PCM signal recording method and apparatus

Abstract: A recording method is provided for a video tape recording apparatus having modes for recording PCM audio signals in a plurality of transmission rates. Index codes (104) for a video signal, which enable a search reproduction and so on, are recorded on a video tape in a constant transmission rate irrespective of the transmission rate of a PCM audio signal to be recorded. Further, an amble pattern (501) at the same frequency as the transmission rate of the PCM audio signal is recorded immediately behind the PCM signal recording area (102). A reproducing apparatus may be provided only with an index detecting circuit (603) corresponding to the constant transmission rate.

Description: BACKGROUND OF THE INVENTION The present invention relates to a PCM signal recording technique, and more particularly to a method and apparatus for recording PCM audio signals on a VTR recording medium such as a magnetic tape in a plurality of different transmission rates. In the 8-mm VTR, widely used is an apparatus which quantizes an audio signal in 10-bit units, compresses this 10-bit signal to an 8-bit PCM signal, and records the 8-bit PCM signal. A conventional 8-mm VTR apparatus, as a recording apparatus described in JP-A-64-86304, provides an index area between a postamble area and a video-PCM guard (V-P guard) band area, and records therein index codes called video subcodes including a search signal used for reproducing a video signal, a recording date, an absolute position, a program number and so on, so as to permit a starting position detection for a search replay. On the other hand, as a PCM audio signal, a PCM signal quantized in 16-bit units is compressed, depending on the kind of a magnetic tape, to reduce a data amount, and recorded on the magnetic tape by changing the transmission rate, as is processed by recording apparatus described in U.S. Patent 4,961,204 (DE-A-3 916 592) issued to Tanaka et al and JP-A-1-276471. The 8-mm VTR thus handles PCM signals in three different transmission rates. The above-mentioned conventional apparatus for recording a 10-bit quantized PCM signal records index codes in the same transmission rate as that of a 10-bit quantized PCM signal, and does not consider compatibility with an apparatus for recording PCM signals in a plurality of transmission rates, so that the index codes cannot be added to a 16-bit quantized PCM signal having a different transmission rate from that of the 10-bit quantized PCM signal. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for recording a signal on a video recording medium such as a magnetic tape which is capable of adding index codes for a video signal to a postamble compatibly for PCM audio signals to be recorded in a plurality of transmission rates. To achieve the above object, according to one aspect of the present invention, a method is provided as laid down in claim 1. According to another aspect of the invention, an apparatus is provided as laid down in claim 3. According to another aspect of the present invention, an area is added between the index area and the PCM signal recording area for recording an amble signal having the same transmission rate as a PCM signal. In this way, the index codes are reproduced at a constant transmission rate from any tape in the same manner irrespective of the transmission rate in which a PCM signal has been recorded thereon, whereby the index codes for video signals associated with different transmission rates can be detected by a single or common detection circuit. Also, by the postamble added immediately behind the PCM signal recording area, a reproducing clock for reproducing a PCM signal in an associated transmission rate can be derived while the postamble is being reproduced, even after PCM data has been reproduced. Since a timing margin is thus ensured upon reproducing PCM data from a tape, the PCM data can be correctly reproduced until the end thereof. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram illustrating in detail a track format according to the present invention; Fig. 2 is a diagram illustrating in detail a conventional track format; Fig. 3 is a diagram illustrating the track format in its entirety; Fig. 4 is a block diagram illustrating a PCM signal recording apparatus according to the present invention; Fig. 5 is a diagram illustrating in detail a track format according to the present invention; Fig. 6 is a block diagram illustrating an example of a reproducing circuit for reproducing a PCM audio signal and a video signal from a video tape on which signals have been recorded according to the present invention; and Fig. 7 is a diagram used for explaining the operation of the reproducing circuit shown in Fig. 6. DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will hereinbelow be described with reference to Figs. 1, 2 and 3. In the following explanation of all embodiments, it is assumed, for the purpose of illustration, that a VTR for recording a PCM audio signal and a video signal in accordance with the NTSC standard is used which is a PCM audio recording video system corresponding to three modes, i.e., an A mode for recording 16-bit quantized data, a B mode for recording 12-bit compressed data of 16-bit quantized data, and a C mode for recording 8-bit compressed data of 10-bit quantized data. The transmission rates used in the assumed system are 16.615Mbps in A mode, 13.217Mbps in B mode, and 11.580Mbps in C mode. Fig. 1 illustrates a detailed track format according to a recording method of the present invention, Fig. 3 the entire track format on a magnetic tape according to the recording method of the present invention, and Fig. 2 a detailed track format according to a recording method of the prior art. In Fig. 1, a preamble positioned at the head of an audio signal recording area is a signal of a single frequency, and PCM audio data 102 is PCM data including an audio signal error correcting code and control codes. Index codes 104 include a search signal for reproducing a video signal, a recording date, an address representing an absolute address and control codes such as a program number. An erase code 103 is a single repetitive signal for enabling overwriting of the index codes 104, and reference numeral 106 designates a video signal recording area, and 105 a V-P guard for separating a PCM signal including the index codes 104 and the video signal 106. The erase code 103 and the index codes 104 are recorded in a part of an area corresponding to a postamble 201 and a V-P guard 105 of the conventional format shown in Fig. 2. The postamble 201 is also a signal of a single frequency. Fig. 3 illustrates the whole positional relationship of the track format shown in Fig. 1 on a recording tape which is scanned by a pair of rotary heads. In Fig. 3, reference numeral 301 designates a magnetic tape, and 302, 303 margin areas in which no signals are recorded. Upon recording, the rotary heads scan and record the respective tracks shown in Fig. 3 in the direction indicated by the arrow. The recording is performed by the following processings. First, the PCM recording area signal 107 indicating an area in which the preamble 101 and PCM audio data are to be recorded, and an index recording area signal 108 indicating an area in which the index codes 104 are recorded are generated. In the PCM recording area indicated by the PCM recording area signal 107, recording is performed in accordance with a predetermined recording mode in a transmission rate selected from 16.615Mbps of A mode, 13.217Mbps of B mode, and 11.580Mbps of C mode. Next, in the index recording area indicated by the index recording area signal 108, the erase code 103 and the index code 104 are recorded in the constant transmission rate of 11.58Mbps, irrespective of a selected recording mode. Incidentally, the PCM recording area signal 107 and the index recording area signal 108 may be readily generated by a known method, i.e., by measuring a time from a reference timing which is synchronized with the rotation of a cylinder on which the recording heads are mounted. According to this embodiment, the index codes are recorded in a constant transmission rate irrespective of a transmission rate of a recorded PCM audio signal, even in a recording apparatus having modes for recording PCM audio signals in a plurality of different transmission rates. When data is reproduced from the thus recorded magnetic tape, it is not necessary to provide a plurality of index code detecting circuits corresponding to the plurality of transmission rates or recording modes. Instead, the index codes can be detected only by providing a single index code detecting circuit. Next, another embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is a block diagram illustrating an example of a recording apparatus according to the present invention. In Fig. 4, reference numeral 401 designates a system controller for controlling the whole system, 402 an index processing circuit for processing inputted index codes in accordance with a format, 404 an A and B mode PCM signal processing circuit for performing addition of an error correcting code, scramble of data and so on in the foregoing A mode or B mode, 403 a C mode PCM signal processing circuit for performing addition of an error correcting code, scramble of data and so on in the foregoing C mode, 406 an A and B mode modulation circuit for performing modulation in accordance with each of A mode and B mode, 405 a C mode modulation circuit for performing modulation in accordance with C mode, 407 a quartz oscillator for generating a clock corresponding to the transmission rate of A mode, 408 a quartz oscillator corresponding to the transmission rate of B mode, 409 a quartz oscillator corresponding to the transmission rate of C mode, 410 a clock selection and timing generation circuit for selecting a clock and generating a timing in accordance with a selected mode, 411 a video signal processing circuit for processing a video signal, 412 and 413 switch circuits respectively operated by the system controller 401 and a switch signal from the timing generation circuit 410, 414 a recording amplifier, 415 a pair of magnetic heads, 416 a rotary cylinder, 417 a magnetic tape, 418 a PCM signal input terminal, and 419 a video signal input terminal to which applied is a video signal to be recorded. Next, description will be made as to the recording operation of the above system. A PCM signal inputted from the PCM signal input terminal 418 is delivered through the switch circuit 413 to the C mode PCM signal processing circuit 403 when it is to be recorded in C mode or to the A and B mode PCM signal processing circuit 404 when it is to be recorded in A or B mode. The switch circuit 413 is controlled by the system controller 401. A control signal generated from the system controller 401, in turn, is reordered by the index processing circuit 402 in accordance with an index code format. The index processing circuit 402 also generates data for generating an erase pattern which is formed of repetition of a single frequency in proportion to the index transmission rate. The index processing circuit 402 further adds a code for detecting index errors. The PCM audio signal, after having been subjected to addition of an error correcting code, scramble of data in accordance with a recording format and so on in the PCM signal processing circuits 403 or 404, is delivered, during a period indicated in the PCM recording area shown in Fig. 1, from the C mode PCM signal processing circuit 403 to the C mode modulation circuit 405 when recorded in C mode, or from the A and B mode PCM signal processing circuit 404 to the A and B mode modulation circuit 406 when recorded in A or B mode. Data modulated by the modulation circuit 405 or 406 is inputted through the switch circuit 412 to the recording amplifier 414 and thereafter recorded on the magnetic tape 417 through the magnetic heads 415 mounted on the rotary cylinder 416. In this event, the clock selection and timing generation circuit 410 performs the following processings: 1) Generates the PCM recording area signal 107 shown in Fig. 1 based on a timing synchronized with the rotation of the rotary cylinder 416. 2) Supplies the modulation circuit 405 or 406 with a clock corresponding to the transmission rate for the PCM signal recording in each recording mode. Explaining with an example, the A and B mode modulation circuit 406 is supplied with a clock at 16.615Mbps from the quartz oscillator 407 during A mode recording, the A and B mode modulation circuit 406 is supplied with a clock at 13.217Mbps from the quartz oscillator 408 during B mode recording, and the C mode modulation circuit 405 is supplied with a clock at 11.580Mbps from the quartz oscillator 409 during C mode recording. 3) The timing generation circuit 410 controls the switch circuit 412 in the following manner. During a period indicated by the PCM recording area signal 107 of Fig. 1, the timing generation circuit 410 has the switch circuit 412 select the A and B mode modulation circuit 406 when a PCM signal is to be recorded in A mode or B mode, while the C mode modulation circuit 405 when the recording is to be performed in C mode. The index codes and the erase code processed by the index processing circuit 402 in turn are delivered to the C mode modulation circuit 405 to be modulated during a period indicated by the index recording area 108 of Fig. 1. The modulated data is inputted to the recording amplifier 414 through the switch circuit 412 during the period indicated by the index recording area 108 and thereafter recorded on the magnetic tape 417 through the magnetic heads 415 mounted on the rotary cylinder 416. Explaining the above event in greater detail, the clock selection and timing generation circuit 410 performs the following processings: 1) Generates the index recording area signal 108 shown in Fig. 1 based on the timing synchronized with the rotation of the rotary cylinder 416. 2) Supplies the C mode modulation circuit 405 with the clock at 11.580Mbps, that is, the clock corresponding to the transmission rate while a period indicated by the index recording area signal 108 lasts. 3) Simultaneously controls the switch circuit 412 so as to select the C mode modulation circuit 405 during the period indicated by the index recording area 108 shown in Fig. 1 to output the index signal to be recorded. Next, another embodiment of the present invention will be described with reference to Fig. 5. Fig. 5 illustrates a track format according to another recording method of the present invention. In Fig. 5, reference numeral 101 designates a preamble, 102 PCM audio data area (recording area), 501 a postamble having the same single frequency as the transmission rate of the PCM audio data, 104 index codes, 502 an erase code formed of a single repetitive pattern for allowing the index codes to be overwritten, 105 a V-P guard, and 106 a video signal recording area. The respective areas of the preamble 101, the PCM audio data 102, the index codes 104, the V-P guard 105, and the video signal 106 are arranged on the track in the same positional relationship as that of the track format shown in Fig. 1. Also, an area comprising the postamble 501 and the erase code 502 is equal to the erase code area 103 of Fig. 1 in view of the whole positional relationship. In the format shown in Fig. 5, recording is realized by the following processings. First, a PCM recording area signal 107 indicating an area in which the preamble 101, the PCM audio data 102 and the postamble 501 are recorded and an index area signal 108 indicating an area in which the erase code 502 and the index codes 104 are recorded are generated. In a PCM recording period indicated by the PCM recording area signal 107, the preamble 502, the PCM audio data 102 and the postamble 501 are recorded in a transmission rate selected from 16.615Mbps, 13.217Mbps and 11.580Mbps in accordance with a required recording mode. Next, in an index recording period indicated by the index recording area signal 108, the erase code 502 and the index codes 104 are recorded at a constant transmission rate, for example, 11.580Mbps, irrespective of the required recording mode. In a manner similar to the embodiment explained in connection with Fig. 1, the PCM recording area signal 107 and the index recording area signal 108 may be readily generated by measuring a time from a reference timing synchronized with the rotation of a cylinder on which a pair of recording heads are mounted. Next, explanation will be given of numerical examples of the postamble 501, the erase code 502, the index codes 104 and the V-P guard 105 of the embodiment shown in Fig. 5. Assume in the following explanation that reference letter H designates the length of an area corresponding to one horizontal synchronization period of a video signal, and the lengths of the respective areas are expressed with "H" as the unit. First, as standard values, the postamble is determined to be 0.1H long, the erase code 2.6H, the index code 1.8H, and the V-P guard 2.3H. The total length of the five areas, that is, the area between the PCM audio data 102 and the video signal 106 is 6.8H. By determining in the above manner, no inconvenience will occur even if the following variations of apparatus are taken into consideration. The variations to be considered to be tolerable are the recording position accuracy of the PCM audio data 102 lying within ± 0.8H, and the recording position accuracy of the video signal 106 within ± 1.5H. In this case, the length of the area between the PCM audio data 102 and the video signal 106 is 6.8H ± 2.3H. The recording area for the erase code 502 is assumed to be a variable area extending from the end of the postamble 501 to a position 4.1H before a head switching point. (The head switching point refers to a timing at which signals reproduced from the two opposed magnetic heads 415 spaced by 180° are switched in order to produce a single sequential signal from these signals.) This assumption ensures the respective areas included between the PCM audio data 102 and the video signal 106 as follows even in the following worst cases: (a) The region between the PCM audio data 102 and the video signal 106 extends over 6.8H-2.3H: 1) Preamble 0.1H 2) Erase code 2.6H-0.8H 3) Index code 1.8H 4) V-P guard 2.3H-1.5H (b) The region between the PCM audio data 102 and the video signal 106 extends over 6.8H + 2.3H: 1) Preamble 0.1H 2) Erase code 2.6H + 0.8H 3) Index code 1.8H 4) V-P guard 2.3H + 1.5H According to the embodiment shown in Fig. 5, since the postamble is recorded immediately behind the PCM audio signal in the same transmission rate as that of the PCM audio signal, a clock at a frequency equal to the transmission rate of the PCM audio signal can be reproduced while the postamble is reproduced from the magnetic tape 417 during reproducing the PCM audio signal. A PCM audio signal processing circuit therefore can continuously supply the clock at the transmission rate of the PCM audio signal reproduced from the postamble until the last data of the PCM audio signal has been processed, thereby making it possible to correctly reproduce until the last data of the PCM audio signal. Next, an example of a circuit for reproducing a PCM audio signal and a video signal recorded on a magnetic tape in accordance with the above described embodiment will be described with reference to Figs. 6 and 7A-7D. Fig. 6 is a block diagram of a reproducing circuit for reproducing a PCM audio signal and index codes for a video signal, and Figs. 7A-7B are timing charts showing operation timings of the reproducing circuit shown in Fig. 6 when a PCM audio signal is recorded in A mode. The transmission rate of the preamble and A mode PCM audio data is determined to be 16.615Mbps and that of the erase code 103 and the index codes 104 11.580Mbps. In Fig. 6, reference numeral 415 designates a pair of magnetic heads, 416 a rotary cylinder, 417 a magnetic tape, 601 a reproducing amplifier, 602 a clock reproducing circuit for reproducing from a reproduced signal a clock synchronized with the reproduced signal, 603 a demodulation circuit for demodulating a PCM audio signal and the index codes 104 recorded in the transmission rate of C mode, 604 a demodulation circuit for demodulating a PCM audio signal recorded in A mode or B mode, and 605 a timing circuit for generating, based on a head switching timing, a switch control signal to the clock reproducing circuit as well as an operation enable timing signal to the demodulation circuits 603, 604. The head switching timing (Fig. 7D) is a switching signal for switching the two opposed magnetic heads 415 spaced by 180° so as to produce a single sequential signal from signals reproduced from these magnetic heads, and generated by a servo circuit of the rotary heads, not shown in Fig. 6. Next, description will hereinbelow be made as to the operation, in order, of reproducing a PCM audio signal which has been recorded in A mode. Signals detected by the magnetic heads 415 are delivered through the reproducing amplifier 601 to the clock reproducing circuit 602. The clock reproducing circuit 602 detects "1" and "0" states of the reproduced data using a reproduced clock, and outputs the detected data together with the reproduced clock. The clock reproducing circuit 602 may be constituted of an ordinary phase locked loop (PLL). In the present embodiment, since signals in different transmission rates are processed, the central frequency of the PLL is switched for each transmission rate. The clock reproducing circuit 602 therefore switches the central frequency of the PLL in accordance with a switching timing shown in Fig. 7B to handle and supply the detected data and transmission clock synchronized with the data to the C mode demodulation circuit 603 and the A and B mode demodulation circuit 604. The A and B mode demodulation circuit 604 demodulates an A mode PCM audio signal during an A mode period in Fig. 7C in accordance with an operation enable timing from the timing circuit 605, while the C mode demodulation circuit 603 demodulates the index codes 104 during a C mode period in Fig. 7C in accordance with the operation enable timing from the timing circuit 605. When a recorded PCM audio signal is in B mode, the only difference appears in that the A and B mode demodulation circuit 604 demodulates the PCM audio signal in B mode. It will be thus appreciated that the index codes for a video signal recorded in accordance with the present invention can be detected by a single detecting circuit, i.e., the C mode demodulation circuit 603.

Claims: A method of recording a PCM audio signal at a plurality of different transmission rates and a video signal on a recording medium comprising the steps of: recording said PCM audio signal in a predetermined first region (102) on the recording medium at a first transmission rate selected from said plurality of transmission rates; and recording index codes representing video subcodes in a second region (104) of the recording medium different from said first region characterised in that said index codes are recorded at a constant second transmission rate independent of said first transmission rate. The recording method according to claim 1 further including the step of recording an amble signal comprised of a single repetitive signal at the same rate as said first transmission rate in a portion (501) of said second region provided between said first region and said index codes. An apparatus for recording a PCM audio signal at a plurality of different transmission rates and a video signal on a recording medium comprising: means (403 ~ 411, 414, 415) for recording said PCM audio signal in a predetermined first region (102) and said video signal in a third region (104) behind said first region on the recording medium (417) in a first transmission rate selected from said plurality of transmission rates; and means (402, 405, 409 ~ 410, 414 ~ 415) for recording index codes representing video subcodes in a second region (104) between said first and third regions at a constant second rate irrespective of said first transmission rate. A recording apparatus according to claim 3 further including means (403 ~ 410, 414 ~ 415) for recording an amble signal comprised of a single repetitive signal at the same rate as said first transmission rate in a fourth region (501) immediately behind said first region. A method according to claim 1, wherein said index codes include a program starting position, a recorded date, an absolute position and a program number. A method according to claim 1, wherein said constant second transmission rate comprises one of said plurality of different transmission rates. A method according to claim 1, wherein the recording medium is a magnetic tape, recording is performed using rotary heads, said video signal is recorded in a third region (106) succeeding said second region, wherein the transmission rate of the PCM audio signal depends on a recording mode. A method according to claim 7 further including the step of dividing said second region into a region for recording an amble signal (501) comprised of a single repetitive signal at the same rate as said first transmission rate, a region (502) for recording an erase code and a region (104) for recording the index codes for a video signal.

Inventors: ARAI TAKAO, ITOH SHIGEYUKI, NAGAI YUTAKA, NOGUCHI TAKAHARU, OKAMOTO HIROO, TAKEUCHI TOSHIFUMI, ARAI, TAKAO, ITOH, SHIGEYUKI, NAGAI, YUTAKA, NOGUCHI, TAKAHARU, OKAMOTO, HIROO, TAKEUCHI, TOSHIFUMI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1992
Main classification: G11B27
IPC codes: G11B27, G11B20