Digital signal transmission apparatus

Abstract: A digital signal transmission apparatus for transmitting digital video signal and digital audio signal, in which the number of data of an audio synchronizing block containing audio data and synchronizing data is selected equal to the number of data of a video synchronizing block containing video data and synchronizing data, and these data are transmitted on time division basis.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a digital signal transmission apparatus, and more particularly to an apparatus for transmitting digital video signal and digital audio signal. Related Background Art In the field of such transmission apparatus there is known a digital video tape recorder (DVTR) utilizing a magnetic recording-reproducing system as the transmission channel. In the following description such digital video tape recorder will be taken as an example. In the conventional digital video tape recorder, a recording area for the digital video signal (video area) and a recording area for the digital audio signal (audio area) are separately formed on the recording track, and these two signals are recorded and reproduced by separate signal processing circuits. In case of recording audio signal and video signal on a same recording medium, there have generally been conducted separate signal processings for audio and video signals as explained above. For this reason there have been required two series of signal processing circuits, with inevitably increased magnitude of the circuits. Besides, since the amount of audio data is smaller than that of video data, the audio area is designed smaller. Therefore, if the tape is damaged in the longitudinal or transversal direction, the audio data incur severer loss, thus eventually providing sounds of unacceptable quality. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the-drawbacks mentioned above. Another object of the present invention is to provide a digital data transmission apparatus capable of processing audio data and video data in a common manner as far as possible, wherein video blocks are formed in the manner as set out in the appended claims. The above-mentioned objects can be achieved, in an embodiment of the present invention, by an apparatus for transmitting digital video signal and digital audio signal, in which the number of data in an audio synchronizing block containing audio data and synchronizing data is selected equal to that of data in a video synchronizing block containing video data and synchronizing data, and these synchronizing blocks are transmitted in a time division system. Still another object of the present invention is to provide a digital signal transmission apparatus capable of suppressing the deterioration of audio signal and video signal resulting from a failure in the transmission channel. The above-mentioned object can be achieved, in an embodiment of the present invention, by an apparatus in which the audio synchronizing block is dispersed in the video synchronizing block in the transmission. The foregoing and still other objects of the present invention, and the advantages thereof, will become fully apparent from the following description, which is to be taken in conjunction with the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic block diagram of a digital video tape recorder embodying the present invention; Figs. 2A to 2D are schematic views showing data format of video signal in the recorder shown in Fig. 1; Figs. 3A and 3B are schematic views showing data format of audio signal in the recorder shown in Fig. 1; Fig. 4 is a schematic view showing a recording format on a magnetic tape for use in the recorder shown in Fig. 1; Fig. 5 is a schematic block diagram of a digital video tape recorder constituting another embodiment of the present invention; Fig. 6 is a schematic view showing data format of video signal in the recorder shown in Fig. 5; Fig. 7 is a schematic block diagram of a digital video tape recorder constituting still another embodiment of the present invention; Fig. 8 is a schematic view showing video data to be recorded in the digital video tape recorder shown in Fig. 7; Fig. 9 is a schematic view showing audio data to be recorded in the digital video tape recorder shown in Fig. 7; Fig. 10 is a view showing the structure of a video synchronizing block in the recorder shown in Fig. 7; Fig. 11 is a view showing the structure of an audio synchronizing block in the recorder shown in Fig. 7; Figs. 12A and 12B are views showing the recording sequence of synchronizing blocks in the recorder shown in Fig. 7; Figs. 13 and 14 are views showing recording patterns on a recording medium in the recorder shown in Fig. 7; and Fig. 15 is a block diagram showing an example of the synchronizing block replacing circuit shown in Fig. 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Now the present invention will be clarified in detail by embodiments thereof shown in the attached drawings. Fig. 1 is a schematic block diagram of a digital video tape recorder (DVTR) embodying the present invention. A video input terminal 10 receives so-called component video signals. A data compression circuit 12 effects subsampling of the luminance signal Y with a rate 2f sc (f sc : subcarrier frequency) and the color signals I, Q with a rate 1/2f sc , and sends the sampled data to a video ECC encoding circuit 14 after elimination of the data of an ineffective image area, wherein the effective image ratio is taken as horizontal/vertical = 0.844/0.914. Audio signal input terminals 16, 18 receive audio signals of two channels, which are sampled at a rate of 48 KHz and digized in 16 bits respectively in A/D converters 20, 22 and are supplied to an audio interleaving circuit 24. Said circuit 24 rearranges the input data and sends said data to an audio encoding circuit 26. The encoding operation of the encoding circuits 14, 26 for video and audio signals is conducted in the following manner. The video luminance signal Y after data reduction can be considered to constitute, as shown in Fig. 2A, a two-dimensional arrangement of 240 bytes in vertical direction and 384 bytes in horizontal direction (i.e. 240 rows and 384 columns) per field, and the color signal I or Q can be considered to constitute, as shown in Fig.2B, a two-dimensional arrangement of 240 bytes in vertical direction and 128 bytes in horizontal direction (i.e. 240 rows and 128 columns) per field. Each data arrangement of said signal Y, I or Q is further divided into 12 portions as illustrated. The video encoding circuit 14 mixes a division of the signals Y, I and Q to obtain a data matrix of 60 bytes in vertical direction and 192 bytes in horizontal direction (60 rows, 192 columns), and at first effects C2 encoding in the vertical direction and adds C2 parity data of 4 bytes, whereby obtained is a two-dimensional data matrix of 64 bytes in vertical direction and 192 bytes in horizontal direction, containing C2 parity data. Then it effects C1 encoding in the horizontal direction on said data matrix and adds C1 parity data of 4 bypes, whereby obtained is a two-dimensional data matrix of 64 bytes in vertical direction and 196 bytes in horizontal direction, including C1 and C2 parity data. These data are supplied in succession, from the uppermost row, to a switch 28. For said C1 and C2 codes there may be employed already known codes such as Reed Solomon code. The audio signal, subjected to inter-leaving in the audio interleaving circuit 24, is composed of 8008 samples per 5 fields of the video signal. This is due to a fact that a field of the video signal does not exactly correspond to 1/60 seconds. However, since the processing of a leap field is not the object of the present invention, it is assumed, in the following description, that the audio signal consists of 1602 samples per field. Since the audio signal is digitized with 16 bits, 1602 samples correspond to the information of 3204 bytes. Said audio signal of 3204 bytes/field is considered to be composed, as shown in Fig. 3A, of 4 data matrixes each composed of 9 bytes in vertical direction and 94 bytes in horizontal direction. Said 4 matrixes can hold 3384 bytes (= 9 x 94 x 4), but the audio signal has only 3204 bytes per field. Thus other data of 180 bytes are inserted per field to make up data of 3384 bytes per field. The audio encoding circuit 26 effects C2 encoding operation in the vertical direction on the data matrix of 9 rows and 94 columns shown in Fig. 3A and adds C2 parity data of 3 bytes, thereby forming a data matrix of 12 rows and 94 columns including C2 parity bits. Then it effects C1 encoding on said data matrix and adds C1 parity data of 4 bytes, thereby obtaining a data matrix of 12 rows and 98 columns containing C1, C2 parity data. Said C1 and C2 encodings can be achieved with Reed Solomon codes or the like as in the video signal. Said data of 12 rows and 98 columns are released in succession, from the uppermost row, to a switch 28. The switch 28 switches the video and audio signals on time division basis. The output of the switch 28 is supplied to a synchronization adding circuit 30, where a synchronizing pattern is added. With respect to the video signal, synchronizing pattern of 1 byte is added to every two rows of the data matrix of 64 rows and 196 columns. The data of thus obtained 393 bytes will be hereinafter called synchronization block. With respect to the audio signal, a synchronizing pattern of 1 byte is added to every four rows of the data matrix of 12 rows and 98 columns, as shown in Fig. 3B. Thus a synchronization block for audio signal is also composed of 393 bytes. A modulation circuit 32 modulates the output of the synchronization adding circuit 30 to a signal form with reduced DC component, suitable for digital recording. The output of the modulation circuit 32 is amplified by a recording amplifier 34, and is magnetically recorded on a magnetic tape 38 by means of a magnetic head 36. Fig. 4 shows an example of the recording format of the magnetic tape 38, recorded by the recording apparatus shown in Fig. 1. In Fig. 4, S indicates the recording position of the synchronizing information, while A represents audio signal, and V represent video signal. Such recording format allows to significantly simplify the reproducing circuit, since separate window signals need not be formed for the video and audio signals at the detection of the synchronizing signal. The digital video tape recorder explained above allows to simplify the circuit structure, since the synchronization adding circuit 30 and ensuing circuits can be commonly used for the audio and video signals, by selecting the number of data of a synchronizing block containing audio data equal to the number of data of a synchronizing block containing video data. In the digital video tape recorder of the foregoing embodiment, data of 180 bytes are inserted to four data matrixes of the audio signal, but the insertion of meaningless data of 180 bytes is undesirable. Fig. 5 is a block diagram of a digital video tape recorder improved in this respect, and constituting another embodiment of the present invention, wherein same components as those in Fig. 1 are represented by same numbers. In Fig. 5, a sub-code generator 40 generates a cut number for video data, a signal indicating the signal form of the video and audio signals, a time code etc., which are used in the above-mentioned added codes of 180 bytes. The output of the sub-code generator 40 is supplied to the audio encoding circuit 26, and is added, as shown in Fig. 6, to 1st to 45th columns of the 1st row in the data matrix of 9 rows and 94 columns, which is generated four times in a field. Said added codes are used as control signals or editing signals in the signal reproduction. Fig. 7 is a block diagram of a digital video tape recorder constituting still another embodiment of the present invention. A terminal 101 receives luminance signal Y and color difference signals I, Q of a video signal of NTSC type in parallel manner, and said signal Y is sampled with a frequency 4f sc (f sc being color sub-carrier frequency) while the signals I, Q are sampled with a 1/4 frequency. Besides said sampling is so conducted that the sampling points are not aligned vertically in neighboring lines of interlace scanning. Thus A/D converter 102 effects so-called subsampling. The signal Y is sampled at (3.58M/15.75K) x 4/2 = 455 points per a horizontal scanning line (1H). In practice a horizontal scanning line contains 372 sampling points data are obtained only in the effective image frame. For the signal I or Q there are given 96 sampling points, which are about 1/4 of those of the signal Y. The output data of the A/D converter 102 are supplied to a memory 103, and error correcting codes (ECC) are added by an ECC addition circuit 104. An error correcting code is added to a block of video data, obtained by dividing a field into four areas in vertical direction and three areas in horizontal directions, as indicated by a hatched area in Fig. 8. If a field has 240 effective horizontal scanning lines, said block contains Y-data of the 60 (vertical) x 124 (horizontal; 372/3) sampling points, and I, Q-data of the 60 (vertical) x 32 (horizontal); (= 93/3) sampling points. These data are arranged in the memory 103 as shown in the lower half of Fig. 8, and error correcting codes C1, C2 are added as illustrated to obtain a block 192 x 64 data. The numbers in Fig. 8 indicate the number of bytes, and the data at each sampling point are composed of 8 bits (1 byte). A terminal 105 receives audio signal of 4 channels, which are sampled in an A/D converter 106 with a frequency 48 KHz and are supplied to a memory 107. There are obtained 3200 (= 48K/60 x 4) sampling points per a field of the video signal. Said 3200 samples are divided into four audio data blocks, and error correcting codes are added to each block. However, in order to form the audio data and the video data into a synchronizing data block of a same size as will be explained later, other 18 data are added, and 9 x 92 data are arranged on the memory as shown in Fig. 9. Error correction codes C1, C2 are added as illustrated, by an error correction code addition circuit 108. In the video tape recorder of the present embodiment, a field is dividedly recorded in four tracks, and each track records three video data blocks and an audio data block. These data are read from the memories 103, 107, in a unit of 384 bytes. The video signal is read by the unit of two rows from the block in Fig. 8, in a manner as shown in Fig. 10, and the audio signal is read by the unit of four rows from the block in a manner as shown in Fig. 11. A switch 109 receives a signal, of a duration required for forming a track, from a track change timing generator 110, and the data of 384 bytes are read (32 x 3) times from the memory 103 and 3 times from the memory 107 during said duration. A circuit 110 adds synchronizing data of one byte (Sync) and data (X) of 3 bytes containing a synchronizing block number and a redundancy code for said number to the above-mentioned data every 384 bytes, whereby obtained is a synchronizing block of 392 bytes. Fig. 10 shows a video synchronizing block containing video data Vd, and Fig. 11 shows an audio synchronizing block containing audio data Ad. In this manner there are obtained recording data consisting of three audio synchronizing blocks and 96 video synchronizing blocks per a track. A synchronizing block replacing circuit 111 for dispersing said audio synchronizing blocks within the above-mentioned synchronizing blocks. The three audio synchronizing blocks consecutively entered are dispersed among 96 video synchronizing blocks, as shown in Fig.12A in which shown are synchronizing blocks, A-1, A-2, A-3, V-1-1, V-1-2, ..., V-32-2 and V-32-3. The synchronizing blocks are released from said circuit 111 in an order of A-1, V-1-2, V-1-3, V-1-1, ..., V-12-1, A-2, V-13-3, V-13-1, ..., V-23-2, A-3, V-24-1, ..., V-32-2 and V-32-3. The structure of the replacement circuit 111 will be explained later. The data released from the circuit 111 are supplied, through a digital modulator 112, to a recording/reproducing unit 113 and recorded on a magnetic tape. Fig. 13 shows the positions of the audio synchronizing blocks and the video synchronizing blocks on a track of the magnetic tape. As shown in Fig. 13, the audio synchronizing blocks A-1, A-2, A-3 are in the equally divided positions in the track. Now reference is made to Figs. 12A and 12B for explaining another function of said block replacement circuit 111, wherein shown are synchronizing blocks A-1, A-2, A-3, A-1', A-2', A-3', V-1-1, V-1-2, ..., V-32-2, V-32-3. Fig. 12A shows the order of recording of synchronizing blocks on an odd track, while Fig. 12B shows that in an even track. In an odd track, the circuit 111 releases the synchronizing blocks in an order of A-1, V-1-2, V-1-3, V-1-1, ..., V-12-1, A-2, V-13-3, V-13-1, ..., V-23-2, A-3, V-24-1, ..., V-32-2, V-32-3. In an even track, the blocks are released in an order of V-1-1, V-1-2, V-1-3, .., A-1', V-6-2, V-6-3, ..., V-16-1, A-2', V-17-3, ..., V-27-1, V-27-2, A-3', ..., V-32-1, V-32-2, V-32-3. Fig. 14 shows the arrangement of the audio synchronizing blocks and the video synchronizing blocks in tracks on the magnetic tape. Thus the audio synchronizing blocks A-1, A-2, A-3 on an odd track are at positions of equally dividing the track into three. On the other hand, the audio synchronizing blocks A-1', A-2', A-3' are at positions of 1/6, 3/6 and 5/6 of an even track. Fig. 15 shows an example of the synchronizing block replacement circuit 111. A terminal 201 receives data consecutively containing audio synchronizing blocks. Said input signal is recorded, by the unit of a track, in memory 204 or 206 by means of a switch 202. The switch 202 is controlled by the timing signal shown in Fig. 7 and received through a timing signal input terminal 208, thus selecting the memory 204 or 206 at every track. The data writing into the memories 204, 206 are controlled by signals W1, W2 generated by address generators 203, 205 similarly controlled by the track timing signal, whereby the audio data are dispersed among the video data. In data reading, the address is designated by signals R1, R2 from said address generators 203, 205. The data in the memories 204, 206 are both read in the order shown in Fig. 12A in the first-mentioned example, but, in the second-mentioned example, the data of the memory 204 are read in the order shown in Fig. 12A while those of the memory 206 are read in the order shown in Fig. 12B. In the following there will be explained the reproducing function. The signal reproduced from the recording/reproducing unit is modulated in a digital demodulator 121, and is supplied to synchronization detector 122 and a data detector 124, and a block number detector 123. The synchronization detector 122 detects the synchronizing data, and clock signals generated in response to said synchronizing data are used in the data detector 124 for reproducing the data and in said block number detector 123 for detecting the block number in said data X. A synchronizing block replacement circuit 125 effects a process inverse to that conducted in the circuit 111, thus releasing 3 audio synchronizing blocks and 96 video synchronizing blocks in consecutive manner. This process utilizes the timing signal from the aforementioned circuit 110, and is confirmed by the synchronizing block numbers. A switch 126 supplies a memory 127 with the video data and a memory 128 with the audio data. These data are subjected to error correction by ECC decoding circuits 129, 130, and are converted into original analog signals by D/A converters 131, 132, and finally released from terminals 133, 134. In the video tape recorder explained above, two audio synchronizing blocks out of three can be reproduced with an extremely high probability, and, the error correction can be achieved with a considerably high probability if the audio data and the error correction data are suitably replaced in the memory 107. Also, even if the error correction is not complete; .interpolation is easy because two data blocks out of three can be securely reproduced. Thus the deterioration of the reproduced audio signal can be minimized even in case of a prolonged dropout. Besides, if the synchronizing block replacement circuit 125 performs the latter-mentioned function, the audio data will become dispersed not only along the track but also in the longitudinal direction of the tape. Consequently a scar on the tape which is frequently encountered along the track or along the longitudinal direction of the tape will not damage two consecutive audio blocks which are manually close in time, so that satisfactory reproduction is rendered possible. Besides, video blocks and also dispersed with respect to the audio blocks, so that satisfactory interpolation will become possible. In the foregoing embodiment a same recording pattern is employed in every other track, but it is also possible to repeat the same recording pattern in every n (> 2) tracks by employing n address generators in Fig. 8. Though the foregoing embodiment is limited to a digital video tape recorder, a similar effect can be obtained in a video tape recorder for recording analog video signal and time-compressed digital audio signal in time-division multiplex system, by employing different recording positions for the audio data in different tracks.

Claims: Digital signal recording apparatus comprising: means (14, 26) for forming video blocks and audio blocks having the same block length as each other from video data representative of an image, each of the video blocks containing digital video data and synchronisation data, and each of the audio blocks containing digital audio data and synchronisation data; means (28) for time division multiplexing the video blocks and the audio blocks; and means (36) for recording the video blocks and the audio blocks time division multiplexed with each other on each of a number of tracks on a recording medium (38); the apparatus being characterised in that said means for forming video blocks (14) is arranged to divide, both horizontally and vertically, a video data matrix representative of said image into a plurality of divided matrices, each corresponding to a respective divided area of said image, the digital video data included in each video block being derived from a respective one of said divided matrices. Apparatus according to claim 1 further comprising: means (14, 26, 28, 30; 101-110) operable to form a first error check code using said digital video data, and to form a second error check code using said digital audio data, each of the video blocks including the said first error check code and each of the audio blocks including the said second error check code. Apparatus according to either of the preceding claims comprising means (14) for dividing said video data matrix horizontally and vertically to form a plurality of divided matrices of luminance samples and color samples, the digital video data included in each video block corresponding to a plurality of luminance samples in a two-dimensional sample matrix and a plurality of color samples in a two-dimensional sample matrix derived from a respective one of said divided matrices. Apparatus according to any one of the preceding claims including means (111) for changing the order in which the said video blocks and the said audio blocks are recorded. Apparatus according to any one of the preceding claims when dependent on claim 2 in which the means (14, 26, 28, 30, 101-110) operable to form said first and second error check codes comprises multiplexing means (28; 109) having first input means for receiving the said digital video data and the said first error check code, second input means for receiving the said digital audio data and the said second error check code, and output means for outputting the said digital video data and the said first error check code time division multiplexed with the said digital audio data and the said second error check code. A method of recording a digital signal including the steps of: forming video blocks and audio blocks having the same block length as each other from video data representative of an image, each of the video blocks containing digital video data and synchronisation data, and each of the audio blocks containing digital audio data and synchronisation data; time division multiplexing the video blocks and the audio blocks, and recording the video blocks and the audio blocks time division multiplexed with each other on a number of tracks on a recording medium, said method being characterized by the step of: dividing, both horizontally and vertically, a video data matrix representative of said image into a plurality of divided matrices, each corresponding to a respective divided area of said image, the digital video data included in each video block being derived from a respective one of said divided matrices. A method according to claim 6 including the further steps of: forming a first error check code using said digital video data; and forming a second error check code using said digital audio data. A method according to claim 6 including the step of changing the order of the video blocks and the audio blocks. A method according to any claim dependent from claim 7 in which, following the formation of the first and second error check codes, the said digital video data and the first error check code are time division multiplexed with the said digital audio data and the second error check code. Apparatus according to claim 5 or a method according to claim 9 in which the synchronisation data is added after the digital video data and the first error check code are time division multiplexed with the digital audio data and the second error check code. Apparatus according to claim 5 or a method according to claim 9 in which the synchronisation data is added before the digital video data and the first error check code are time division multiplexed with the digital audio data and the second error check code. Apparatus according to any one of claims 1 to 5 and 11 or a method according to any one of claims 6 to 11 in which the said audio blocks also contain subcode data in addition to said digital audio data. Apparatus or a method according to claim 12 in which the subcode data comprises a time code. Apparatus according to any one of claims 1 to 5 and 11 to 13 or a method according to any one of claims 6 to 13 in which the length of digital video data contained in a said video data block is greater than the length of digital audio data in a said audio data block. Apparatus according to any one of claims 1 to 5 and 11 to 14 or a method according to any one of claims 6 to 14 in which the said time division multiplexed video blocks and audio blocks do not include consecutive audio blocks.

Inventors: KASHIDA MOTOKAZU, NAGASAWA KENICHI, SHIKAKURA AKIHIRO, YOSHIMURA KATSUJI, KASHIDA, MOTOKAZU, NAGASAWA, KENICHI, SHIKAKURA, AKIHIRO, YOSHIMURA, KATSUJI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: H04N9
IPC codes: H04N9, H04N7, G11B27