JPH0551983B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rotary head type playback device suitable for application to, for example, a rotary head type video tape recorder, PCM tape recorder, etc.

[Summary of the invention]

The present invention relates to a rotary head type playback device suitable for application to, for example, a rotary head type video tape recorder, a PCM tape recorder, etc., in which a block is configured for each digital information signal of a predetermined length, and a block address signal is added to each block. a rotary head that scans a plurality of times, for example twice, in a recording scan in which a predetermined number of blocks are recorded; and a memory in which a digital signal reproduced by the rotary head is written in accordance with the block address signal;
By reading out the digital signals written in this memory in the same order as when they were recorded, the reproduced digital information signal has the same time sequence as when it was recorded. This allows playback without tracking.

[Problems to be solved by conventional technology and invention]

A VTR (video tape recorder) is well known as a rotary head type playback device. In conventional VTRs, the track width is set to several tens of micrometers or less for high-density recording, and a control signal recorded in the longitudinal direction of the side edge of the magnetic tape is reproduced along with the recording signal, and the rotation is controlled by this control signal. The rotation of the head and capstan is controlled, and a tracking servo is applied so that the scanning locus of the head during reproduction matches the recording track. Also,
In high-end VTRs, the rotary head is movable not only by control signals but also by a piezoelectric element, and changes in the envelope of the reproduced signal obtained by wobbling the rotary head, or mutual changes between several recording tracks, are used. Crosstalk components of pilot signals of different frequencies are used to move the rotary head to ensure correct tracking.

Further, as a prerequisite for performing regular tracking, it is necessary that the tape running path including the tape guide drum has high mechanical precision and that the tape guide drum has high hardness.

These high-precision tracking servos, high machining precision, etc. are obstacles to lowering the cost of rotary head type playback devices.

The object of the present invention is to realize a rotary head type reproducing device that does not require any high-precision machining, high-hardness cylinders, high-precision servos, etc. required for tracking. Furthermore, the present invention provides that even when a digital information signal is continuous, unlike an analog information signal,
The present invention aims to provide a rotary head type device that reproduces digital information signals by paying attention to the fact that the seam does not become discontinuous.

[Means to solve the problem]

The rotary head type reproducing apparatus of the present invention configures a block for each digital information signal of a predetermined length as shown in FIG. A rotary head 2 that scans a plurality of times, for example, twice, and a memory 18 in which the digital signal reproduced by the rotary head 2 is written in accordance with the block address signal are provided, and the digital signal written in the memory 18 is recorded. The data are made continuous by reading them in the same order as the time.

[Effect]

According to the present invention, the rotary head 2 is scanned a plurality of times, for example twice, over a recording track in which a predetermined number of blocks to which address signals have been added are recorded, and the reproduced digital signal is converted into the reproduced address signal. Therefore, since the data is written in the memory 18 and the digital signals written in the memory 18 are read out in the same order as in recording, reproduction can be performed without performing highly accurate tracking.

〔Example〕

Hereinafter, an embodiment of the rotary head type reproducing apparatus of the present invention will be described with reference to the drawings. This example is an example applied to a rotating head type PCM tape recorder.

In FIG. 2, 1a and 1b indicate an upper drum and a lower drum, respectively, for guiding the magnetic tape, and a rotating head 2 slightly protrudes from between these two drums.
A magnetic tape 3 running while being wound obliquely over 360 degrees on both sides of drums 1a and 1b is brought into sliding contact with a rotary head 2. As shown in FIG. 3, inclined recording tracks T _o-1 , T _o , T _o+1 , . . . are sequentially formed on the magnetic tape 3 .
In this example, the recording tracks T _o-1 , T _o , T _o+1 ,...
The track width Wt is selected to be equal to the card bandwidth Wg between adjacent tracks.

In FIG. 1, an analog signal to be recorded, such as an audio signal, is supplied to an input terminal indicated by 4,
The A/D converter 5 converts the signal into an audio PCM signal. This audio PCM signal is supplied to the encoder 6, where a synchronization signal, error correction code, and error detection code are added. FIG. 4 shows the code structure of recording data obtained from the output of the encoder 6. A synchronization signal, a block address signal, and a CRC code for error detection are added to data consisting of a plurality of samples of audio PCM signals or error correction codes. As the error correction code, a parity code, adjacent code, etc. can be used.
Also, interleaving may be used together. The block address signal is as described below.
This is used to individually distinguish blocks in a series of playback data input to the TBC memory, and can use simple incremental code signals, combinations of multiple types of addresses, etc.
The CRC code is designed to detect the presence or absence of errors in both the block address signal and data.

The output of the encoder 6 is supplied to a modulator 7 and converted into a code format suitable for recording and reproduction.
Various modulation methods such as NRZI, 3PM, MFM, etc. can be used. A recording signal obtained from the output of the modulator 7 is supplied to the rotary head 2 via a recording amplifier 8, a recording terminal 10r of a recording/reproducing switch 9, and a rotary transformer (not shown).

During reproduction, the rotational speed of the rotary head 2 is set to be higher, for example twice, than during recording. In other words, the rotary head 2 scans the magnetic tape 3 twice while the magnetic tape 3 is fed one track. In this way, since the number of scans during playback is larger than the number of scans during recording, the playback scan locus pitch is smaller than the track pitch, and even if no tracking is performed, each of all recorded tracks can be scanned one line at a time. The reproduction scanning trajectory described above must be passed through.

The playback output of the rotary head 2 is taken out to the playback side terminal 10p of the recording/playback switch 9, and is sent to the playback amplifier 11.
is supplied to the detector 12 via. The detector 12 shapes the waveform of the reproduced signal into a pulse signal. The output of this detector 12 is supplied to a clock extraction circuit 13, and a clock pulse synchronized with reproduced data is extracted. The output of this clock extraction circuit 13 is supplied to a demodulation circuit 14, and reproduced data having the same code structure as the recorded data is obtained.

This reproduced data is supplied to a delay circuit 15, a synchronous separation circuit 16, and a CRC checker 17. CRC
The checker 17 uses a synchronization signal to detect the presence or absence of errors in each block of reproduced data and block address signals using a CRC code.
An error flag indicating the presence or absence of an error is generated for each block in the output. The error flag becomes "1" when an error is detected, and becomes "0" when no error is detected. The delay circuit 15 delays the reproduced data and block address signal by the time required for error detection by the CRC checker 17.

The above-mentioned playback data, block address signal, and error flag are processed by the time base collector (hereinafter referred to as
(abbreviated as TBC) 18. TBC18
consists of a memory (RAM) and its peripheral circuits.Basically, the reproduced data is written to the memory by a clock synchronized with the reproduced data, and the memory is written by a reference clock from the timing generation circuit 19. It is configured to read data from and remove time axis fluctuations. Writing to the memory of the TBC 18 is performed using an address based on a block address signal, and writing of data determined to have an error by an error flag is prohibited. As mentioned above, the error flag indicates not only the data but also the presence or absence of an error in the block address signal, so if there is an error, writing is prohibited to prevent writing to the wrong address. be made into In addition, if writing is prohibited, previously written data remains in the corresponding address, so in order to prevent this from being read as correct data, it is necessary to ensure that the data at that address is error data. Writes an error flag indicating.
This error flag is written immediately after reading correct data. Reading of the memory of the TBC 18 is performed sequentially in a predetermined order, and a data series and an error flag indicating the presence or absence of an error for each block are obtained as output and supplied to the decoder 20.

The decoder 20 corrects data determined to contain air using an error correction code, and performs correction by replacing uncorrectable data with interpolated data. The interpolated data is, for example, the average value of correct data located before and after. Output data from this decoder 20 is supplied to a D/A converter 21, and a reproduced audio signal is taken out at an output terminal 22.

In one embodiment of the invention described above, the track width Wt
and the guard band width Wg are equal, and the number of scans during playback is twice the number of scans during recording, so the recording tracks T _o-1 , T _o , T _o+1 and the playback scan trajectory N ₁ , N ₂ , N ₃ , N ₄ , and N ₅ are shown in Figure 5A.
It will be as shown below. When the rotary head 2 first scans in the direction of the arrow, a scanning trajectory _N1 passing through the recording tracks T _o-1 and T _o is drawn, and the reproduced signal shown in FIG. 5B is
S ₁ is obtained. The reproduced signal has an envelope approximately proportional to the area of the region where the recording track and the scanning locus overlap. Below, the second scanning trajectory N ₂ ,
Every time the third scanning trajectory N ₃ and the fourth scanning trajectory N ₄ are drawn, reproduction signals S ₂ , S ₃ , and S ₄ are generated in sequence. Focusing on the recording track _T0 , the reproduction output from this recording track _T0 is as shown by the solid line in FIG. 5B. The envelopes of the reproduced signals S ₁ and S ₃ reach their maximum values at timings t ₂ and t ₄ ,
The envelopes of the reproduced signals S ₂ and S ₄ reach their maximum values at timings t ₁ and t ₃ . Such a reproduced signal S ₁ ~
_S4 is supplied to the above-mentioned regeneration system and processed,
When the level of the reproduced signals S ₁ to _{S 4} becomes less than a predetermined value, for example, less than 1/3 of the maximum value, the S/N ratio deteriorates, and the waveform shaping may not be performed correctly by the detector 12. Therefore, the reproduced signals S ₁ to S ₄ and the corresponding reproduced data DT ₁ to DT ₄ are, as shown in FIG. Become. However, if we talk about the recording track T _o that we are focusing on, the playback signal S ₁
The data obtained in the interval from t ₃ to t ₄ in the middle and the interval from t ₃ to _{t 4} in the reproduced signal S ₂ are the same,
Similarly, the interval from t ₂ to _{t 3} in the reproduced signal S ₂ and the reproduced signal
Data and reproduced signal obtained in the interval from t ₂ to t ₃ during S ₃
The data obtained in the period from _t1 to _t2 in _S3 and the period from _t1 to _t2 in the reproduced signal _S4 are the same. Due to such duplication of playback data, even if the playback data includes an invalid data section, the data in that part will be played back in the next scan, so there will be no problem. . Also, the fifth
In Figure C, the shaded area is the recording track.
It shows the interval where the same data is obtained overlappingly among the data of T _o . Of course, the recording track T _o
The reproduction data of other recording tracks is also the same as described above.

In this way, one recording track contains either the original audio PCM signal or the audio PCM signal regularly rearranged by interleaving.
Although the signal is recorded, the time series of the reproduced data is different from that at the time of recording. However, when writing playback data to the memory of the TBC 18 as described above, writing is performed at an address determined by the block address signal added to each block of playback data, and reading is performed using the addresses in the same order as when recording. Since this is done by specifying
The time series of the output data of the TBC 18 is the same as that at the time of recording.

In the embodiment described above, the number of revolutions of the rotary head 2 during reproduction is larger than that during recording, for example twice, but the number of traces during reproduction can be made larger than that during recording by other means. You can do it like this. One of them is to make the number of revolutions of a rotary head the same during recording and reproducing, and to increase the number of heads used during reproducing compared to recording. For example, it is possible to provide two rotary heads spaced apart from each other by 180°, recording with only one of them and reproducing with both.
Another method is to use one rotary head that rotates at the same number of revolutions during recording and playback, and use this head to record data on, for example, every other track during recording, so that the playback locus is There are ways to avoid leaving books behind.

In addition, in the above-mentioned embodiment, the head width during playback is
Although Wh is assumed to be equal to the track width Wt of the recording track, the relationship (Wh>Wt) may also be established. For example, when (Wh = 1.5Wt), Fig. 6A
Reproduction signals S ₁ to _{S 4} as shown in FIG.
Corresponding playback data DT ₁ to _{DT 4} as shown in Figure B
are obtained sequentially. Furthermore, when (Wh=2Wt), reproduced signals S ₁ to _{S 4} as shown in FIG. 7 are sequentially obtained.

As is clear from these figures 6 and 7, by setting (Wh>Wt), the reproduced signal S/N
can be made better. On the other hand, since crosstalk occurs because two or more recording tracks are scanned simultaneously, it is necessary to take countermeasures against crosstalk.

As can be understood from the above explanation, according to this example, there is no need for tracking in which the head scans one-to-one with the recording track, so there is no need to perform high-precision tracking servo, and the mechanical Freed from precision. In other words, firstly, it is not necessary to specify the phase relationship between the recording track and the reproduction scanning trajectory, so a high-precision phase servo is not required.Secondly, the inclination of the recording track and the reproduction scanning trajectory Thirdly, since the recording track or playback scanning trajectory can meander, the precision of the tape path may be low.Fourthly, the tape path does not need to be accurate because the When winding the magnetic tape around the guide drum, there is no need to apply lateral pressure to the magnetic tape to regulate the position of the tape edge on one side, so the sliding contact between the rotating head and the magnetic tape can be made stable. .
For these reasons, it is also possible to form the tape guide drum from molded plastic, making it possible to manufacture the rotary head type playback device easily and inexpensively.

Note that, of course, the present invention can be applied to the case of reproducing digital information signals such as digital video signals and measurement data in addition to digital audio signals.

〔Effect of the invention〕

According to the present invention, there is an advantage that digital signals recorded at high density can be reproduced without performing high-precision tracking.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a recording system and a reproducing system according to an embodiment of the present invention, and FIGS. 2 and 3 are schematic diagrams showing the mechanical configuration and recording pattern of an embodiment of the present invention. FIG. 4 is a schematic diagram showing the structure of recorded data, FIG. 5 is a schematic diagram and time chart used to explain the operation of an embodiment of the present invention, and FIGS. 6 and 7
The figures are time charts used to explain other embodiments of the present invention. 1a and 1b are tape guide drums, 2 is a rotary head, 3 is a magnetic tape, 18 is TBC, T _{o -1} , T _o ,
T _o+1 is a recording track, and N ₁ to _{N 5} are playback scanning trajectories.

Claims (1)

[Claims] 1. A block is formed for each digital information signal of a predetermined length, a block address signal is added to each block, and each recording track is scanned twice on a tape on which a predetermined number of blocks are recorded. A rotary head that rotates at twice the number of revolutions during recording, and a memory in which the digital information signal reproduced by the rotary head is written in accordance with the block address signal, and the digital information written in the memory is provided. 1. A rotary head type reproducing device characterized in that the signals are read out in the order in which they were recorded so that the same chronological sequence as in the recording is obtained.