Magnetic recording and reproducing apparatus

Abstract: A magnetic recording and reproducing apparatus capable of recording video, audio and other information on a magnetic tape by, for example, the helical scanning method. A rotary head is rotated at an m-fold speed to record intermittent tracks on the magnetic tape so that real-time simultaneous monitoring is performed. By high-speed dubbing due to high-density intermittent recording and by increasing the number of repetition of track scanning, the information is recorded and reproduced simultaneously with a plurality of channels. Any tracking error is detected to form a continuous and uniform track pattern. With this intermittent comb-shaped recording, reciprocating recording and reproducing can be realized.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: This invention relates to a magnetic recording and reproducing apparatus for recording video and audio information on a magnetic tape in a helically scanning system. 2. Description of the Related Art: For accurately recording a digital video signal and a digital audio signal by a digital video tape recorder, it has hitherto necessary to confirm the state of recording by reproducing the recorded data soon after recording, namely, to perform simultaneous monitoring. FIG. 16 shows the location of magnetic heads in a prior art magnetic recording and reproducing apparatus exemplified by Japanese Patent Laid-Open Publication No.61165801/1986. FIG. 17 shows a track pattern of recording onto a magnetic tape by the magnetic heads. In FIG. 16, a pair of first magnetic heads 301-1, 301-2 are arranged on the peripheral edge of a rotary drum 302 and are angularly spaced from each other by 180°, and likewise, a pair of second magnetic heads 301-3, 301-4 are arranged on the peripheral edge of the rotary drum 302 and are angularly spaced from each other by 180°. The second magnetic heads 301-3, 301-4 are angularly spaced from the first magnetic heads 301-1, 301-2, respectively, by 90°. In FIG. 17, the magnetic tape 310 is fed in the direction of an arrow R. 311-1 designates a track recorded by the first magnetic head 301-1; 311-2, a track recorded by the second magnetic head 301-3; 311-3, a track recorded by the first magnetic head 301-2; and 311-4, a track recorded by the second magnetic head 301-4. These four recording tracks 311-1 through 311-4 constitute one frame of recording data. FIG. 18 is a block diagram showing recording signal processing system when digitally recording 2-channel video signals simultaneously in the arrangement and track pattern of the magnetic heads of FIGS. 16 and 17. A first low-pass filter (hereinafter called "first LPF") 350 performs a band restriction to sample a first video signal. A second LPF 350-2 performs a band restriction of a second video signal. A first A/D converter 351-1 samples the first video signal, and a second A/D converter 351-2 samples the second video signal. A first encoder 352-1 encodes digital data from the first A/D converter 351-1 by adding an error correcting code thereto. A second encoder 352-2 encodes digital data from the second A/D converter 351-2 in the same manner. A first memory 338-1 is used in encoding by the first encoder 352-1, and a second memory 338-2 is used in encoding by the second encoder 352-2. A first modulator 353-1 encodes the digital data, which were encoded by the first encoder 352-1, into optimum recording codes suitable for magnetic recording and reproducing. A second modulator 353-2 encodes the digital data, which were encoded by the second encoder 352-2, into optimum recording codes suitable for magnetic recording and reproducing. A first recording head amplifier 342-1 drives the first magnetic heads 301-1, 301-2 based on the output of the first modulator 353-1. A second recording head amplifier 342-2 drives the second magnetic heads 301-3, 301-4 based on the output of the second modulator 353-2. FIG. 19 is a diagram showing the arrangement of magnetic heads and the operating period of each magnetic head for recording, with respect to the first and second channel recording data. The first and second channels correspond to the respective outputs of the first and second modulators 353-1, 353-2. In operation, in two-channel recording and reproducing, the magnetic tape 310 is fed at a speed two times higher than ordinary. At that time, the first magnetic heads 301-1, 301-2, which are arranged on the rotary drum 302 and are angularly spaced from each other by 180°, record and reproduce a video signal. Meanwhile, the second magnetic heads 301-3, 301-4 record and reproduce an audio signal, a different video signal or the like. In this case, the recording track pattern on the magnetic tape 310 by the first and second magnetic heads 301-1, 301-2, 301-3, 301-4 is shown in FIG. 17. Specifically, the track 311-1 is recorded by one (301-1) of the first magnetic heads 301-1, 301-2, and the track 311-2 is recorded by one (3-1-3) of the second magnetic heads 301-3, 301-4. Likewise, the track 311-3 is recorded by the other (301-2) of the first magnetic heads 301-1, 301-2, and the track 311-4 is recorded by the other 301-4 of the second magnetic heads 301-3, 301-4. Accordingly, two pieces of information are recorded at every rotation of the rotary drum 302. The mode of operation of the recording signal processing system in, for example, digitally recording two-channel video signals will now be described. Although there is no illustration of the audio signal processing system, audio signals like the video signals are digitally recorded. In FIG. 18, the first and second channel video signals are restricted in band so that the first and second LPFs 350-1, 350-2 allows the video signal band to pass. Then, the video signals are sampled at a frequency more than two times higher than the video signal band by the first and second A/D converters 351-1, 351-2. Generally, in NTSC system, the video signal band is about 4.5 MHz, and it is necessary to sample the video signal by a frequency higher than 9 MHz according to Nyquist's theorem. Since a color signal is transmitted as a carrier of 3.58 MHz is perpendicular-two-phase modulated, it is customary to set the sampled frequency multiple by an integer over 3.58 MHz in view of beat interference with the sampled frequency. From these relations, very occasionally the sampled frequency is set to 3·f sc (f sc stands for a carrier frequency of 3.58 MHz, and 3·f sc stands for about 10.7 MHz) and 4·f sc (about 14.3 MHz). The thus digitized recording video data are encoded by the first and second encoders 352-1, 352-2 in such a manner that the errors occurred during magnetic recording and reproducing can be corrected. Here the first and second memories 338-1, 338-2 are used in encoding. Then the encoded data are encoded by the first and second modulators 353-1, 353-2 so as to be the optimum data suitable for magnetic recording and reproducing. This encoding system is exemplified by NRZ and NRZI systems. Subsequently, the modulated recording video data are recorded on the magnetic tape 310. Specifically, the first and,second channel digital data are recorded by the first magnetic heads 301-1, 301-2 and the second magnetic heads 301-3, 301-4 via the first and second recording head amplifiers 342-1, 342-2, respectively. Here the arrangement of the magnetic heads of the two-channel recording data are shown in FIG. 19. Specifically, DATA1-1 of the first channel is recorded on the track 311-1 by the first magnetic head 301-1, while DATA1-2 of the first channel is recorded on the track 311-3 by the first magnetic ahead 301-2. Likewise, DATA2-1 of the second channel is recorded on the track 311-2 by the second magnetic head 301-3, while DATA2-2 of the second channel is recorded on the track 311-4 by the second magnetic head 301-4. By the foregoing operation, two-channel video signals can be recorded simultaneously. Also in reproducing, two-channel video signals can be reproduced simultaneously by tracing the track. With this prior art magnetic recording and reproducing apparatus, in order to record two-channel video signals, it is necessary to add two magnetic heads. Also, two signal processing circuits are necessary. Further, it is impossible to do recording at one channel, while reproducing at the other channel. SUMMARY OF THE INVENTION With the foregoing prior art problems in view, the object of this invention is to enable recording through one channel and, at the same time, reproducing through the other channel, without adding any magnetic head, increasing any circuit components and hence increasing the cost of production. This object is achieved by a magnetic recording and reproducing apparatus having the features indicated in claim 1. The invention is further developed by the features mentioned in the subclaims. With this arrangement, a plurality of channels can be dealt with simultaneously; this is, n-channel recording and reproducing is possible. During n-channel recording and reproducing, the magnetic head scans n tracks during one-channel recording and reproducing under the control by the scanning control means. As a result, n-channel recording signals can be recorded on n tracks, or n-channel reproducing signals can be reproduced from n tracks. With the arrangement, it is unnecessary to provide an additional magnetic head and signal processing circuit for each channel. Accordingly, multichannel signal can be dealt with with simple construction. The apparatus includes a channel composing and separating means. This channel composing and separating means composes recording signals of the individual channels during recording, and separates reproducing signals of the individual channels during reproducing. Therefore, for example, n-channel recording signals can be distributed and recorded on n tracks during recording, and reproducing signals to be reproduced from n tracks can be outputted as distributed to channels. Since the recording and reproducing by the magnetic head is conducted in units of tracks, recording and reproducing through a plurality of channels to be dealt with simultaneously, e.g., one channel for recording and another for reproducing, can coexist. The channel composing and separating means include a tape speed control means and may include an identification code adding means and an identification code separating means. The tape speed control means controls the speed of feed of the magnetic tape. The identification code adding means adds to a recording signal an identification code indicating the speed of feed of the magnetic tape and causes the magnetic head to record the identification code in a predetermined portion of the track on the magnetic tape during recording. The identification code separating means separates and detects an identification code from a reproducing signal and instructs the tape speed control means to control the feed speed of the magnetic tape to a target feed speed during reproducing. As a result, it is possible to use the space of the magnetic tape effectively, irrespective of the speed of feed of the tape. preferably, the identification codes should include those indicating the feed speeds of the individual tapes, and those indicating that the magnetic tape is in a transitional position where the feed speed of the tape is being switched. Specifically, during the transitional period in which the feed speed of the magnetic tape is being switched by the tape speed control means, the identification code adding means adds to the recording signal the identification code of this content (i.e., the content different from that when the tape is being fed at a constant speed), and the resulting signal is recorded on the magnetic tape. The identification code separating means detects the identification codes during reproducing and instructs to change the feed speed of the tape. As a result, it is possible to make shift between n-channel recoding and reproducing and one-channel recording and reproducing smoothly and reliably. n-Channel recording and reproducing may be such that the timing of supplying and taking out the signals to and from the magnetic ahead depends on the channel. By providing a recording timing control means for supplying the recording signals to the magnetic head at a different timing for every channel, a plurality of channels can be dealt with simultaneously, for example, one channel for reproducing and another channel for recording. The foregoing arrangement may additionally include the following. An A/D converter and a D/A converter; the former converts analog recording signals into digital recording signals, and the latter converts digital reproducing signals into analog reproducing signals. Using these converters, it is possible to cope with the case in which signals to be exchanged between this apparatus and the exterior must be analog. Therefore digital signals can be recorded and reproduced on and from the magnetic tape. Further, a time axis compressing means for compressing the time axis of the recording signal by 1/m times, and a time axis expanding means for expanding the time axis of the reproducing signal by m times. Some of the foregoing five arrangements need both of the two means, and also to the remaining arrangements, these two means are effective in recording all of information contained in the signals supplied from the exterior. In recording and reproducing digital signal accurately, the apparatus should preferably include means for encoding the digital recording signal for error correction, and means for decoding the digital reproducing signal for error correcting. Further, in recording and reproducing the digital recording signal in code suitable for recording and reproducing on and from the magnetic tape, the apparatus should preferably include means for encoding the digital recording signal for recording, and means for decoding the digital reproducing signal for recording. Finally, for using the magnetic head commonly in recording and reproducing, the apparatus should preferably include a recording/reproducing switching means. The above and other advantages, features and objects of this invention will be manifest to those versed in the art upon making reference to the following detailed description and the accompanying drawings FIG. 1 is a diagram showing the arrangement of magnetic heads in a magnetic recording and reproducing apparatus according to an embodiment; FIG. 2 is a diagram showing a track pattern on the magnetic tape in the embodiment; FIG. 3 is a block diagram showing a circuit construction according to the embodiment; FIG. 4 is a diagram showing the recording of a first channel and the reproducing of a second channel, of recording/reproducing of the magnetic heads in the embodiment; FIG. 5 is a diagram showing the reproducing of the first channel and the recording of the second channel, of the recording/reproducing of the magnetic heads in the embodiment; FIG. 6 is a diagram showing data to be recorded/reproduced and the movement of the magnetic head during the recording of the first channel and the reproducing of the second channel in the embodiment; FIG. 7 is a block diagram showing a magnetic recording and reproducing apparatus according to a second embodiment; FIG. 8 is a diagram showing a track pattern on the magnetic tape during one-channel recording and reproducing in the second embodiment; FIG. 9 is a diagram showing a track pattern on the magnetic tape during two-channel recording and reproducing in the second embodiment; FIG. 10 is a diagram showing a track pattern when operation is shifted from one-channel recording and reproducing to two-channel recording and reproducing in the second embodiment, and also showing the change of feed speed of the magnetic tape; FIG. 11 is a timing diagram showing the operation when it is shifted from one-channel recording and reproducing to two-channel recording and reproducing in the second embodiment; FIG. 12 is a diagram showing a track pattern when operation is shifted from two-channel recording and reproducing to one-channel recording and reproducing in the second embodiment, and also showing the change of feed speed of the magnetic tape; FIG. 13 is a timing diagram showing the operation when it is shifted from two-channel recording and reproducing to one-channel recording and reproducing in the second embodiment; FIG. 14 is a block diagram showing a magnetic recording and reproducing apparatus according to a third embodiment; FIG. 15 is a diagram showing data to be recorded/reproduced and the movement of the magnetic heads in the third embodiment; FIG. 16 is a diagram showing the arrangement of magnetic heads in a magnetic recording and reproducing apparatus according to the prior art; FIG. 17 is a diagram showing a track pattern on the magnetic tape in the prior art; FIG. 18 is a block diagram showing a circuit construction of the prior art; FIG. 19 is a diagram showing data to be recorded and the movement of the magnetic heads when the magnetic tape is fed in the backward or reverse direction in the prior art; FIG. 1 shows the arrangement of magnetic heads in a magnetic recording and reproducing apparatus according to an embodiment. FIG. 2 shows a track pattern in which signals are recorded on a magnetic tape by the magnetic heads. In FIG. 1, the first and second magnetic heads 801-1, 801-2 are disposed on the peripheral surface of a rotary drum 802 and are angularly spaced from each other by 180°. Of tracks constituting the track pattern of FIG. 2, a track 811-1 is a track on which the first magnetic head 801-1 scans during the first rotation of the rotary drum 802, a track 811-2 is a track on which the second magnetic head 801-2 scans during first rotation of the rotary drum 802, a track 811-3 is a track on which the first magnetic head 801-1 scans during the second rotation of the rotary drum 802, and a track 811-4 is a track on which the second magnetic head 801-2 scans during the second rotation of the rotary drum 802. FIG. 3 is a block diagram showing a signal processing system in which when the magnetic heads are arranged as shown in FIG. 1 and when the tracks are formed in the pattern shown in FIG. 2, two-channel video signals can be reproduced while being digitally recorded on the tracks. A reproducing head amplifier 843 amplifies reproducing signals from the magnetic heads 801-1, 801-2. A demodulator 854 decodes, for recording, in the manner reverse to the encoding, for recording, by a modulator 853. A decoder 855 performs error correction and detection by decoding the data to which error correcting codes were added by an encoder 852. A memory 901 is used in decoding by the decoder 855. A D/A converter 856 analogizes the reproducing video data in which errors have been corrected. An LPF 857 restricts the reproducing video signals to a video signal band. A head changeover switch 833 changeovers from the recording head amplifier 842 to the reproducing head amplifier 843 and vice versa for connection to the magnetic heads 801-1, 801-2, based on the head changeover signal. The video signals of the first and second channels are inputted to the respective input terminals 884-1, 884-2 during recording. The video signals of the first and second channels are outputted from the respective output terminal 887-1, 887-2 during reproducing. A video signal changeover switch 902 changesover the input/output signals of the first and second channels based on the video signal changeover signals. FIGS. 4 and 5 show the manner in which the first and second magnetic heads 801-1, 801-2 are switched by the head changeover signal. Each magnetic head 801-1, 801-2 records (W) at the high level of the head changeover signal and reproduces (R) at the low level. Each of the hatched portions on a line, which show the posture of the individual magnetic head 801-1, 801-2, represents a magnetic tape tracing period. FIG. 6 shows data to be recorded/reproduced and the movement of the magnetic head during the recording of the first channel and the reproducing of the second channel. In FIG. 6, the recording data obtained by digitizing the video signal of one channel are represented by W-DATAi (i = 0, 1, ...); and the recording compressed data obtained by compressing the time axis of the recording data are represented by WDi (i = 1, 0, ...). Likewise, the reproducing compressed data obtained by reproducing the second channel data are represented by R-DATAi (i = 1, 2, ...); and the reproducing data obtained by expanding the time axis of the reproducing compressed data are represented by RDi (i = 1, 2, ...). Further, each of the hatched portions on a line, which indicate the posture of individual magnetic heads 801-1, 801-2, shows a magnetic tape tracing period. In operation, the rotary drum 802, on which a pair of magnetic heads 801-1, 801-2 is supported with an angular space by 180°, is rotated at a rotational frequency two times higher than conventional, and the magnetic tape 810 is fed at a speed two times higher than conventional. On the magnetic tape 810, four tracks are thereby formed/scanned during two rotations of the rotary drum 802. The rotary drum 802, which rotates at a speed two times higher than conventional, makes two rotations during the period needed for one rotation of the rotary drum in the prior art. Therefore, tracks are formed/scanned at the same speed as conventional. During the first rotation of the rotary drum 802, the first magnetic head 801-1 scans the track 811-1, and the second magnetic head 801-2 scans the track 811-2. During the next rotation of the rotary drum 802, the first magnetic head 801-1 scans track 811-3, and the second magnetic head 801-2 scans the track 811-4. In these four tracks, the tracks 811-1, 811-3 are associated with one channel, and the tracks 811-2, 811-4 are associated with the other channel. The mode of operation in which recording of one channel and reproducing of the other channel are performed simultaneously will now be described with reference to FIG. 3. Firstly, in the recording signal processing system, the video signal changeover switch 902 is operable in response to the inputting of the video signal changeover signal. As a result, the input terminal 884-1 of the first channel video signal or the input terminal 884-2 of the second channel video signal is selected, and the video signal to be inputted to the selected terminal is inputted to the LPF 850. The video signal inputted to the LPF 850 is restricted in band by the LPF 850 likewise the prior art of FIG. 18 and is then digitized by the A/D converter 851. The digitized video signal is encoded by the encoder 852 with use of the memory 838, is encoded, for recording, by the modulator 853, and is recorded on the magnetic tape 810. Further, the signal encoded for recording is recorded by the first magnetic head 801-1 or the second magnetic 801-2 via the head changeover switch. At that time, the head changeover switch 833 is turned to the side of the recording head amplifier 842. In the reproducing signal processing system, the reproducing signal reproduced from the first magnetic head 801-1 or the second magnetic head 801-2 is decoded, for recording, by the demodulator 854 via the head changeover switch 833. Using the memory 901, error correction, detection and interpolation are made by the decoder 855. At that time, the head changeover switch 855 is turned to the side of the reproducing head amplifier 843. Subsequently, the reproducing video signal analogized by the D/A converter 856 is band-restricted by the LPF 857. At that time, by the action of the video signal changeover switch 902, the output terminal 887-1 of the first channel video signal or the output terminal 887-2 of the second channel video signal is selected, and the reproducing video signal is outputted to the selected output terminal. Here, to the head changeover switch 833, the head changeover signal such as shown in FIGS. 4 and 5 is supplied. Thereby, the recording signal is supplied to the first magnetic head 801-1 and the second magnetic head 801-2, or the reproducing signal is taken out or switched from these magnetic heads 801-1, 801-2. Namely, recording at the high level of the head changeover signal or reproducing at the low level is selected. FIG. 4 shows a head changeover signal in recording the first channel by the first magnetic head 801-1 and in reproducing the second channel by the second magnetic head 801-2. FIG. 5 shows a head changeover signal in reproducing the first channel by the first magnetic head 801-1 and in recording the second channel by the second magnetic head 801-2. Here, the case in which recording of the first channel video signal and reproducing of the second channel video signal are performed simultaneously will be described. In FIG. 6, the first channel data digitized by the A/D converter 851 are recording data divided into blocks W-DATA1, W-DATA2 ..., for example, in units of fields. The recording data are encoded by adding an error correcting code by the encoder 852 and are time-compressed simultaneously, thus becoming recording compressed data WD0, WD1, WD2 .... Then, as the result of changeover of the head changeover switch 833 by the head changeover signal, the recording compressed data are recorded on the tracks 811-1, 811-3 while the first magnetic head 801-1 is scanning the magnetic tape 810. Meanwhile, in synchronism with the termination of scanning of the magnetic tape 810 by the first magnetic head 801-1, the head changeover switch 833 is switched to the side of the reproducing head amplifier by the head changeover signal. Until the head changeover switch 833 is switched again, namely, until the second magnetic head 801-2 scans the track 811-2 or 811-4 on the magnetic tape 810 completely, the second magnetic head 801-2 reproduces the tracks 811-2, 811-4 on which the second channel video signal is recorded. This reproducing signal, which is time-compressed during recording, is reproduced as reproducing compressed data RD1, RD2 .... Subsequently, the reproducing compressed data are decoded by the decoder 855 to correct the error and are time-expanded simultaneously, thus becoming reproducing data divided into blocks R-DATA0, R-DATA1, ..., in units of fields. The reproducing data are analogized by the D/A converter 856 and are reproduced and outputted as the second channel video signal. As mentioned above, during the period one of the magnetic heads 801-1, 801-2 scans the magnetic tape 810 two times as the rotary drum 802 makes two rotations during the period of one frame of the video signal, the data of one frame video signal of one channel are time-compressed and recorded for every field. As a result, recording one channel and reproducing the other channel can be performed simultaneously. In this embodiment, the tracks 811-1, 811-3 are associated with one channel, and the tracks 811-2, 811-4 are associated with the other channel. Alternatively, the tracks 811-1, 811-2 may be associated with one channel, and the tracks 811-3, 811-4 may be associated with the other channel, giving the same result as this embodiment. Further, in this embodiment, one cycle of information is defined as one frame, and one cycle of information is recorded on two tracks. Alternatively, one cycle of information may be one field, or one field plus an integral number of frames. The number of tracks on and from which one cycle of information is to be recorded and reproduced should not be limited to any specific number. As mentioned above, since rotary drum makes two or more rotations within the period of one cycle of information to increase the number of tracks to be scanned within the same period, it is possible to record and reproduce the data in terms of time. Consequently, with the construction for only one channel, it is possible to record one channel and, at the same time, to reproduce the other channel. There are only a few modifications required to a one-channel recording and reproducing apparatus, thus lowering the rate of production. FIG. 7 shows a digital recording and reproducing apparatus according to a second embodiment. In FIG. 7, a time compressing circuit 1097 compresses the time axis of every block of data obtained by digitizing first and second channel recording video signals. An ID generating circuit 1103 generates, independently of video data, an identification data (hereinafter called "ID") signal to be recorded on one track. An ID detecting circuit 1104 separates an ID signal from reproducing video signal data. A time expanding circuit 1098 expands the time axis of every block of data after decoded at the same rate as that of the time axis compression by a time compressing circuit 1097. A mechanism control circuit 1014 controls the feed speed of the tape. A recording and reproducing mode changeover signal is a signal for switching the mode from the recording mode to the reproducing mode and vice versa. The ID detecting circuit 1104 produces a signal process changeover signal by the detected ID signal to changeover the signal processing system by this signal process changeover signal. Further, the ID detecting circuit 1104 produces a mechanism changeover signal by the detected ID signal and supplies the same signal to the mechanism control circuit 1014 to changeover the feed speed of the magnetic tape. FIG. 8 shows a track pattern during one-channel recording and reproducing mode in this embodiment. The track 1011-1 is a track on which a magnetic head 1001-1 records during the first rotation of a rotary drum 1002, a track 1011-2 is a track on which a magnetic head 1001-2 scans during the first rotation of the rotary drum 1002, a track 1011-3 is a track on which the magnetic 1001-1 records during the second rotation of the rotary drum 1002, and a track 1011-4 is a track the magnetic head 1001-2 scans during the second rotation of the rotary drum 1011-4. FIG. 9 shows a track pattern during two-channel recording and reproducing mode. FIG. 10 is a diagram showing a track pattern when operation is shifted from one-channel recording and reproducing to two-channel recording and reproducing, and also showing the change of feed speed of the magnetic tape. A track 1011-5 is scanned soon after switching the feed speed of the tape, and a track 1011-6 on which recording and reproducing are performed during the period of switching the feed speed of the tape. FIG. 11 is a timing diagram showing the operation when it is shifted from one-channel recording and reproducing to two-channel recording and reproducing. The scanning periods of the individual magnetic heads 1001-1, 1001-2 is represented by hatched portions. The data of each channel to be recorded and reproduced are represented by a box right under the individual hatched portion. The ID signals to be recorded and detected are designated by A, B and C. The recording and reproducing mode changeover signal corresponds at the low level to one-channel recording and reproducing mode and at the high level to two-channel recording and reproducing mode. A feed speed changeover signal corresponds at the low level to an ordinary speed and at the high level to a double speed. Further, also shown in FIG. 11 are the feed speed of the magnetic tape, the feed speed changeover completion signal and the signal processing system changeover signal. The signal processing system changeover signal. The signal processing system changeover signal corresponds at the low level to one-channel recording and reproducing and at the high level to two-channel recording and reproducing. FIG. 12 is, reverse to FIG. 10, a diagram showing a track pattern when operation is shifted from two-channel recording and reproducing to one-channel recording and reproducing, and also showing the change of feed speed of the magnetic tape. FIG 13 is, reverse to FIG. 11, a timing diagram showing the operation when it is shifted from two-channel recording and reproducing to one-channel recording and reproducing. In operation, a pair of magnetic heads 1001-1, 1001-2 are supported on the peripheral surface of the rotary drum 1002 and are angularly spaced from each other by 180°. During two-channel recording and reproducing in this embodiment, the rotary drum 1002 is rotated at a speed two times higher than conventional. Therefore, during the period needed for two rotations of the rotary drum 1002, the four tracks 1011-1 through 1011-4 shown in FIG. 14 are formed/scanned. Specifically, within the time needed for one rotation of the prior art rotary drum (within the period of one frame), the rotary drum 1002 of this embodiment makes two rotations. During the first rotation of the rotary drum 1002, the magnetic ahead 1001-1 scans the track 1011-1, and the magnetic head 1001-2 scans the track 1011-2. During the next rotation of the rotary drum 1002, the magnetic ahead 1001-1 scans the track 1011-3, and the magnetic head 1001-2 scans the track 1011-4. During recording of only the first channel, only the tracks 1011-1, 1011-3 indicated in solid lines in FIG. 13 are recorded by the magnetic head 1001-1. The one-channel recording and reproducing mode will now be described. Like the prior art, the first channel recording video signal is band-restricted by an LPF 1050-1 and is digitized by an A/D converter 1051-1. The data are divided into blocks, for example, in units of fields, and the time axis of the data is compressed, for every block, by 1/2 or less times by the time compressing circuit 1097. The time-compressed data of every block are encoded by an encoder 1052 like the prior art, using the memory 1038. And the same data are composed with an ID signal from the ID generating circuit 1103. The composed data are further encoded, for recording, by the modulator 1053. The recording data here are intermittent data for every period of one field and are recorded on the tracks 1011-1, 1011-3 of FIG. 8 via the recording amplifier 1042. Therefore, only during the scanning period of the magnetic head 1001-1, recording on the magnetic tape 1010 is performed, and during the scanning period of the magnetic head 1001-2, no recording is performed. During reproducing, the data to be reproduced during the scanning period of the magnetic head 1001-1 decoded, for recording, by a decoder 1054 via a reproducing head amplifier 1043. An ID detecting circuit 1104 separates ID signal and reproducing video signal data composed during recording. The separated reproducing video data are error-corrected, error-detected and interpolated by an decoder 1055, using the memory 1011. The time expanding circuit 1098 expands the time axis of the reproducing video data at the same rate as the time axis compression by the time compressing circuit 1097 during recording. Here the reproducing video data, in the form of a succession of blocks, are converted into an analog signal by a D/A converter 1056-1 and are band-restricted by an LPF 1057-1. Thus a first channel reproducing video signal has been obtained. The two-channel recording and reproducing mode in which the first and second channels are recorded and reproduced simultaneously. In this mode, the magnetic tape 1010 is fed at a speed two times higher than that of the one-channel recording and reproducing mode. Therefore, like during the one-channel recording and reproducing, four tracks of the magnetic tape 1010 are scanned during two rotations of the rotary drum 1002. However, in this mode, the individual tracks do not overlap one another to form a track pattern shown in FIG. 9. During recording, the magnetic heads 1001-1, 1001-2 record four tracks within the period of one frame. In the signal processing system, the first and second channel recording video signals are band-restricted by the respective LPFs 1050-1, 1050-2. The band-restricted signals are digitized respectively by A/D converters 1051-1, 1051-2 and are time-compressed by the time compressing circuit 1097. This time compression here is performed in every block for both channels, and the compressed data of two channels are arranged alternately in blocks. As a result, a succession of data has been produced. The successive data are encoded, for error correction, by an encoder 1052 and are encoded, for recording, by a modulator 1053 after composed with ID signals. The data encoded for recording are recorded on the magnetic tape 1010 via a recording head amplifier 1042 and a head changeover switch 1033. At that time, the magnetic head 1001-1 records first channel recording data, and the magnetic head 1001-2 records second channel recording data. During reproducing, the magnetic heads 1001-1, 1001-2 reproduce data of the respective channels. At that time, like the one-channel reproducing mode, decoding by a demodulator 1054 for recording, ID detection by an ID detecting circuit 1104, error correction by a decoder 1055, and interpolation. Further, in the time expanding circuit 1098, the reproducing data of two channels are separated for every block and are respectively time-expanded, thus obtaining the reproducing video data of the first and second channels. The reproducing video data of the individual channels are converted into analog signals by the respective D/A converters 1056-1, 1056-2 and are band-restricted by the respective LPFs 1057-1, 1057-2. As a result, first and second channel reproducing video signals have been obtained. As mentioned above, in the one-channel recording and reproducing mode, signal processing after time compression during recording until time expansion during reproducing is intermittent processing of compressed data of one channel. In the two-channel recording and reproducing mode, the compressed data of two channels are successively processed. An ID signal to be added at an ID generating circuit 1103 includes data which discriminate these two kinds of recording and reproducing modes. The data are recorded on the magnetic tape as ID signals during recording of each mode. Here, for example, the ID signal is recorded at two positions on opposite end of the track as A in the one-channel recording and reproducing mode and as B in the two-channel recording and reproducing mode. The case in which one of one-channel and two-channel recording and reproducing modes is switched to the other mode during operation in the former mode. Firstly, the case in which the one-channel recording and reproducing mode is switched to the two-channel recording and reproducing mode during operation in the first mode. When a recording and reproducing mode changeover signal is generated during recording of one channel, the mechanism control circuit 1014 changeovers, in response to this signal, the feed speed of the magnetic tape from a one-fold speed to a two-fold speed. However, because of followability of the motor, the feed speed of the magnetic tape 1010 cannot be instantaneously increased to a two-fold speed. For this reason, when the feed speed of the magnetic tape is detected as actually having increased to a two-fold speed, the signal processing system should necessarily be switched to the two-channel recording mode. FIG. 10 shows a track pattern recorded on the magnetic tape 1010 during the period needed for shifting the feed speed of the magnetic tape, namely, the mode changeover period. During this period, no track can be formed. To this end, for distinguishing this track from an ordinary track, an ID signal C, independent from A and B indicating two kinds of modes, is used as the ID signal of the track 1011-6 during this period. Further, to detect the feed speed switching period reliably, C is also recorded on an ID signal on the trailing end of the track 1011-5 right before switching the feed speed of the magnetic tape is started. In operation, as shown in FIG. 11, firstly when the recording mode changeover signal rises, an ID signal C is recorded at the trailing end of the succeeding track formed as the magnetic head 1011-1 scans. At the timing of switching from the magnetic head 1001-1 to the magnetic head 1001-2, the feed speed of the magnetic tape is started switching. The the mechanism control circuit 1014 is detected that the tape is being fed at a two-fold speed, whereupon the signal processing system will be shifted to the two-channel recording mode at the timing of switching from the magnetic head 1001-2 to the magnetic head 1001-1. For reproducing the track thus recorded, in response to the recording and reproducing mode changeover signal during one-channel reproducing, or in response to the detection of shifting from the ID signal A to the ID signal C by the ID detecting circuit 1104, both the feed speed of the magnetic tape and the signal processing system are switched to the two-channel reproducing mode at the same timing as that during recording. Then, the case in which the two-channel recording and reproducing mode is switched to the one-channel recording and reproducing mode during operation in the former mode will be described. During recording, in response to the recording and reproducing mode changeover signal, the mechanism control circuit 1014 switches the operation of the drive system so as to changeover the feed speed of the magnetic tape from a two-fold speed to a one-fold speed. Also regarding the signal processing system, in response to the recording and reproducing mode changeover signal, the two-channel recording mode is switched to the one-channel recording mode. The resulting recording track pattern is shown in FIG. 12. The ID signal here also will be regarded as C at the trailing end of the track 1011-6·during the feed speed switching and of the track 1011-5 right before the feed speed switching is started. In operation, as shown in FIG. 13, during recording, when the recording and reproducing mode changeover signal rises, an ID signal at the trailing end of the succeeding track to be recorded by scanning by the magnetic head 1001-1 will be recorded as C. At the timing of switching from the magnetic head 1001-1 to the magnetic ahead 1001-2, switching the feed speed of the magnetic tape will be started, at which time the signal processing system is the one-channel recording mode. For reproducing, when the recording and reproducing mode changeover signal rises during two-channel reproducing, or when the change of the ID signal from B to C is detected, both the feed speed of the magnetic tape and the signal processing system will be switched to the one-channel reproducing mode at the same timing as that during recording. In this embodiment, the ID signal is recorded on a helical track. The ID signal may be recorded and reproduced on and from a linear track. Further, in this embodiment, one cycle of information is defined as one frame, and one cycle of information is recorded on two tracks. Alternatively, one cycle of information may be one field, or one field plus an integral number of frames. The number of tracks on and from which one cycle of information is to be recorded and reproduced should not be limited to any specific number. As mentioned above, partly since the rotary drum makes two or more rotations during the period of one cycle of information, and partly since the feed speed of the magnetic tape is switchable, it is possible to switch the operation mode from one-channel recording and reproducing mode to two-channel recording and reproducing mode and vice versa even while the magnetic tape is being fed. FIG. 14 shows a recording signal processing system according to a third embodiment. This recording signal processing system digitally records two-channel video signals simultaneously. An encoder 1252 is operable at a higher rate than conventional. A buffer memory 1238 is capable of writing and reading at high rate to perform high-speed encoding. Responsive to this, a modulator 1253 also is capable of encoding at a higher rate than conventional. Also a head amplifier 1242, covers a higher band than conventional. Further, a buffer memory 1305 is used for synchronizing two-channel video digital data. FIG. 15 shows the data distribution to be recorded/reproduced and the movement of the magnetic heads. The data DATA1-1, DATA2-1, ... represent the recording data to be outputted from the modulator 1253. Further, each of the hatched portions on a line, which indicate the movement of each magnetic head, represents a period of tracing the magnetic tape. In operation, A pair of magnetic heads 1201-1, 1201-2 are supported on the peripheral surface of a rotary drum 1202 and are angularly spaced from each other by 180°. When the rotary drum 1202 is rotated at a speed two times higher than conventional and the magnetic tape 1210 is fed at two-fold speed, a track will be formed on the magnetic tape 1210 in the same pattern as that in the second embodiment (FIG. 9). Specifically, the first and second channel video signals are band-restricted by the respective LPFs 1250-1, 1250-2 and are digitized by the respective A/D converters 1251-1, 1251-2. Of these two-channel video data, the second channel video data are shifted by 1/2 field by the buffer memory 1305. As a result, the preceding first channel data are encoded prior to the remaining data by the encoder 1252. However, encoding here is performed at a processing rate two or more times higher than conventional by a buffer memory 1238. Therefore, partly since the period of time needed for encoding data of one frame of the preceding channel requires only a 1/2 field period, and partly since encoding of data of one field of the other channel also requires only a 1/2 field period, the former should be associated with 1/2 field and the latter should be associated with 1/2 field. The digital data of one field of high data rate including both channels are encoded, for recording, at high speed, by the modulator 1253. The recording data arrangement will therefore be such as shown in FIG. 15. Specifically, during the first rotation of the rotary drum 1202, the data of one field of the first channel DATA1-1 are recorded on a track 1-A by the magnetic head 1201-1, and then the data of one field of the second channel DATA2-1 are recorded on a track 1-B by the magnetic head 1201-2. During the second rotation of the rotary drum 1202, the data of one succeeding field of the first channel DATA1-2 are recorded on a track 2-A by the magnetic head 1201-1, and then the data of one succeeding field of the second channel DATA2-2 are recorded on a track 2-B by the magnetic head 1201-2. Therefore, the magnetic head 1201-1 records the first channel, while the magnetic head 1201-2 records the second channel. Thus within one field period, the data of one field of both channels can be recorded simultaneously. Also during recording, by separating rows of data for individual channels, it is possible to reproduce both channels. As mentioned above, according to this embodiment, by rotating the rotary drum 1202 at a speed two or more higher than conventional, recording/reproducing of information of two channels is possible by a pair of magnetic heads 1201-1, 1201-2 angularly spaced from each other by 180°. Further, since the encoder 1252 and the modulator 1253 can be composed only elements of one channel, only a few modifications are necessary to manufacture from the starting one-channel magnetic recording and reproducing apparatus, thus realizing a two-channel magnetic recording and reproducing apparatus inexpensively. In this embodiment, the first channel is recorded by the magnetic head 1201-1, and the second channel is recorded by the magnetic head 1202-2. Alternatively, the data of one field of the first channel may be recorded during the first rotation of the rotary drum 1202, and the data of one field of the second channel may be recorded during the second rotation of the rotary drum 1202. Further, in this embodiment, one cycle of information is defined as one frame, and one cycle of information is recorded on two tracks. Alternatively, one cycle of information may be one field, or one field plus an integral number of frames. The number of tracks on and from which one cycle of information is to be recorded and reproduced should not be limited to any specific number. Assuming that 2N or more tracks are scanned during the period of one cycle scanning of the first information and that the first information and the second information are recorded/reproduced simultaneously, it is possible to record/reproduce two video signals simultaneously in two channels, without adding any magnetic head and increasing the size of the circuit. Accordingly a two-channel magnetic recording and reproducing apparatus can be achieved with low cost.

Claims: A magnetic recording and reproducing apparatus for simultaneous processing of a plurality (n) (n stands for an integer larger than 1 and equal to or smaller than m) of channels, comprising (a) a rotary drum (1002) having an outer periphery which is frictionally engageable with a magnetic tape (1010) in. such a manner that the axis of rotation of said rotary drum is disposed at a predetermined angle with respect to the moving direction of the magnetic tape; (b) m (m stands for an integer larger than 1) number of magnetic heads (1001-1, 1001-2) disposed on the outer periphery of said rotary drum for performing scanning on the magnetic tape so as to record on a predetermined-width track on the magnetic tape a recording signal to be applied during recording, and so as to pick up a reproducing signal from the predetermined-width track on the magnetic tape during reproducing; (c) tape speed control means for controlling the speed of feed of the tape to be a multiple (n) of one channel feed speed during n channel recording/reproducing characterised by (d) a track scanning means for causing said magnetic head to scan at a multiple n of the one channel scan frequency during n channel recording/reproducing for one cycle of information to be recorded on the magnetic tape; and (e) a channel composing and separating means (902 1097, 1098) for selecting between the n channels and for composing recording signals of the individual channels during recording and for selecting between the n channels and for separating reproducing signals into the individual channels during reproducing. A magnetic recording and reproducing apparatus according to claim 1, wherein said channel composing and separating means further includes an identification code adding means (1103) for adding to a recording signal an identification code indicating the speed of feed of the magnetic tape and causing said magnetic head to record the identification code in a predetermined portion of the track on the magnetic tape during recording, and an identification code separating means (1104) for separating and detecting an identification code from a reproducing signal and instructing said tape speed control means to control the feed speed of the magnetic tape to a target feed speed during reproducing. A magnetic recording and reproducing apparatus according to claim 2, wherein said identification code adding means adds to a recording signal a transitional identification code during transition of switching of the feed speed of the magnetic tape, while said identification code separating means instructs the feed speed of the magnetic tape to be changed in response to the detection of the transitional identification code. A magnetic recording and reproducing apparatus according to claim 1, further comprising a recording timing control means for supplying recording signals to said magnetic head at different timings for respective channels. A magnetic recording and reproducing apparatus according to claim 1, further comprising: an A/D converter (1051) for converting an analog recording signal into a digital recording signal and for supplying the latter to said magnetic head; and a D/A converter (1056) for converting a digital reproducing signal, which is picked up by said magnetic head, into an analog reproducing signal. A magnetic recording and reproducing apparatus according to claim 1, further comprising: a time axis compressing means for compressing the time axis of the recording signal by 1/m times and for supplying the compressed recording signal to said magnetic head; and a time axis expanding means for expanding the time axis of the reproducing signal by m times. A magnetic recording and reproducing apparatus according to claim 1, further comprising: means (1052) for encoding the digital recording signal for error correction; and means (1055) for decoding the digital reproducing signal for error correction. A magnetic recording and reproducing apparatus according to claim 1, further comprising: means (1052) for encoding the digital recording signal for recording; and means (1055) for decoding the digital reproducing signal for recording. A magnetic recording and reproducing apparatus according to claim 2, further comprising a recording/reproducing switching means (1033) for supplying a recording signal to said magnetic head during recording and for taking out a recording signal from said magnetic head during reproducing.

Inventors: HONGO KIMITOSHI, ONISHI KEN, TAKADA YUKARI, HONGO, KIMITOSHI, ONISHI, KEN, TAKADA, YUKARI, HONGO, KIMITOSHI, C/O MITSUBISHI DENKI K. K., ONISHI, KEN, C/O MITSUBISHI DENKI K. K., TAKADA, YUKARI, C/O MITSUBISHI DENKI K. K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: G11B5
IPC codes: G11B15, H04N5, H04N9, G11B20, G11B27, G11B5