RECORDING METHOD AND APPARATUS

Abstract: Disclosed is a method and apparatus for recording an information signal, wherein when an audio signal is recorded, a start signal and an end signal indicating a unit recording duration of the audio signal are recorded together with the audio signal, and when no audio signal is present in the recording duration, the start and end signals have an inverse relationship to each other with respect to a reference level.

Description: The present invention relates to a method of recording an information signal, an apparatus which performs the method, and a medium which has been recorded with information by the method or apparatus. In particular, the invention is concerned with a method of recording an information signal, comprising the steps of: dividing the information signal into blocks; producing a start signal and an end signal for each information signal block and for at least one block which does not include part of the information signal; and recording the blocks of the information signal and the respective start and end signals. In a so-called video floppy system, for example, a method for recording an audio signal on a magnetic sheet as a recording medium in addition to a video signal has been proposed. Fig. 1 is an illustration of a magnetic sheet on which audio and video signals are recorded together. For example, under the video floppy standards, a total of 50 tracks of a field video signal (V) and audio signals (A1, A2) can be recorded on a magnetic sheet in the form of concentric tracks. The audio signal is compressed along the time base to fall in a video band, and is FM modulated to be recorded on the magnetic sheet. A recording time per track is about 10 seconds when an audio hand is at 5 kHz and a time-compression ratio is 640 times, and is about 20 seconds when the audio band is at 2.5 kHz and the time-compression ratio is 1,280 times. In this case, the audio signal can be recorded either within a single track or over two tracks or more. An audio track is divided into four sectors, as shown in Fig. 2. For example, in a 10-sec/track recording mode, 2.5 seconds of information can be recorded in a single sector. Fig. 3 shows an audio signal and an additional signal recorded within a single sector in the form of a voltage level before being FM modulated. Referring to Fig. 3, after a period t₁ has passed from time T₀, a start ID signal indicating the start timing of the audio signal continues for a period t₂, and after a blank period t₃, the audio signal starts. Note that a period t₄ is the overlap region with the previous sector, and is not present in the first sector corresponding to the starting portion of the audio signal. A remaining period t₅ corresponds to a new audio signal, and has a variable length. For example, in the 10-sec/track recording mode, the period t₅ corresponds to 2.5 seconds at maximum. After a subsequent blank period t₆, an end ID signal for indicating the end of the audio signal and obtaining a read timing of a data signal associated with the next audio signal continues during a period t₇. After a blank period t₈, the data signal associated with the audio signal continues for a period t₉, and a blank period t₁₀ having a variable length corresponding to the period t₅ of the audio signal then appears, thus completing one sector. This format is basically the same for all sectors in which audio signals are present, so that the period t₅ of the audio signal is variable, and a sum of periods t₅ and t₁₀ is constant. Therefore, positions of the end ID signal and the data signal change in accordance with the length of the audio signal. The data signal includes a track number on the magnetic sheet along which a given audio signal is recorded, a starting track number and subsequent track numbers when the audio signal is recorded over several tracks, a track number recording a video signal corresponding to the audio signal, and the compression ratio of the audio signal in the form of digital data. It has been considered by the inventors to use a combination of levels of the start and end ID signals to provide certain meanings. For example, if another audio signal is present in the next sector, the start ID signal is set at HIGH level L H and the end ID signal is set at LOW level L L with respect to a reference voltage level L₀, as shown in Fig. 4A. If the audio signal in the corresponding sector is the last one and no audio signal follows, the start and end ID signals are both set at HIGH level L H with respect to the reference voltage level L₀, as shown in Fig. 4B. If no audio signal is present in the corresponding sector, the start and end ID signals are both set at LOW level L L with respect to the reference voltage level L₀, as shown in Fig. 4C. Note that the voltage levels L₀, L H , and L L correspond to modulated frequencies f₀, f H , and f L (where f L <f₀<f H , and e.g., f₀ = 6 MHz, f H = 7 MHz, and f L = 5 MHz) after they are FM modulated. In addition, "1" level of the data signal corresponds to level L₀, and "0" level thereof corresponds to level L L . With the combination patterns of the start and end ID signals corresponding to the specific meanings, as shown in Fig. 4, when a maximum of only one sector of an audio signal is present (or a track including such a sector is present), the signal shown in Fig. 4B is recorded in the first sector, and the signal shown in Fig. 4C is recorded in the remaining second to fourth sectors. When the audio signal ends within one track, or when the audio signal continues over several tracks, the signal shown in Fig. 4A is recorded in at least the first to third sectors of the first track. As a result, average DC levels of the signals in the base band of the former and latter cases are quite different. The above-mentioned signals are FM recorded, as described above. In frequency modulation, if an input signal contains a variation in DC components, this variation appears directly as a variation in modulated frequency, thus interfering with satisfactory FM recording. For this reason, a circuit must be designed using DC coupling to reliably set an absolute DC level, thereby suppressing variation in the DC level. However, this complicates the circuit arrangement when compared with a circuit using AC coupling. STATEMENTS OF INVENTION According to the present invention, a method of recording information comprises the steps of: dividing an information signal into blocks of unit recording duration, producing a first start signal of a first polarity and a second start signal of a second polarity opposite to said first polarity with respect to a given reference level and a first end signal of said first polarity and a second end signal of said second polarity, adding said first start signal and said second end signal to each block of information preceding a last block of information signal, adding either said first start signal and said first end signal or said second start signal and said second end signal to each last block of information, adding said second start signal and said first end signal to each block following a last block of information and containing no information signal, recording each block of information signal and the respective start and end signals in sectors of a recording medium. According to the present invention, apparatus for recording an information signal comprises: means for dividing an information signal into blocks of unit recording duration, means for producing a first start signal of a first polarity and a second start signal of a second polarity opposite to said first polarity with respect to a given reference level and a first end signal of said first polarity and a second end signal of said second polarity, means for adding said first start signal and said second end signal to each block of information preceding a last block of information signal, means for adding either said first start signal and said first end signal or said second start signal and said second end signal to each last block of information, means for adding said second start signal and said first end signal to each block following a last block of information and containing no information signal, means for recording each block of information signal and the respective start and end signals in sectors of a recording medium. There follows a specific description of the invention given by way of example with reference to the drawings. Fig. 1 is an illustration showing recording tracks on a magnetic sheet; Fig. 2 is an illustration showing an audio track divided into sectors; Fig. 3 is a chart showing a format of an audio signal, ID signals, and a data signal considered by the inventors; Fig. 4 is a timing chart showing the combination patterns of start and end ID signals corresponding to specific meanings as considered by the inventors; Fig. 5 is a timing chart showing combination patterns of start and end ID signals corresponding to specific meanings when the present invention is applied to audio signal recording described with reference to Figs. 1 to 3; Fig. 6 is a format showing one track of the combination pattern of the ID signals explained with reference to Fig. 5; and Fig. 7 is a block diagram of a recording apparatus according to an embodiment of the present invention, which can form the signals in the format explained with reference to Fig. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described when the present invention is applied to audio signal recording described with reference to Figs. 1 to 3. Combinations of levels (combination patterns) of start and end ID signals corresponding to specific meanings in the present invention will first be described with reference to Fig. 5, in the same manner as for Fig. 4. Note that the same reference numerals in Fig. 5 denote the same parts as in Fig. 4. As previously described, when another audio signal is present in the next sector of a track on a magnetic recording sheet, a start ID signal is set at HIGH level L H and an end ID signal is set at LOW level L L with respect to a reference voltage level L₀, as shown in Fig. 5(A), in the same manner as in Fig. 4(A). When the audio signal in the sector of interest is the last one and no audio signal follows, the start and end ID signals are both set at HIGH level L H with respect to the reference voltage level L₀, as shown in Fig. 5(B) as in Fig. 4(B). When no audio signal is present in the sector of interest, the start ID signal is set at LOW level L L and the end ID signal is set at HIGH level L H with respect to the reference voltage level L₀, as shown in Fig. 5(C), which is the reverse of Fig. 5(A). When viewed in reference to the reference voltage level L₀, the start and end ID signals in Fig. 5(A) have an inverse relationship to each other. The ID signals in Fig. 5(B) have a non-inverse relationship, and the ID signals in Fig. 5(C) have an inverse relationship to each other, opposite to that in Fig. 5(A). The voltage levels L₀, L H and L L correspond to FM modulated frequencies f₀, f H and f L (where f L < f₀ < f H and f₀ = 6 MHz, f H = 7 MHz and f L = 5 MHz). When the combination patterns of the start and end ID signals corresponding to the specific meanings shown in Fig. 5, when a maximum of only one sector of an audio signal is present (or a track including such a sector is present), the signal shown in Fig. 5(B) is recorded in the first sector, and the signal shown in Fig. 5(C) is recorded in the following second to fourth sectors, as shown in Fig. 6(A). When the audio signal ends within one track or in the first track when the audio signal continues over several tracks, the signal shown in Fig. 5(A) is recorded in at least the first to third sectors, as shown in Fig. 6(B). As a result, a variation in average DC levels of the signals in the former and latter cases can be minimized. Therefore, when FM recording is performed, since a variation in modulated frequencies can be suppressed, recording can be successful when a simple circuit using AC coupling is adopted. Fig. 7 shows a recording apparatus which can form signals in the format of Fig. 5, and is suitable for recording. Referring to Fig. 7, an audio signal input to a terminal 1 is supplied to an A/D converter 3 through a noise-reduction circuit 2. Next, the audio signal is sampled by the A/D converter 3 based on a sampling signal of a frequency f AC , corresponding to a compression ratio of the audio signal, supplied from a controller 4 including a microcomputer or the like (to be referred to as a microcomputer hereinafter), to be converted into a digital signal. One sample of the digital audio signal is temporarily fetched by the microcomputer 4, and is then stored at a given address of a memory 6. In this case, the microcomputer 4 stores the audio signal in a given region of the memory 6, excluding a region necessary for storing the start and end ID signals and the data signal in address order, according to the format in Fig. 3. After one sector or track of audio signal is stored in the memory 6, the microcomputer 4 stores the start and end ID signal and the data signal in accordance with input data from a data input circuit 5 at remaining addresses of the memory 6. When a recording content of memory 6 is stored in the address order, it represents a signal format like that shown in Fig. 3. After the above procedure, the microcomputer 4 reads out the recording content of the memory 6 based on a PG signal from a PG detector 14 at a constant frequency (rate) f VC , and causes a D/A converter 7 to convert the readout signal into an analog signal. In this way, the D/A converter 7 outputs a compressed analog signal. In this case, if the memory 6 has a capacity corresponding to one sector, the whole content thereof can be read out in 1/240 sec, and if the capacity of the memory 6 corresponds to one track, it can be read out in 1/60 sec (assuming that a magnetic sheet 16 is rotated at 3,600 rpm). The output from the D/A converter 7 is FM modulated by an FM modulator 9 through an emphasis circuit 8, and is then supplied to a recording amplifier 10. The recording amplifier 10 is gated only during a recording period, under the control of the microcomputer 4. Thus, the FM signal is recorded on the magnetic sheet 16 through a magnetic recording head 11. The magnetic recording sheet 16 is rotated by a motor 12 at a constant speed under the control of the microcomputer 4. Assuming that one field of a video signal is recorded during a single rotation of the sheet 16, the rotating speed of the sheet 16 is 3,600 rpm on the basis of the NTSC method. A PG head 13 detects a PG mark (not shown) provided on the sheet 16. The PG detector 14 generates one pulse of PG signal per rotation of the sheet 16 based on the output from the PG head 13. The output from the PG detector 14 is supplied to the microcomputer 4, which controls a recording operation based on a recording command and the PG signal. In this case, the starting point of the first sector shown in Fig. 2 is controlled to have a given phase relationship with respect to the PG mark on the sheet 16. Positional control of the head 11 on the sheet 16 is performed by a head drive circuit 15 under the control of the microcomputer 4. Since the combination patterns of the start and end ID signals corresponding to the specific meanings are as explained in Fig. 5 and a variation in average DC levels can be suppressed, the recording apparatus of Fig. 7 can adopt a simple circuit configuration using AC coupling, and can nevertheless perform satisfactory FM recording. In the above embodiment, when no audio signal follows the sector of interest, the start and end ID signals are set at HIGH level L H with respect to the reference voltage level L₀, as shown in Fig. 5(B), but can be set at LOW level L L . In addition, the data signal can be assigned immediately after the start ID signal instead of being assigned after the end ID signal. With this format, when the recording signal is reproduced, the data signal can be quickly accessed (e.g., on a time-base expansion memory during reproduction). Therefore, audio signal reproduction can be performed without any delay. Alternatively, two memories 6 can be provided and can be assigned to odd sectors and even sectors, respectively, so that the recording signals thereof are alternately read out in units of sectors to be recorded on the sheet 16. In this case, if a memory switching timing varies slightly, the data signal can be recorded without being damaged by overwriting. A case has been exemplified wherein the present invention is applied to audio signal recording. However, the present invention is not limited to audio signal recording. According to the present invention as described above, start and end signals indicating the start and end of an information signal are added before and after the information signal, and a new combination pattern of the start and end signals having a specific meaning can reduce a variation in average DC levels of the signal. Therefore, an information recording apparatus of this type can have a simple arrangement and can prevent a variation in modulated frequencies caused by variation in average DC levels.

Claims: A method of recording information comprising the steps of: dividing an information signal into blocks of unit recording duration, producing a first start signal of a first polarity and a second start signal of a second polarity opposite to said first polarity with respect to a given reference level and a first end signal of said first polarity and a second end signal of said second polarity, adding said first start signal and said second end signal to each block of information preceding a last block of information signal, adding either said first start signal and said first end signal or said second start signal and said second end signal to each last block of information, adding said second start signal and said first end signal to each block following a last block of information and containing no information signal, recording each block of information signal and the respective start and end signals in sectors of a recording medium. A method as claimed in claim 1, further comprising the step of storing the information signal prior to the dividing step. A method as claimed in claim 1 or 2, wherein the start and end signals are of opposite polarities with respect to a reference level. A method as claimed in any preceding claim, further comprising the step of frequency modulating the blocks of the information signal and the start and end signals prior to the recording step. A method as claimed in any preceding claim, further comprising the step of time-compressing the information signal prior to the dividing step. A method as claimed in any preceding claim, wherein the information signal is an audio signal. An apparatus for recording an information signal comprising: means for dividing an information signal into blocks of unit recording duration, means for producing a first start signal of a first polarity and a second start signal of a second polarity opposite to said first polarity with respect to a given reference level and a first end signal of said first polarity and a second end signal of said second polarity, means for adding said first start signal and said second end signal to each block of information preceding a last block of information signal, means for adding either said first start signal and said first end signal or said second start signal and said second end signal to each last block of information, means for adding said second start signal and said first end signal to each block following a last block of information and containing no information signal, means for recording each block of information signal and the respective start and end signals in sectors of a recording medium. Apparatus as claimed in claim 7, further comprising means for storing the information signal prior to the dividing step. Apparatus as claimed in claim 7 or 8 in which the start and end signals are of opposite polarities with respect to a reference level. Apparatus as claimed in any one of claims 7 to 9 further comprising means to frequency modulate the blocks of the information signal and the start and end signals prior to the recording step. Apparatus as claimed in any one of claims 7 to 10 further comprising means for time-compressing the information signal prior to the dividing step. Apparatus as claimed in any one of claims 7 to 11 in which the information signal is an audio signal. Apparatus as claimed in any one of claims 7 to 12 in which the means for performing the recording step employs AC coupling. An information recording medium which has been recorded with an information signal comprising: the information signal divided into blocks, each block being recorded in a respective sector of the recording medium, either a first start signal of a first polarity or a second start signal of a second polarity opposite to said first polarity with respect to a given reference level, the start signal being recorded in each sector at the beginning of a block of information, and either a first end signal of said first polarity or a second end signal of said second polarity, said end signal being recorded in each sector at the end of a block of information, where each block of information preceding a last block of information is associated with said first start signal and said second end signal, each last block of information is associated with either said first start signal and said first end signal or said second start signal and said second end signal, each block of information following a last block of information and containing no information signal is associated with said second start signal and said first end signal. An information recording medium according to claim 14, wherein said recording medium is magnetic recording medium. An information recording medium according to claim 14, wherein said recording medium is disc shape. An information recording medium according to any one of claims 14 to 16, wherein said information signal is an audio signal. An information recording medium according to any one of claims 14 to 16, wherein said information signal is a signal which is time-compressed. An information recording medium as claimed in any one of claims 14 to 16, in which the information signal, the first start signal or the second start signal and the first end signal or the second end signal are frequency modulated and recorded on the medium respectively.

Inventors: KIMURA, NORIO, SAKATA, TGUGUHIDE, TAKEI, MASAHIRO
Applicants: CANON KABUSHIKI KAISHA
Application year: 1986
Main classification: G11B20
IPC codes: G11B20, G11B27, H04N5