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:
BACKGROUND OF THE INVENTION 
     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. 
     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 the picture area. 
     According to the recent progress in digital audio technologies, it can be 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 picture films it has been requested that the audio signal be recorded on the motion picture film in the form of a digital signal. 
     In the case of motion picture film, however, the conventional sound track on which the analog audio signal is recorded cannot be removed to maintain 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 art fail to disclose an arrangement in which the words forming a digital audio signal are properly arranged on the film or the addition and arrangement of 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 above-stated shortcomings and disadvantages of 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, the digital audio signal is separately recorded in plural digital soundtracks so that a large amount of digital data 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 signal is encoded to include error-detection and/or error-correction codes and then recorded so that signal errors can be avoided. 
     Accordingly, the present invention provides a method for recording a digital audio signal on a motion picture film. The digital audio signal is recorded in addition to a conventional analog soundtrack. According to the method, error correction code is added to the digital audio signal to provide a coded digital audio signal. The coded digital audio signal is sequentially arranged into rows. The coded digital audio signal arranged into rows is recorded on the motion picture film in two digital soundtracks. Each row is recorded in each digital soundtrack in a direction perpendicular to the direction of travel. Successive rows are recorded in the direction of travel of travel of the film. One of the digital soundtracks is located near one edge of the motion picture film. The other digital soundtrack is located near the other edge of the motion picture film in one of two positions. The first position is between the other edge of the film and one edge of the analog sound track; the second position is near the other edge of the analog sound track. 
     The invention also provides a motion picture film with digital and analog sound tracks. The motion picture film comprises a picture area, an analog sound track, and first and second digital soundtracks. The first and second digital soundtracks are located on the motion picture film and run in the direction of travel of the motion picture film. The second digital soundtrack is located on the motion picture film in one of two positions. The first position is between one edge of the picture area and one edge of the analog soundtrack. The second position is near the other edge of the analog sound track. The first digital soundtrack is located near the other edge of the picture area. Recorded in the digital soundtracks is a coded digital audio signal comprising a digital audio signal to which error correction code has been added. The coded digital audio signal is sequentially arranged into rows, and successive rows are recorded in the digital soundtracks in the direction of travel. 
    
    
     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 illustrates the format of the digital soundtrack according to the present invention; 
     FIG. 2 is an explanatory diagram showing a structure of the digital audio soundtrack according to the present invention; 
     FIG. 3 is an explanatory diagram showing a structure of one word of the digital soundtrack according to the present invention; 
     FIG. 4 is a diagram showing the data format in plural channels according to the present invention; 
     FIG. 5 is a diagram used to explain the location of respective words according to the present invention; 
     FIG. 6 is a diagram used to explain the location of CRC code in the digital soundtrack according to the present invention; 
     FIG. 7 is a diagram used to explain how to generate P parity words in the digital soundtrack according to the present invention; 
     FIG. 8 is a diagram used to explain how to generate Q parity words in the digital soundtrack according to the present invention; 
     FIG. 9 is a diagram showing an arrangement of a reproducing apparatus for reproducing the digital soundtrack according to the present invention; and 
     FIG. 10 is a diagram used to explain how to generate Q parity words in a different embodiment of the digital soundtrack according to 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 in which a digital audio signal is recorded on a motion picture film. As shown in FIG. 1, the picture area V is formed on substantially a central portion of a motion picture film 1. An analog soundtrack A is formed at one end edge of the picture area V. An analog audio signal is optically recorded on the analog soundtrack A. Perforations 1a, 1b are formed on both end edge portions of the motion picture film 1 at a predetermined interval. A first digital soundtrack D1 is formed on the motion picture film 1 between the perforations 1a and the picture area V. A second digital soundtrack D2 is formed on the motion picture film 1 between the picture area V and the analog soundtrack A. A third digital soundtrack 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 soundtrack D1 is 425 μm, the width of the second digital soundtrack D2 is 660 μm and the width of the third digital soundtrack D3 is 410 μm. 
     A predetermined number of words of a digital audio signal is separately recorded on the respective digital soundtracks D1 to D3. The respective soundtracks D1 to D3 include tracks corresponding to the respective words of the digital audio signal. White or black patterns are exposed on the respective digital soundtracks in response to bits of the respective words to record the digital audio signal. 
     FIG. 2 of the accompanying drawings shows the respective soundtracks D1 to D3 that are located close to each other in order to understand more clearly the whole arrangement of the digital audio signal separately arranged on the first to third digital soundtrack D1 to D3. In FIG. 2, a square represents one word of the digital audio signal. In this embodiment, each word is composed of 16 bits arranged into 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 of travel of the motion picture film, i.e., 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 lateral direction, i.e., 16 bits in total. In one word of the digital audio signal bits, b 15  (MSB) to b 0  (LSB) of the 16-bit word are arranged as shown in FIG. 3. 
     In FIG. 2, the first digital soundtrack D1 is composed of 48 tracks (12 words). The second digital soundtrack D2 is composed of 74 tracks (18.5 words). The third digital soundtrack D3 is composed of 46 tracks (11.5 words). Accordingly, in the digital soundtracks D1, D2 and D3, 48 bits, 74 bits and 46 bits are respectively arranged in the lateral direction perpendicular to the direction of travel of the motion picture film 1. According to the above track format, 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 the 16 tracks (4 words) closest the left edge of the first digital soundtrack D1, there is recorded a first parity (P parity) word that is used to detect and/or correct error in the digital audio data. Audio data is recorded on the next 28 tracks and synchronizing (sync.) data is recorded on the next 4 tracks (one word). 
     Sync. data is also recorded on the 4 tracks (one word) closest to the left edge of the second digital soundtrack D2. The audio signal is recorded on the next 70 tracks (17.5 words). 
     On the 30 tracks (7.5 words) closest to the left edge of the third digital soundtrack D3, there is recorded the audio signal. A second parity (Q parity) word that is used to detect and/or correct error in digital audio signal is recorded on the remaining 16 tracks (4 words). 
     In this embodiment, the sync. data recorded at the right edge portion of the recording track D1 and the left edge portion of the soundtrack D2, has a constant bit pattern which is used to detect the positions of the soundtracks D1 and D2. That is, as shown in FIG. 1, the picture area V is located between the first and second digital soundtracks 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 soundtracks D1, D2 so as to facilitate the reproduction of the digital audio signal. Incidentally, since the gap between the second and third digital soundtrack D2 and D3 is relatively small, the signal recorded on the third digital soundtrack D3 can easily be reproduced using the sync. data recorded on the second digital soundtrack D2. 
     With this arrangement a digital audio signal representing 8  channels can be recorded on the motion picture film 1. The format for recording an 8-channel digital audio signal will be described with reference to FIGS. 4 and 5. 
     FIG. 4 of the accompanying drawings shows the channel signals of the respective channels at the unit of bits (sync. data is not shown). 
     FIG. 5 of the accompanying drawings shows the channel signals of the on respective channels at the unit of words (sync. data is not shown). 
     In this embodiment, as shown in FIGS. 4 and 5, the channel signal of 8 channels are sequentially recorded on the digital soundtracks, with the channel signal of each channel successively arranged in the lateral direction (shown horizontally in FIGS. 4 and 5), perpendicular to the direction of travel of the motion picture film 1. The word sequence in the lateral direction and shown on the lowermost end of FIG. 5 shows the digital audio signal of the first channel. In this word sequence, from the left end thereof, there are recorded 4P 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 and are further followed by 4Q parity words (Q0, Q1, Q2, Q3). The 32 words (W0 to W31) are recorded in a so-called interleave recording fashion so that the even words (W0, W2, . . . , W30) and the odd words (W1, W3, . . . , W31) are separated. Therefore, from the left edge of the soundtrack, there are recorded the even words (W0, W2, . . . , W30) and odd words (W1, W3, . . . , W31) 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 lateral 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 array with respect to the direction of travel the motion picture film 1 and the direction perpendicular to the direction of travel of the motion picture film 1. How to generate the P and Q parity words will be described in detail later on. 
     On the second channel, there are recorded 32 words of the first channel signal (W0, W1, W1), 4P parity words (P4 to P7) and 4Q parity words (Q4 to Q7) similarly to the first channel. Also in this case, the data (W0 to W31) are interleaved to words of even words and odd words and then recorded. In a like manner, 32 words of channel signal (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 lateral direction which follows the word sequence of the eighth channel (CH8), there are recorded 32 words of the channel signal (W32, W33, . . . , W63), 4P parity words (P32 to P35) and 4Q parity words (Q32 to Q35) constructing the first channel (CH1) thereof. The 32 words of the first channel signal (W32 to W63) continue to the word sequence (W0 to W31) of the above first channel CH1. Also in this case, words (W32 to W63) are interleaved into even words and data of odd words and then recorded. Similarly, 32 words of the channel signal (W32 to W63) are recorded 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 signal block from the first channel (CH1) to the eighth channel (CH8) located in the lateral 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 signal block and words (W32) of 8 channels from the first channel (CH1) to the eighth channel (CH8) constructing the second signal block. 
     The first signal block, the second signal 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 lateral direction shown in FIG. 5. As shown in FIG. 7, the P parity word P0 is generated from the words W0, W8, W16, W24, W1, W9, W17, W25, which are 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 the 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 lateral direction in which channel signals of the first channels (CH1) is recorded. As shown in FIG. 8, this word sequence comprises a word sequence in which words W0 to W31 of the first channel (CH1) are recorded, a word sequence in which words W64 to W95 of the first channel are recorded, a word sequence in which words W128 to W159 of the first channel CH1 are recorded, . . . 
     Considering the Q parity word 576 within Q parity words 576 to 579 added to the word sequence of the lateral direction in which words 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, words W64, words W208, . . . , words W537 indicated by the 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 P x , Q x  indicates the word number, X in W x  indicates the channel number at which the word is located, Y depicts the word number, l depict the channel numbers 1 to 8, m indicates the integers from 0 to infinity and n indicates 0, 1, 2 and 3. 
     In this way, a digital audio signal of 8 channels is divided, arranged and then optically recorded on the digital soundtracks D1, D2 and D3. 
     FIG. 9 of the accompanying drawings shows an arrangement of a reproducing apparatus that reproduces the digital audio signal 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 within 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 soundtrack D1 and the second CCD line sensor 3 is disposed at the position corresponding to the second and third digital soundtrack D2 and D3. That is, since the second digital soundtrack D2 and the third digital soundtrack D3 are disposed close to each other, the digital audio signal recorded thereon can be detected by one CCD line sensor 3. The digital audio signals recorded in the respective tracks detected by the respective CCD line sensors 2 and 3 are supplied to the digital signal processor apparatus 4. In this digital data processor apparatus 4, the digital audio signal, recorded on the motion picture film 1, is reproduced on the basis of sync. data and the digital audio signal is 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 signals of 8 channels. In this embodiment, the error detection is carried out mainly by 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 lateral directions, the 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 in which each word formed of 16 bits is linearly arrayed on one track. Similarly, compared with the case in which each word of 16 bits in linearly arranged over the 16 tracks, the error rate of erroneous data caused by a scratch in the width direction of the film is minimized. Further, since even words and odd words are interleaved, data can be interpolated with ease. 
     In addition, each track of the P parity words is generated along the lateral direction of the film so that, even when a portion of the film is removed and the film is spliced during editing the error correction can be carried out on the basis of at least the P parity words. Thus, error correction can still be carried out in the vicinity of a splice in the film. Further, since the Q parity words are interleaved over a long period of time and are then generated in the longitudinal direction of the film, powerful error correction can be made. 
     While the tracks in which are of words used to generate the Q parity words are sequentially displaced to the right in accordance with the word sequences of the lateral direction according to the embodiment shown in FIG. 8, the present invention is not limited thereto and tracks in which the words used 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 more powerful error correction. 
     While each word is arranged in a two-dimensional array as in 4 bits×4 bits and then recorded as described above, words need not be arranged in a square fashion. However, if words are recorded in a two-dimensional array 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 the digital audio signals 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 the digital audio signal is 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.