Abstract:
Digital audio signals and a conventional audio track are recorded on a motion picture film by error correction encoding digital audio data to be recorded on the film, sequentially arranging the error encoded digital audio data in a direction perpendicular to the direction of advancement of the film by utilizing two areas or more of an area in the vicinity of one end of the film which is parallel with the other end of the film and which is laid between it and one end portion of an analog sound track or an area near the other end of the analog sound track, and recording the same.

Description:
This is a continuation of application Ser. No. 07/958,664, filed Oct. 8, 1992, now U.S. Pat. No. 5,471,263. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a digital audio signal recording method suitably applied to the case such that an audio signal is recorded on an audio track of a motion picture film in a digital fashion. 
     2. Description of the Related Art 
     In motion picture films, an analog audio signal of about two channels is recorded on a so-called sound track which is formed in the vicinity of a video recording portion. 
     According to the recent progress in digital audio technologies, it is known that an audio signal is converted into digital data and then recorded on a recording medium such as a magnetic tape or the like. Also in the motion pictures, it is requested that an audio signal can be recorded on a motion picture film in the form of a digital signal. 
     In the case of the motion picture film, however, the sound track on which the analog audio signal is recorded cannot be substantially removed from such a standpoint as to maintain a compatibility with existing film projection apparatus. Therefore, a new track on which digital audio data can be recorded must be prepared in other portion than the sound track. 
     U.S. Pat. No. 4,600,280 describes a technique in which a digital audio signal is recorded on a motion picture film together with a conventional sound track. Also, U.S. Pat. No. 5,101,397 describes a technique in which an audio signal is recorded in the form of digital audio signal. Furthermore, U.S. Pat. No. 4,461,552 describes a technique in which an audio signal is encoded according to the pulse-code-modulation (PCM) system and then optically recorded on a film. However, the above-mentioned prior arts all fail to disclose an arrangement in which words forming a digital audio signal are properly arranged on a film or addition and arrangement of an error detection and/or error correction for avoiding data error. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide a method for recording a digital audio signal on a motion picture film in which the aforesaid shortcomings and disadvantages encountered with the prior art can be eliminated. 
     More specifically, it is an object of the present invention to provide a method for recording a digital audio signal on a motion picture film in which, when a digital audio signal is optically recorded on a motion picture film or the like, digital audio data is separately recorded on a plurality of areas so that digital data of a large amount can be recorded. 
     It is another object of the present invention to provide a method for recording a digital audio signal on a motion picture film in which digital audio data is encoded so as to have error-detection and/or error-correction codes and then recorded so that data error can be avoided. 
     According to an aspect of the present invention, a digital audio signal of a plurality of channels is recorded on a motion picture film. Digital audio data is interleaved and recorded on the direction perpendicular to respective tracks formed along the travel direction of the motion picture film and parity words, used to detect and/or correct data error are generated and added to the data. 
     According to the above-mentioned arrangement, a plurality of tracks are formed by effectively utilizing portions which are not yet utilized in the motion picture film or the like. Therefore, the digital audio signal can be arranged in a block fashion and then efficiently recorded by utilizing the plurality of tracks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of other objects, features, and advantages of the present invention can be gained from a consideration of the following detailed description of illustrative embodiments thereof, in conjunction with the figures of the accompanying drawings, wherein: 
     FIG. 1 is a format of an audio data track according to an embodiment of the present invention; 
     FIG. 2 is an explanatory diagram showing a structure of a track according to the embodiment of the present invention; 
     FIG. 3 is an explanatory diagram showing a structure of one word according to the embodiment of the present invention; 
     FIG. 4 is a diagram showing a data format in a plurality of channels according to the embodiment of the present invention; 
     FIG. 5 is a diagram used to explain the location of respective words according to the embodiment of the present invention; 
     FIG. 6 is a diagram used to explain the location of CRC code according to the embodiment of the present invention; 
     FIG. 7 is a diagram used to explain how to generate P parity words according to the embodiment of the present invention; 
     FIG. 8 is a diagram used to explain how to generate Q parity words according to the embodiment of the present invention; 
     FIG. 9 is a diagram showing an arrangement of a reproducing apparatus according to the embodiment of the present invention; and 
     FIG. 10 is a diagram used to explain how to generate Q parity words according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will hereinafter be described with reference to FIGS. 1 through 10. 
     FIG. 1 of the accompanying drawings shows a track format under which digital audio data is recorded on a motion picture film. As shown in FIG. 1, a video recording portion V is formed on substantially a central portion of a motion picture film 1. An analog audio track A is formed at one end edge of the video recording portion V. An analog audio signal is optically recorded on the analog audio track A. Perforations 1a, 1b are formed on both end edge portions of the motion picture film 1 at a predetermined interval. A first digital audio data recording track D1 is formed on the motion picture film 1 between the perforations 1a and the video recording portion V. A second digital audio data recording track D2 is formed on the motion picture film 1 between the video recording portion V and the analog audio track A. A third digital audio data recording portion D3 is formed on the motion picture film 1 between the analog audio track A and the other perforations 1b. 
     In this embodiment, assuming that the width of the motion picture film 1, for example, is 35 mm, then the width of the first digital audio data recording track D1 is 425 μm, the width of the second digital audio data recording track D2 is 660 μm and the width of the third digital audio data recording track D3 is 410 μm, respectively. 
     Digital audio data of a predetermined number are separately recorded on the respective digital audio date recording tracks D1 to D3. The respective recording tracks D1 to D3 further include tracks corresponding to respective words of digital audio data. White or black patterns are exposed on the respective tracks in response to bits of respective words, thereby data being recorded. 
     FIG. 2 of the accompanying drawings shows the respective recording tracks D1 to D3 that are located close to each other in order to understand more clearly the whole arrangement of audio data separately arranged on the first to third digital audio data recording tracks D1 to D3. In FIG. 2, a square region shows one word forming digital audio data. In this embodiment, each word is composed of 16-bit data of 4 bits×4 tracks. Accordingly, there are formed tracks corresponding to respective bits. In this embodiment, there are formed 168 tracks in total in the direction perpendicular to the direction in which the motion picture film 1 is transported. 
     FIG. 3 of the accompanying drawings shows a structure of the above-mentioned one word. As shown in FIG. 3, one word comprises 4 bits in the longitudinal direction and 4 bits in the horizontal direction, i.e., 16 bits in total. In one word which constructs digital audio data, b 15  (MSB) to b 0  (LSB) of 16-bit data are arranged as shown in FIG. 3. 
     In FIG. 2, the first digital audio data recording track D1 is composed of 48 tracks (12 words). The second digital audio data recording track D2 is composed of 74 tracks (18.5 words). The third digital audio data recording track D3 is composed of 46 tracks (11.5 words). Accordingly, in the digital audio data recording tracks D1. D2 and D3, data of 48 bits, 74 bits and 46 bits are respectively arranged in the direction (horizontal direction) perpendicular to the direction in which the motion picture film 1 is advanced. According to the above track format, data of one bit occupies a square region one side of which is about 9 μm and one word occupies a square one side of which is about 36 μm. 
     As shown in FIG. 2, on 16 tracks (4 words) from the left end of the first digital audio data recording track D1, there is recorded a first parity (P parity) that is used to detect and/or correct error in digital audio data. Audio data is recorded on the following 28 tracks and synchronizing (sync.) data is recorded on the next 4 tracks (one word). 
     Sync. data is recorded on 4 tracks (one word) from the left end of the second digital audio data recording track D2. Audio data is recorded on the 70 tracks (17.5 words) which follow. 
     On 30 tracks (7.5 words) from the left end of the third digital audio data recording track D3, there is recorded audio data. A second parity (Q parity) that is used to detect and/or correct error in digital audio data is recorded on the remaining 16 tracks (4 words). 
     In this embodiment, as the sync. data recorded on the right end portion of the recording track D1 and the left end portion of the recording track D2, there is utilized sync. data of constant bit pattern which is used to detect the positions of the recording tracks D1 and D2. That is, as shown in FIG. 1, the video signal recording portion V is located between the first and second digital audio data recording tracks D1 and D2 and these recording tracks D1, D2 are thereby spaced apart. Therefore, the sync. data are respectively recorded on the first and second recording tracks D1, D2 so as to facilitate the reproduction of data. Incidentally, since a gap between the second and third digital audio data recording tracks D2 and D3 is relatively small, the data recorded on the third digital audio data recording track D3 can be reproduced with ease on the basis of the sync. data recorded on the second digital audio data recording track D2. 
     According to this embodiment, digital audio data of 8 channels can be recorded on the motion picture film 1. A data format for recording 8-channel digital audio data will be described with reference to FIGS. 4 and 5. 
     FIG. 4 of the accompanying drawings shows respective data located on respective channels at the unit of bits (sync. data is not shown). 
     FIG. 5 of the accompanying drawings shows respective data located on respective channels at the unit of words (sync. data is not shown). 
     In this embodiment, as shown in FIGS. 4 and 5, audio data of 8 channels are sequentially recorded on the tracks at every channel in the direction (horizontal direction in FIGS. 4 and 5) perpendicular to the direction in which the motion picture film 1 is advanced. A word sequence in the horizontal direction and shown on the lowermost end of FIG. 5 shows the audio data of the first channel. In this word sequence, from the left end thereof, there are recorded P parity words (P0, P1, P2, P3) of 4 words, in that order. Subsequently, data W0, W1, ..., W31) of 32 words (32 samples) which construct the first channel (CH1) are recorded which are further followed by Q parity words (Q0, Q1, Q2, Q3) of 4 words. At that time, the data (W0 to W31) of 32 words are recorded in a so-called interleave recording fashion so that data (W0, W2, W30) of even words and data (W1, W3, . . . , W31) of odd words are respectively separated. Therefore, from the left end of the audio data recording area, there are recorded data (W0, W2, . . . , W30) of even words and data (W1, W3, . . . , W31) of odd words, sequentially in that order. 
     In FIG. 5, there are provided the P parity words (P0, P1, P2, P3) which are used to error-detect and/or error-correct data sequence located in the horizontal direction. Also, in FIG. 5, there are provided the Q parity words (Q0, Q1, Q2, Q4) which are used to error-detect and error-correct data sequence located in the oblique direction of data that are arranged in a two-dimensional fashion with respect to the transport direction of the motion picture film 1 and the direction perpendicular to the direction in which the motion picture film 1 is advanced. How to generate the P and Q parity words will be described in detail later on. 
     On the second channel, there are recorded data (W0, W1, . . . W1) of 32 words, P parity words (P4 to P7) and Q parity words (Q4 to Q7) similarly to the first channel. Also in this case, the data (W0 to W31) are interleaved to data of even words and data of odd words and then recorded. In a like manner, 32-word data (W0 to W31), P parity words and Q parity words are respectively recorded up to the eighth channel. 
     In the next word sequence of the horizontal direction which follows the word sequence of the eighth channel (CH8), there are recorded data (W32, W33, . . . , W63) of 32 words, P parity words (P32 to P35) and Q parity words (Q32 to Q35) constructing the first channel (CH1) thereof. The data (W32 to W63) of 32 words are audio data which are continuous to the word sequence (W0 to W31) of the above first channel CH1. Also in this case, data (W32 to W63) are interleaved to data of even words and data of odd words and then recorded. Similarly, data (W32 to W63) are recorded in 32 words each together with P and Q parity words up to the eighth channel (CH8). 
     Error detection codes formed of CRC (cyclic redundancy check) codes are generated and recorded after two blocks of one data block from the first channel (CH1) to the eighth channel (CH8) located in the horizontal direction. In this case, the CRC codes are generated to and added to the respective tracks which are formed along the travel direction of the motion picture film 1. 
     FIG. 6 of the accompanying drawings shows the condition such that the CRC code is added to respective words located in the direction shown by an arrow a in FIG. 5. 
     As shown in FIG. 6, one word is composed of 4 tracks. The CRC code is generated to and added to 16 words which comprise words W0 of 8 channels from the first channel (CH1) to the eighth channel (CH8) constructing the first data block and words (W32) of 8 channels from the first channel (CH1) to the eighth channel (CH8) constructing the second data block. 
     The first data block, the second data block and the CRC code are repeatedly and sequentially recorded in response to the travel of the motion picture film 1. 
     How to generate and add the P parity words will be described with reference to FIG. 7, FIG. 7 of the accompanying drawings shows one word sequence in the horizontal direction shown in FIG. 5. As shown in FIG. 7, the P parity word P0 is generated from the data WO, W8, W16, W24, W1, W9, W17, W25 arranged at every four words and the Q parity word Q0. 
     Similarly, the P parity word P1 is generated on the basis of data W2, W10, W18, W26, W11, W19, W27 which are arranged at every four words and the Q parity word Q1. The P parity words P2, P3 are similarly generated on the basis of data of word sequence in which words are arranged at every four words. 
     How to generate the Q parity words (Q0, Q1, Q2, Q3) will be described with reference to FIG. 8. 
     FIG. 8 of the accompanying drawings shows only the word sequences of the horizontal direction in which data of the first channels (CH1) are recorded. As shown in FIG. 8, this word sequence comprises a word sequence in which data W0 to W31 of the first channel (CH1) are recorded, a word sequence in which data W64 to W95 of the first channel are recorded, a word sequence in which data W128 to W159 of the first channel CH1 are recorded, . . . 
     Considering a Q parity word 576 within Q parity words 576 to 579 added to the word sequence of the horizontal direction in which data W576 to W607 of the first channel CH1 are recorded, it is seen that the Q parity word 576 is generated on the basis of 9 words which are composed of the P parity word P0, data W64, data W208, . . . , data W537 as coupled by a broken line in FIG. 8. Other Q parity words are similarly generated and then interleaved. 
     Equations for generating the P parity words and the Q parity words will be described below. ##EQU1## where X in PX, QX depict each of parity word numbers, X in WX, Y depicts a channel number at which the word is located, Y depicts the word number, l depict the channel numbers 1 to 8, m depicts the integers from 0 to infinity and n depicts 0, 1, 2 and 3. 
     In this way, digital audio data of 8 channels are divided, arranged and then optically recorded on the digital audio data recording tracks D1, D2 and D3. 
     FIG. 9 of the accompanying drawings shows an arrangement of a reproducing apparatus that reproduces the digital audio data recorded on the recording tracks D1, D2 and D3 of the motion picture film 1. 
     As shown in FIG. 9, first and second CCD (charge-coupled device) line sensors 2 and 3 are disposed in the midst of the transport system of the motion picture film 1. The first CCD line sensor 2 is disposed at the position corresponding to the first digital audio data recording track D1 and the second CCD line sensor 3 is disposed at the position corresponding to the second and third digital audio data recording tracks D2 and D3. That is, since the second digital audio data recording track D2 and the third digital audio data recording track D3 are disposed close to each other, the data thereof can be detected by one CCD line sensor 3. Data of respective tracks detected by the respective CCD line sensors 2 and 3 are supplied to a digital data processor apparatus 4. In this digital data processor apparatus 4, digital audio data, recorded on the motion picture film 1, are reproduced on the basis of sync. data and digital audio data are error-detected and/or error-corrected on the basis of the P parity words, Q parity words and CRC codes, thereby reproducing the digital audio data of 8 channels. In this embodiment, the error detection is carried out mainlyby the CRC codes. 
     Since each word formed of 16 bits and relating to the error-detection and error-correction is recorded on the motion picture film 1 in a square configuration of 4 bits each in the longitudinal and horizontal directions, an error rate of erroneous data caused by a scratch in the longitudinal direction of the film is reduced to 1/4 as compared with the case such that each word formed of 16 bits is arrayed on one track in a line. Similarly, as compared with the case such that each word of 16 bits are arranged over the 16 tracks, an error rate of erroneous data caused by a scratch in the width direction of the film can be minimized. Further, since data of even words and data of odd words are interleaved, data can be interpolated with ease. 
     In addition, each track of the P parity words is generated along the horizontal direction of (i.e., width direction of the film) so that, even when an unnecessary portion of the film in the width direction is removed and the films are connected upon edition, the error correction can be carried out on the basis of at least the P parity words and the error correction becomes possible in the vicinity of edit-in. Further, since the Q parity words are interleaved during a long period Of time and then generated in the longitudinal direction of the film, a powerful error correction can be made. 
     While the positions (track) of words that are utilized to generate the Q parity words are sequentially displaced toward the right side in accordance with the word sequences of the horizontal direction according to the embodiment shown in FIG. 8, the present invention is not limited thereto and the positions (track) of words that are utilized to generate the Q parity words may be alternately displaced right and left in a zigzag fashion as shown by broken lines in FIG. 10. According to this technique, data can be interleaved in a more complex fashion, thereby making it possible to perform a more powerful error correction. 
     While data constructing each word are arranged in a two-dimensional fashion as in 4 bits×4 bits and then recorded as described above, data are not always arranged in a square fashion. However, if data are recorded in a two-dimensional fashion substantially similar to the square, then any errors caused by scratches in the longitudinal and horizontal directions can be corrected satisfactorily as described above. 
     Further, while digital audio data of 8 channels are dispersed and recorded on a number of tracks, i.e., 160 tracks (excepting the tracks for sync. data) as described above, the number of tracks and the number of channels are not limited to those in the above embodiments. As described in the above embodiments, the present invention can achieve remarkable effects when data are recorded on tracks whose number is several 10s of times the number of channels. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications could be effected therein by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims.