to the audio/video transmitter apparatus  100 . Specifically, the antenna  8  is connected to the antenna terminal  7 .  
           [0007]    Next, the circuit configuration of the audio/video receiver apparatus  200  will be described. The audio/video receiver apparatus  200  includes an antenna terminal  22 , a wireless receiver circuit  23 , a data decompression circuit  24 , a video D/A converter circuit  25 , a video output terminal  26 , an audio D/A converter circuit  27 , an audio output terminal  28 , and a power supply circuit  29 .  
           [0008]    The antenna terminal  22  is connected to the input end of the wireless receiver circuit  23 . The output end of the wireless receiver circuit  23  is connected to the input end of the data decompression circuit  24 . One output end of the data decompression circuit  24  is connected to the input end of the video D/A converter circuit  25 , and the other output end of the data decompression circuit  24  is connected to the input end of the audio D/A converter circuit  27 . The output end of the video D/A converter circuit  25  is connected to the video output terminal  26 , and the output end of the audio D/A converter circuit  27  is connected to the audio output terminal  28 . The power supply circuit  29  is connected to each of the wireless receiver circuit  23 , data decompression circuit  24 , video D/A converter circuit  25 , and audio D/A converter circuit  27 . Moreover, an antenna  21  is externally fitted to the audio/video receiver apparatus  200 . Specifically, the antenna  21  is connected to the antenna terminal  22 .  
           [0009]    Next, the operation of the audio/video transmission system shown in FIG. 8 will be described. First, the operation of the audio/video transmitter apparatus  100  will be described. An alternating-current voltage fed from outside is converted by the power supply circuit  10  into a predetermined direct-current voltage (+B), which is fed to each of the video A/D converter circuit  4 , data compression circuit  5 , wireless transmitter circuit  6 , and audio A/D converter circuit  9 .  
           [0010]    The video input terminal  1  and audio input terminal  2  are connected to a video playback apparatus such as a videocassette recorder (not illustrated). An analog video signal A V1  from the video playback apparatus is fed in via the video input terminal  1 , and is converted into a digital video signal D V1  by the video A/D converter circuit  4 .  
           [0011]    On the other hand, an analog audio signal A A1  from the video playback apparatus is fed in via the audio input terminal  2 , and is split into two signals, of which one is converted into a digital audio signal D A1  by the audio A/D converter circuit  9 , and of which the other is directly fed out via the audio output terminal  3 .  
           [0012]    The digital video signal D V1  and digital audio signal D A1  are subjected to data compression performed by the data compression circuit  5 , and are thereby converted into a compressed audio/video signal C AV1 . The compressed audio/video signal C AV1  is modulated into a radio-frequency signal (having 2.4 GHz, for example) by the wireless transmitter circuit  6 , and is then transmitted in the form of a radio wave from the antenna  8 .  
           [0013]    Next, the operation of the audio/video receiver apparatus  200  will be described. An alternating-current voltage fed from outside is converted by the power supply circuit  29  into a predetermined direct-current voltage (+B), which is fed to each of the wireless receiver circuit  23 , data decompression circuit  24 , video D/A converter circuit  25 , and audio D/A converter circuit  27 .  
           [0014]    The radio wave transmitted from the antenna  8  is received by the antenna  21 , and the thus received radio-frequency signal is demodulated by the wireless receiver circuit  23  into a compressed audio/video signal C AV2 , which is identical with the compressed audio/video signal C AV1 . The compressed audio/video signal C AV2  is decompressed by the data decompression circuit  24 , and is thereby converted into a digital video signal D V2  and a digital audio signal D A2 , which are identical with the digital video signal D V1  and digital audio signal D A1 , respectively.  
           [0015]    The digital video signal D V2  is converted by the video D/A converter circuit  25  into an analog video signal A V2 , which is identical with the analog video signal A V1 , and is then fed out via the video output terminal  26 . The digital audio signal D A2  is converted by the audio D/A converter circuit  27  into an analog audio signal A A2 , which is identical with the analog audio signal A A1 , and is then fed out via the audio output terminal  28 .  
           [0016]    By connecting the video output terminal  26  and audio output terminal  28  to the external input terminals of, for example, a television monitor (not illustrated), it is possible to view, on the television monitor that is connected to the audio/video receiver apparatus  200 , the audio and video reproduced on the video playback apparatus, such as a videocassette recorder, that is connected to the audio/video transmitter apparatus  100 .  
           [0017]    Inconveniently, however, the audio/video transmission system shown in FIG. 8 has the following disadvantage. When the audio/video transmission system is used in such a way that video is reproduced from the analog video signal fed out via the video output terminal  26  and that audio is reproduced from the analog audio signal fed out via the audio output terminal  3 , while the analog video signal fed out via the video output terminal  26  is subjected to data compression and then to data decompression before it reaches the video output terminal  26 , the analog audio signal fed out via the audio output terminal  3  is not subjected to either data compression or data decompression before it reaches the audio output terminal  3 . Thus, the analog video signal fed out via the video output terminal  26  is delayed by the time required to perform signal processing for data compression and data decompression relative to the analog audio signal fed out via the audio output terminal  3 . That is, video is delayed relative to audio. For example, in a case where the data compression performed by the data compression circuit  5  and the data decompression performed by the data decompression circuit  24  are performed by methods complying with MPEG2, video is delayed by about one second relative to audio.  
           [0018]    The audio/video transmission system is used in the fashion described above, for example, in a case where a liquid crystal video projector and a screen on which to project an optical image from the liquid crystal video projector are arranged so as to face each other. In this case, the audio/video transmitter apparatus  100  is placed, along with an amplifier and speakers, near the screen, and the audio/video receiver apparatus  200  is placed near the liquid crystal video projector. Then, the speakers are connected via the amplifier to the audio output terminal  3  of the audio/video transmitter apparatus  100 , and the external input terminal of the liquid crystal video projector is connected to the video output terminal  26  of the audio/video receiver apparatus  200 .  
         SUMMARY OF THE INVENTION  
         [0019]    An object of the present invention is to provide an audio/video transmission system including an audio/video transmitter apparatus and an audio/video receiver apparatus which is free from delay of video relative to audio even in a case where audio is reproduced from the audio signal output from the audio/video transmitter apparatus and video is reproduced from the video signal output from the audio/video receiver apparatus.  
           [0020]    To achieve the above object, according to the present invention, an audio/video transmission system is provided with:  
           [0021]    an audio/video transmitter apparatus;  
           [0022]    a wireless signal transmitter for transmitting a wireless signal according to the signal output from a wireless transmitter circuit provided in the audio/video transmitter apparatus;  
           [0023]    a wireless signal receiver for receiving the wireless signal transmitted from the wireless signal transmitter to output a signal according to the received wireless signal;  
           [0024]    and an audio/video receiver apparatus including:  
           [0025]    a wireless receiver circuit for demodulating the signal output from the wireless signal receiver to output a compressed audio/video signal; and  
           [0026]    a data decompression circuit for performing data decompression on the compressed audio/video signal output from the wireless receiver circuit.  
           [0027]    Here, the audio/video transmitter apparatus comprises:  
           [0028]    a video A/D converter circuit for converting an input analog video signal into a digital video signal;  
           [0029]    an audio A/D converter circuit for converting an input analog audio signal into a digital audio signal;  
           [0030]    a data compression circuit for performing data compression on the digital video and audio signals;  
           [0031]    a wireless transmitter circuit for modulating the compressed audio/video signal output from the data compression circuit; and  
           [0032]    an audio delay circuit for outputting the input analog audio signal with a predetermined delay time. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]    This and other objects and features of the present invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanying drawings in which:  
         [0034]    [0034]FIG. 1 is a diagram showing the configuration of the audio/video transmission system of a first embodiment of the invention;  
         [0035]    [0035]FIG. 2 is a diagram showing the configuration of the audio/video transmitter apparatus provided in the audio/video transmission system of a second embodiment of the invention;  
         [0036]    [0036]FIG. 3 is a flow chart showing the operation of the control circuit provided in the audio/video transmitter apparatus shown in FIG. 2;  
         [0037]    [0037]FIG. 4 is a diagram showing the configuration of the audio/video transmitter apparatus provided in the audio/video transmission system of a third embodiment of the invention;  
         [0038]    [0038]FIG. 5 is a flow chart showing the operation of the control circuit provided in the audio/video transmitter apparatus shown in FIG. 4;  
         [0039]    [0039]FIG. 6 is a diagram showing the configuration of the audio/video transmitter apparatus provided in the audio/video transmission system of a fourth embodiment of the invention;  
         [0040]    [0040]FIG. 7 is a flow chart showing the operation of the control circuit provided in the audio/video transmitter apparatus shown in FIG. 6; and  
         [0041]    [0041]FIG. 8 is a diagram showing an example of the configuration of a conventional audio/video transmission system. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]    [0042]FIG. 1 shows the configuration of the audio/video transmission system of a first embodiment of the invention. In FIG. 1, such circuit blocks as are found also in FIG. 8 are identified with the same reference numerals, and their explanations will not be repeated.  
         [0043]    The audio/video transmission system shown in FIG. 1 includes an audio/video transmitter apparatus  101 , an antenna  8 , an audio/video receiver apparatus  200 , and an antenna  21 .  
         [0044]    As compared with the audio/video transmitter apparatus  100  provided in the audio/video transmission system shown in FIG. 8, the audio/video transmitter apparatus  101  is additionally provided with an audio delay circuit  11 . The audio delay circuit  11  is composed of an A/D converter circuit  12 , a delay circuit  13 , and a D/A converter circuit  14 .  
         [0045]    The audio input terminal  2  is connected to the input end of the audio A/D converter circuit  9  and to the input end of the A/D converter circuit  12 . The output end of the A/D converter circuit  12  is connected to the input end of the delay circuit  13 , and the output end of the delay circuit  13  is connected to the input end of the D/A converter circuit  14 . The output end of the D/A converter circuit  14  is connected to the audio output terminal  3 .  
         [0046]    In this configuration, an analog audio signal A A1  fed in via the audio input terminal  2  is split into two signals, of which one is converted by the audio A/D converter circuit  9  into a digital audio signal D A1 , and of which the other is converted by the A/D converter circuit  12  into a digital audio signal. The digital audio signal output from the A/D converter circuit  12  is given a predetermined delay time by the delay circuit  13 , and is then converted by the D/A converter circuit  14  into an analog audio signal, which is then fed out via the audio output terminal  3 . The predetermined delay time produced by the delay circuit  13  is so determined as to be substantially equal to the time required for the signal processing performed by the data compression circuit  5  and data decompression circuit  24 . For example, in a case where the data compression performed by the data compression circuit  5  and the data decompression performed by the data decompression circuit  24  are performed by methods complying with MPEG2, the time required for the signal processing performed by the data compression circuit  5  and data decompression circuit  24  is about one second, and accordingly it is advisable that the predetermined delay time produced by the delay circuit  13  be set to be about one second.  
         [0047]    When the audio/video transmission system shown in FIG. 1 is used in such a way that video is reproduced from the analog video signal A V2  fed out via the video output terminal  26  and that audio is reproduced from the analog audio signal fed out via the audio output terminal  3 , the analog video signal A V2  fed out via the video output terminal  26  is subjected to data compression and then to data decompression and accordingly takes extra time before it reaches the video output terminal  26 , and the analog audio signal fed out via the audio output terminal  3  is given a delay time equal to the time required to perform signal processing for data compression and data decompression before it reaches the audio output terminal  3 . This makes it possible to substantially eliminate the time difference between the analog video signal A V2  fed out via the video output terminal  26  and the analog audio signal fed out via the audio output terminal  3 . In this way, it is possible to realize an audio/video transmission system that is free from delay of video relative to audio even in a case where audio is reproduced from the audio signal output from an audio/video transmitter apparatus and video is reproduced from the video signal output from an audio/video receiver apparatus.  
         [0048]    Here, a single A/D converter circuit may be shared as the audio A/D converter circuit  9  and A/D converter circuit  12 . In that case, the output signal of the shared circuit is split into two signals, which are then fed to the data compression circuit  5  and delay circuit  13 , respectively.  
         [0049]    Next, the audio/video transmission system of a second embodiment of the invention will be described. The audio/video transmission system of the second embodiment includes an audio/video transmitter apparatus  102  as shown in FIG. 2, an antenna  8  as shown in FIG. 2, the same audio/video receiver apparatus as that provided in the audio/video transmission system of the first embodiment, and the antenna connected to that audio/video receiver apparatus. In FIG. 2, such circuit blocks as are found also in FIG. 1 are identified with the same reference numerals, and their explanations will not be repeated.  
         [0050]    As compared with the audio/video transmitter apparatus  101  provided in the audio/video transmission system shown FIG. 1, the audio/video transmitter apparatus  102  is additionally provided with a control signal input terminal  15 , a control circuit  16 , and a switcher circuit  17 .  
         [0051]    The control signal input terminal  15  is connected to the input end of the control circuit  16 , and the output end of the control circuit  16  is connected to the control terminal of the switcher circuit  17 .  
         [0052]    The audio input terminal  2  is connected to the movable contact of the switcher circuit  17 . One fixed contact of the switcher circuit  17  is connected to the input end of the audio A/D converter circuit  9 , and the other fixed contact of the switcher circuit  17  is connected to the input end of the A/D converter circuit  12 .  
         [0053]    The control circuit  16  controls the switcher circuit  17  according to a control signal (hereinafter referred to as the external control signal) fed in via the control signal input terminal  15 . According to the output signal of the control circuit  16 , the switcher circuit  17  switches whether to feed the analog audio signal A A1  fed in via the audio input terminal  2  to the audio A/D converter circuit  9  or to the A/D converter circuit  12 .  
         [0054]    [0054]FIG. 3 is a flow chart showing the operation of the control circuit  16  when it is realized with a microcomputer. In this embodiment, it is assumed that the external control signal is either logically high or low at a time.  
         [0055]    First, the control circuit  16  checks whether the external control signal is high or not (step S 1 ). If the external control signal is high (“Yes” in step S 1 ), the flow proceeds to step S 2 . By contrast, if the external control signal is not high but low (“No” in step S 1 ), the flow proceeds to step S 3 .  
         [0056]    In step S 2 , the control circuit  16  controls the switcher circuit  17  so that the switcher circuit  17  feeds the analog audio signal A A1  fed in via the audio input terminal  2  to the audio A/D converter circuit  9 . The flow then returns to step S 1 .  
         [0057]    In step S 3 , the control circuit  16  controls the switcher circuit  17  so that the switcher circuit  17  feeds the analog audio signal A A1  fed in via the audio input terminal  2  to the A/D converter circuit  12  provided in the audio delay circuit  11 . The flow then returns to step S 1 .  
         [0058]    It should be understood that the external control signal described above as being either logically high or low at a time is merely an example of an external control signal usable as such, and that the present invention may be practiced in any other manner than specifically described above.  
         [0059]    The audio/video transmission system of the second embodiment has, in addition to the advantages offered by the audio/video transmission system of the first embodiment described earlier, the following advantage. For example, in a case where speakers are connected via an amplifier to the audio output terminal  3  of the audio/video transmitter apparatus  102  and the external input terminals of a television monitor are connected to the video and audio output terminals of the audio/video receiver apparatus, the user, by controlling the control signal fed in via the control signal input terminal  15 , can select either the speakers or television monitor as the device by which to output audio. This helps prevent the speakers and television monitor from outputting audio simultaneously.  
         [0060]    Here, a single A/D converter circuit may be shared as the audio A/D converter circuit  9  and A/D converter circuit  12 . In that case, the audio input terminal  2  is connected to the input end of the shared circuit, and the output end of the shared circuit is connected to the movable contact of the switcher circuit  17 . Moreover, one fixed contact of the switcher circuit  17  is connected to the input end of the data compression circuit  5 , and the other fixed contact of the switcher circuit  17  is connected to the input end of the delay circuit  13 . Thus, according to the output signal of the control circuit  16 , the switcher circuit  17  switches whether to feed the output signal of the shared circuit to the data compression circuit  5  or to the delay circuit  13 .  
         [0061]    Next, the audio/video transmission system of a third embodiment of the invention will be described. The audio/video transmission system of the third embodiment includes an audio/video transmitter apparatus  103  as shown in FIG. 4, an antenna  8  as shown in FIG. 4, the same audio/video receiver apparatus as that provided in the audio/video transmission system of the first embodiment, and the antenna connected to that audio/video receiver apparatus. In FIG. 4, such circuit blocks as are found also in FIG. 2 are identified with the same reference numerals, and their explanations will not be repeated.  
         [0062]    As compared with the audio/video transmitter apparatus  102  shown in FIG. 2, the audio/video transmitter apparatus  103  lacks the control signal input terminal  15  but is instead additionally provided with a light-receiving circuit  18 , and moreover lacks the control circuit  16  but is instead provided with a control circuit  16 ′ that operates in a different manner than the control circuit  16 . The light-receiving circuit  18  is connected to the input end of the control circuit  16 ′, and the output end of the control circuit  16 ′ is connected to the control terminal of the switcher circuit  17 .  
         [0063]    The light-receiving circuit  18  receives an infrared remote control signal (hereinafter referred to as the remote control signal) transmitted from a remote control transmitter (not illustrated), converts the received remote control signal into an electrical signal, and feeds the electrical signal to the control circuit  16 ′. According to the electrical signal output from the light-receiving circuit  18 , the control circuit  16 ′ controls the switcher circuit  17 .  
         [0064]    [0064]FIG. 5 is a flow chart showing the operation of the control circuit  16 ′ when it is realized with a microcomputer.  
         [0065]    First, on the basis of the electrical signal output from the light-receiving circuit  18 , the control circuit  16 ′ checks whether the remote control signal is a signal requesting “wireless audio signal transmission” or not (step S 11 ). If the remote control signal is a signal requesting “wireless audio signal transmission” (“Yes” in step S 11 ), the flow proceeds to step S 13 . By contrast, if the remote control signal is not a signal requesting “wireless audio signal transmission” (“No” in step S 11 ), the flow proceeds to step S 12 .  
         [0066]    In step S 12 , on the basis of the electrical signal output from the light-receiving circuit  18 , the control circuit  16 ′ checks whether the remote control signal is a signal requesting “wired audio signal transmission” or not (step S 12 ). If the remote control signal is a signal requesting “wired audio signal transmission” (“Yes” in step S 12 ), the flow proceeds to step S 14 . By contrast, if the remote control signal is not a signal requesting “wired audio signal transmission” (“No” in step S 12 ), the flow returns to step S 11 .  
         [0067]    In step S 13 , the control circuit  16 ′ controls the switcher circuit  17  so that the switcher circuit  17  feeds the analog audio signal A A1  fed in via the audio input terminal  2  to the audio A/D converter circuit  9 . The flow then returns to step S 11 .  
         [0068]    In step S 14 , the control circuit  16 ′ controls the switcher circuit  17  so that the switcher circuit  17  feeds the analog audio signal A A1  fed in via the audio input terminal  2  to the A/D converter circuit  12  provided in the audio delay circuit  11 . The flow then returns to step S 11 .  
         [0069]    It should be understood that the remote control signal described above as being a signal requesting “wireless audio signal transmission” at one time and a signal requesting “wired audio signal transmission” at another time is merely an example of a remote control signal usable as such, and that the present invention may be practiced in any other manner than specifically described above.  
         [0070]    The audio/video transmission system of the third embodiment has, in addition to the advantages offered by the audio/video transmission system of the second embodiment described earlier, the following advantage. The user, by using a remote control transmitter, can select the device by which to output audio. This enhances usability.  
         [0071]    Here, a single A/D converter circuit may be shared as the audio A/D converter circuit  9  and A/D converter circuit  12 . In that case, the audio input terminal  2  is connected to the input end of the shared circuit, and the output end of the shared circuit is connected to the movable contact of the switcher circuit  17 . Moreover, one fixed contact of the switcher circuit  17  is connected to the input end of the data compression circuit  5 , and the other fixed contact of the switcher circuit  17  is connected to the input end of the delay circuit  13 . Thus, according to the output signal of the control circuit  16 ′, the switcher circuit  17  switches whether to feed the output signal of the shared circuit to the data compression circuit  5  or to the delay circuit  13 .  
         [0072]    Next, the audio/video transmission system of a fourth embodiment of the invention will be described. The audio/video transmission system of the fourth embodiment includes an audio/video transmitter apparatus  104  as shown in FIG. 6, an antenna  8  as shown in FIG. 6, the same audio/video receiver apparatus as that provided in the audio/video transmission system of the first embodiment, and the antenna connected to that audio/video receiver apparatus. In FIG. 6, such circuit blocks as are found also in FIG. 4 are identified with the same reference numerals, and their explanations will not be repeated.  
         [0073]    As compared with the audio/video transmitter apparatus  103  shown in FIG. 4, the audio/video transmitter apparatus  104  is additionally provided with switch circuits  19  and  20 , and moreover lacks the control circuit  16 ′ but is instead provided with a control circuit  16 ″ that operates in a different manner than the control circuit  16 ′. The light-receiving circuit  18  is connected to the input end of the control circuit  16 ″, and the output end of the control circuit  16 ″ is connected to the control terminal of each of the switcher circuit  17  and switch circuits  19  and  20 . The power supply circuit  10  is connected via the switch circuit  19  to the audio A/D converter circuit  9 , and is connected via the switch circuit  20  to the individual circuits provided in the audio delay circuit  11 . According to the electrical signal output from the light-receiving circuit  18 , the control circuit  16 ″ controls the switcher circuit  17  and switch circuits  19  and  20 .  
         [0074]    [0074]FIG. 7 is a flow chart showing the operation of the control circuit  16 ″ when it is realized with a microcomputer. In FIG. 7, such steps as are found also in FIG. 5 are identified with the same reference symbols.  
         [0075]    First, on the basis of the electrical signal output from the light-receiving circuit  18 , the control circuit  16 ″ checks whether the remote control signal is a signal requesting “wireless audio signal transmission” or not (step S 11 ). If the remote control signal is a signal requesting “wireless audio signal transmission” (“Yes” in step S 11 ), the flow proceeds to step S 13 . By contrast, if the remote control signal is not a signal requesting “wireless audio signal transmission” (“No” in step S 11 ), the flow proceeds to step S 12 .  
         [0076]    In step S 12 , on the basis of the electrical signal output from the light-receiving circuit  18 , the control circuit  16 ″ checks whether the remote control signal is a signal requesting “wired audio signal transmission” or not (step S 12 ). If the remote control signal is a signal requesting “wired audio signal transmission” (“Yes” in step S 12 ), the flow proceeds to step S 14 . By contrast, if the remote control signal is not a signal requesting “wired audio signal transmission” (“No” in step S 12 ), the flow returns to step S 11 .  
         [0077]    In step S 13 , the control circuit  16 ″ controls the switcher circuit  17  so that the switcher circuit  17  feeds the analog audio signal A A1  fed in via the audio input terminal  2  to the audio A/D converter circuit  9 . Thereafter, the control circuit  16 ″ turns the switch circuit  19  on (step S 15 ), and then turns the switch circuit  20  off (step S 17 ). The flow then returns to step S 11 .  
         [0078]    In step S 14 , the control circuit  16 ″ controls the switcher circuit  17  so that the switcher circuit  17  feeds the analog audio signal A A1  fed in via the audio input terminal  2  to the A/D converter circuit  12  provided in the audio delay circuit  11 . Thereafter, the control circuit  16 ″ turns the switch circuit  19  off (step S 16 ), and then turns the switch circuit  20  on (step S 18 ). The flow then returns to step S 11 .  
         [0079]    It should be understood that the remote control signal described above as being a signal requesting “wireless audio signal transmission” at one time and a signal requesting “wired audio signal transmission” at another time is merely an example of a remote control signal usable as such, and that the present invention may be practiced in any other manner than specifically described above.  
         [0080]    The audio/video transmission system of the fourth embodiment has, in addition to the advantages offered by the audio/video transmission system of the third embodiment described earlier, the following advantage. When the analog audio signal A A1  is not fed to the audio A/D converter circuit  9 , the supply of electric power to the audio A/D converter circuit  9  can be turned off Likewise, when the analog audio signal A A1  is not fed to the audio delay circuit  11 , the supply of electric power to the audio delay circuit  11  can be turned off. This makes it possible to reduce to zero the electric power consumed by the audio A/D converter circuit  9  and audio delay circuit  11  when they are in a stand-by state, and thereby save power.  
         [0081]    Here, a single A/D converter circuit may be shared as the audio A/D converter circuit  9  and A/D converter circuit  12 . In that case, the audio input terminal  2  is connected to the input end of the shared circuit, and the output end of the shared circuit is connected to the movable contact of the switcher circuit  17 . Moreover, one fixed contact of the switcher circuit  17  is connected to the input end of the data compression circuit  5 , and the other fixed contact of the switcher circuit  17  is connected to the input end of the delay circuit  13 . Thus, according to the output signal of the control circuit  16 ″, the switcher circuit  17  switches whether to feed the output signal of the shared circuit to the data compression circuit  5  or to the delay circuit  13 . Moreover, the switch circuit  19  is omitted, and the switch circuit  20  turns on and off the supply of electric power to the delay circuit  13  and D/A converter circuit  14 .  
         [0082]    In the first to fourth embodiments described above, an antenna is externally fitted to each of the audio/video transmitter and receiver apparatuses. It is, however, also possible to incorporate the antenna in each of the audio/video transmitter and receiver apparatuses.  
         [0083]    In the first to fourth embodiments described above, the audio/video transmitter and receiver apparatuses achieve wireless communication between them by using a radio wave. It is, however, also possible to use any other wireless signal than a radio wave, for example an infrared signal.  
         [0084]    The audio/video transmitter and receiver apparatuses may be provided with, instead of the power supply circuit that converts an alternating-current voltage into a predetermined direct-current voltage, a DC terminal by way of which a predetermined direct-current voltage is fed in.  
         [0085]    In the second to fourth embodiments described above, the control circuit controls the switcher circuit and/or switch circuits according to a control signal fed from outside. It is, however, also possible to provide the audio/video transmitter apparatus with a detection circuit for detecting whether an external appliance is connected to the audio output terminal  3  or not so that the control circuit controls the switcher circuit and/or switch circuits according to the output signal of the detection circuit.