1. Field of the Invention
The present invention relates to a video signal recording/reproduction apparatus (called VTR hereafter) used in recording and reproducing two kinds of video signals which carry different amounts of information, for example present video signals and HD (High Definition) video signals.
2. Description of Related Art
Conventionally, various systems of rotary head type digital signal recording and reproducing apparatus have been developed. As a typical example of such apparatuses, a digital VTR for broadcasting service known as D-2 system will be given an explanation hereinafter.
FIG. 1 is a schematic block diagram showing one example of D-2 system digital VTR. In the figure, numeral 101 is an input terminal for video signal, through which an analog video signal enters to an A/D converter 103, which converts the signal to a digital signal and outputs it to a digital recording signal processor 105. On the other hand, numeral 102 is an input terminal for an audio signal, through which an analog audio signal enters an A/D converter 104, which converts the signal to a digital signal and outputs it to the digital recording signal processor 105. The digital recording signal processor 105 carries out error-correction encoding, digital modulation, etc. and outputs the processed signal to recording AMPs 106, 107. The recording AMPs 106, 107 amplify input signals. The amplified signal is distributed to four recording and reproducing heads 112, 113, 114, and 115 via recording/reproducing selecting switches 108, 109 and via head selection switches 110, 111 and is recorded on a magnetic tape (not shown). Numerals 116-122 show components of reproducing parts. Reproducing AMPs 116 and 117 amplify signals which are reproduced on recording and reproducing heads 112, 113, 114, 115 and are transferred through switches 110, 111 and through switches 108, 109, and the amplified signal is then output to a digital reproducing signal processor 118. The digital reproducing signal processor 118 carries out digital demodulation and error-correction decoding etc., and outputs video and audio signals of normal signal strings to D/A converters 119 and 120. The D/A converter 119 converts the input signal to the original analog video signal and outputs it via an output terminal 121. The D/A converter 120 converts the input signal to the original analog signal and outputs it via an output terminal 122.
FIG. 2 shows a tape format of D-2 system digital VTR. As shown in FIG. 2, in the D-2 system, a cue, time record, and control tracks are provided in the longitudinal direction of the magnetic tape. On the track tilted in the longitudinal direction of the magnetic tape, video and audio signals are digitally recorded. The audio signal is arranged in a total of four channels; the video signals is sandwiched by four channels with two channels on either side.
Referring now to FIG. 1, operations will be described in detail hereinafter. A composite video signal supplied to the input terminal 101 is sampled at quadruple subcarrier frequency (14.318 MHz) and is converted into the digital signal of 8 quantized bits (at the A/D converter 103). The audio signal supplied to the input terminal 102 is sampled at 48 kHz and is converted into the digital signal of 20 quantized bits (at the A/D converter 104). In the figure, for simplification, the audio signal input is represented by one channel but, in practice, four channel audio signal is supplied. The digitized video and four-channel audio signals are supplied to the digital recording signal processor 105. At the digital recording signal processor 105, the video and four-channel audio signals are time-base-processed and at the same time error-correcting codes are assigned to these signals in accordance with the format. The error-correcting codes are separately assigned to the respective video and four-channel audio signals. The error-correcting codes assigned to video signals as C2 codes (also called outer codes) are (136, 128, 9) Reed-Solomon codes, and the error-correcting codes assigned to audio signals as C2 codes are (16, 8, 9) RS codes. As C1 codes (also called inner codes) (93, 85, 9) RS codes are used in common for video signals and audio signals. The digital recording signal processor 105 further performs digital modulation processing in accordance with a specified modulation system. The output signal of digital recording signal processor 105 is distributed to the recording and reproducing heads 112, 113, 114, and 115, respectively, by the head selection switches 110 and 111 via recording AMPs 106, 107 as well as recording/reproducing selecting switches 108, 109. It is then recorded on a magnetic tape in accordance with the tape format shown in FIG. 2. In this system, the data rate after the error-correcting code assigning is 127 Mbit/sec, and in terms of video signal, the data for 1 field is divided to be recorded in 6 tracks.
The recorded signal is reproduced as follows. The signal reproduced by the recording and reproducing heads 112, 113, 114, 115 enters to the digital reproducing signal processor 118 after being passed through head selection switches 110 and 111 as well as recording/reproducing selecting switches 108 and 109 and amplified by the reproducing AMPs 116, 117. The digital reproducing signal processor 118 performs digital demodulation and error-correction decoding and the signal is decoded into the normal video signal data string and the 4-channel audio signal data string to be outputted. The output signal of digital reproducing signal processor 118 is returned to the original video and 4-channel audio signals by the D/A converters 119, 120 and outputted via the output terminals 121, 122.
Video signals received in D-2 system, as described above, are video signals having 525/625 horizontal lines and field frequency of 60/50 Hz which are employed in the present television system. When such a VTR that is capable of recording high definition video signals with 1125 horizontal lines and field frequency of 60 Hz in addition to the present video signals, the amount of signals such a VTR must handle is 1.188 G bits/sec. This figure is based upon 74.25 MHz for the sampling frequency of luminance signal, 37.125 MHz for the color difference signal and 8 bits for the number of quantization bits. While recording the signals of both specifications requires the control of drum revolution speed and the number of heads, both the drum revolution speed and the number of heads can be controlled more easily when they are set in the ratio of integers. Video signal rates are not in the ratio of integers.
A technique of compressing the amount of information by applying high-efficiency encoding process to the conventional video signals is introduced in IEEE Transactions on Consumer Electronics, Vol. 34, No. 3 (AUGUST, 1988), pp 597-605, "AN EXPERIMENTAL DIGITAL VCR WITH 40 MM DRUM, SINGLE ACTUATOR AND DCT-BASED BIT-RATE REDUCTION".
FIG. 3(a) shows a block circuit diagram of the record system of the digital VTR. In FIG. 3(a), numerals 1a through 1c denote input terminals. Numerals 2a through 2c denote A/D converters to convert analog data to digital data. Numeral 3 denotes a high-efficiency encoder which applies high-efficiency encoding to input luminance signal Y and color difference signals CB and CR. Numeral 4 denotes an error correction encoder which appends error-correcting codes to 2-channel output data of the high-efficiency encoder circuit 3 for the detection or correction of errors generated during reproduction of data. Numerals 5a, 5b denote digital modulators which applies digital modulation to the output data of the error correction encoder circuit 4. Numerals 6a, 6b denote synchronization/ID appending circuits which appends synchronization signal and ID signal to the data. Numerals 7a, 7b denote recording amplifiers. Numerals 8a, 8b denote rotary heads. Numeral 9 denotes a magnetic tape.
FIG. 3(b) shows a block circuit diagram of the reproduction system of a conventional digital VTR. In FIG. 3(b), numerals 8a, 8b, 9 denote identical components as those in FIG. 3(a) and the description thereof will be omitted. Numerals 10a, 10b denote head amplifiers which amplify the signals reproduced by the rotary head amplifiers which amplify the signals reproduced by the rotary heads 8a, 8b. Numerals 11a, 11b denote data detectors which detect data from the reproduced signals and at the same time detects jitter of the reproduced signals. Numerals 12a, 12b denote digital demodulators. Numeral 13 denotes an error correction decoder which detects and corrects errors in the reproduced signals. Numeral 14 denotes a high-efficiency decoder which applies high-efficiency decoding to the output of the error correction decoder 13 and restores the video signals. Numerals 15a through 15c denote D/A converters which convert the digital signals to analog signals. Numerals 16a, through 16c denote output terminals.
Operation of the record system will now be described below with reference to FIG. 3(a). Luminance signal Y and two color difference signals CB and CR received at the input terminals 1a through 1c are A/D converted by the A/D converters 2a through 2c and are processed in the high-efficiency encoder 3 to reduce the transmission bit rate. Operation of the high-efficiency encoder is the same as that described in the literature mentioned above, and the detailed description thereof will be omitted. The data to be recorded with the transmission bit rate being reduced in the high-efficiency encoder 3 is processed in the error correction encoder 4 to be provided with error-correcting codes appended thereto for the detection and correction of errors generated during reproduction. The codes appended in this process are double RS codes of C1 (72, 56, 17) and C2 (61, 54, 8). FIG. 4 shows the data encoded with C1 and C2 (the data is called the encoded block hereafter). The data to be recorded with check signals (called check hereafter) appended thereto in the error correction encoder 4 is processed in the digital modulators 5a, 5b to suppress the low frequency components of the signal according to the specified modulation rule. Digital-modulated signals to be recorded are processed in the SYNC-ID appending circuits 6a, 6b to be provided with synchronization signal and ID signal appended thereto, then amplified by the recording amplifiers 7a, 7b and recorded onto the magnetic tape 9 via the rotary heads 8a, 8b. Eight code blocks are recorded in a single track.
Operation of the reproduction system will be described similarly with reference to FIG. 3(b). 2-channel reproduced signals which have been reproduced from the magnetic tape 9 via the rotary heads 8a, 8b are amplified by the head amplifiers 10a, 10b, then converted to digital data by the data detectors 11a, 11b while at the same time jitter (time domain error) included in the reproduced signals is absorbed. Reproduced digital data fed to the digital demodulator 12a, 12b is digital-demodulated and fed to the error correction decoder 13. The error correction decoder 13 detects and corrects errors generated in the reproduced signals based on the check which has been appended in advance during recording. Reproduced signals with errors having been detected or corrected by the error correction decoder 13 are subject to processes such as variable length decoding and inverse DCT conversion in the high-efficiency encoder 14, then with the original luminance signal Y and the two color difference signals CB and CR being restored, converted to analog data by the D/A converter circuits 15a through 15c, and provided as output through the output terminals 16a through 16c.
Conventional VTR is constituted as described above. Recording of video signals of another type by means of a digital VTR having such a recording format, for example recording of HDTV signals by applying high-efficiency encoding process to increase the amount of information twofold over that of the present TV signals with a digital VTR which compresses the information by applying high-efficiency encoding process to the present TV signals (NTSC), requires twice the number of tracks and reduces the recording time to a half, provided that recording is done with the same density. Also there has been a problem that an attempt to obtain the same recording time leads to twice the recording density which makes it difficult to make a tape and an electromagnetic conversion system which accommodates such a high recording density. Further, there has been a problem that, in order to record additional information such as the high definition TV data and the index information representing the contents of the video information in addition to the video signals, the increase in the amount of information which must be recorded results in shorter recording time if the recording density is the same.
An example of the conventional video signal recording and reproduction apparatus is the VTR of VHS system which is the most popular VTR for the use in homes and is described in "Home Video technology" published by NHK Publishing Co., Ltd. Part of the specifications of the VHS type VTR are shown in table 1.
TABLE 1 ______________________________________ Recording Video Luminance signal: FM recording, system signal Color signal: Low frequency range-converted color signal Recording SP system Audio AC current bias recording signal Drum diameter 62 mm Drum evolution 29.97 rps speed Relative speed 5.8 m/sec ______________________________________
In the VHS system, luminance signals of NTSC video signals are converted to FM signals of low-frequency carrier wave, and even white level is defined as 4.4.+-.0.1 MHz. Color signals are converted to low frequencies not higher than 1 MHz, and are superimposed with the FM waves of the luminance signals and recorded. These signals are recorded onto a magnetic tape at a rate of 1 track/field and reproduced from it by means of two heads opposing to each other separated by 180.degree. on a drum measuring 62 mm in diameter which rotates at a revolution speed of 1800 rpm.
As for the VTR system for consumer use of the high definition standard which is viewed as the next generation video system, a report is published in the Transaction of The Japan Television Engineering Association, Vol. 15, No. 50, VIR91-33, "Specifications of High Definition VTR for Consumer Use". Part of the specifications are shown in table 2.
TABLE 2 ______________________________________ Recording Video Sequential color difference lines system signal Y/C time-domain multiplexing Frequency modulation recording Audio PCM recording signal Drum diameter 62 mm Drum revolution 60 rps Relative speed 11.65 m/sec ______________________________________
Base band signals (Y, PB, PR) of the high definition television have a wide bandwidth. In order to record these signals efficiently, luminance signals and line-sequence color difference signals are time domain-multiplexed (TDM) to become TDM signals having a bandwidth of about 14 MHz: They are then D/A converted, subjected to emphasis processing and frequency modulated. These signals are recorded onto a magnetic tape in 2-channel, 2-segment format and reproduced from it by means of four (two pairs of) heads with each pair opposing to each other separated by 180.degree. on a drum measuring 62 mm in diameter which rotates at a revolution speed of 3600 rpm.
Conventional video signal recording/reproduction apparatuses are made to different specifications for the two types of video information which are incompatible to each other, such as the above NTSC and HD baseband signals. For example, the VHS system may be composed by using two heads, while HD VTR requires four heads with the drum rotating at twice higher speed. Consequently, video information of the above two types cannot be handled in a single deck. Moreover, because the bandwidths used in recording signals in the two systems greatly differ, it is difficult to commonly use key parts such as the head and the drum for the two systems. Thus manufacture of different apparatuses requires different production lines dedicated to the respective systems, resulting in high production costs.