JPH0679399B2 - ATF circuit of rotary head type digital audio pre-coder - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an ATF (Automatic Tarck) of a rotary head type digital audio tape recorder generally called R-DAT.
Finding) circuit.

[Technical background of the invention]

The R-DAT converts an audio signal into a PCM, and records this on a diagonal one track on a magnetic tape as a recording medium by a helical scan type rotary head every unit time, and records the recorded digital signal. It is for playing.

The format of the track actually recorded on the magnetic tape by the R-DAT has a pattern as shown in FIG. In the figure, for each of MARGIN, PLL, POSTAMBLE,
A frequency signal of frequency 1 / 2f _M (f _M = 9.4 MHz) and a frequency signal of frequency 1 / 6f _M are recorded in the IBG. SUB
And PCM consist of blocks as shown in Fig. 3 (b),
The SYNC of each block has a 10-bit (fixed 9-bit) structure, and the rest have various patterns depending on the location and audio signal. SUB has 8 blocks and PCM has 128 blocks. The numerical values in FIG. 3A indicate the number of blocks occupied by each area.

The areas of ATF-1 and ATF-2, which are arranged between SUB-1 and PCM and between PCM and SUB-2, enable the rotary head to scan the recording track correctly during reproduction. This is for enabling tracking control to be performed by the output of the rotary head without providing a special head.

That is, the ATF area is recorded at the beginning and end of each track when the PCM signal is time-axis compressed and the tracks are diagonally formed on the magnetic tape without a guard band by the two rotary heads and recorded. Tracking pilot signals are recorded separately from the PCM signal in a recording area, and during reproduction, the recording track is scanned by a rotary head whose scanning width is wider than the width of the track. It is used to control the tracking of the rotary head by the reproduction output of the pilot signal from.

The track pattern for this ATF is defined as shown in FIG. 4, and the pattern shown is the drum diameter.
A case of 30 mm, a drum winding angle of 90 ° and a rotation speed of 2000 rpm will be described.

ATF-1 and ATF in the front and back of each track
-2 has a low-frequency signal f ₁ with a small azimuth effect as a pilot signal for tracking, which detects the level of crosstalk from both adjacent tracks during reproduction and detects the crosstalk component of both adjacent tracks. It is used to obtain the level difference as a tracking error signal.
A low frequency signal of f _M / 72 (130 KHz) is used as the pilot signal f ₁ .

Further, in ATF-1 and ATF-2, a sync signal for discriminating the position where the pilot signal f ₁ is recorded is recorded. If there is crosstalk in the sync signal, it is impossible to distinguish between the on-track and the adjacent track. Therefore, a frequency that has an azimuth effect and a pattern that does not exist in the PCM signal is selected. When the head corresponding to + azimuth is A and the head corresponding to −azimuth is B, the sync signals are different from each other in order to distinguish the A head and the B head, and the frequency is different for the A head. f _M / 18
A sync 1 signal f ₂ of (= 522 KHz) and a sync 2 signal f _{3 of} frequency f _M / 12 (= 784 KHz) are recorded at predetermined positions for the B head.

In the R-DAT, the erasing head is not provided, and the rewriting of the signal is performed by so-called overwriting in which overwriting is performed on the previous recording. Therefore, the erase signal f ₄ having the frequency f _{M /} 6 (= 1.56 MHz) is recorded at a predetermined position for erasing the pilot signal f ₁ , sync 1 signal f _2, and sync 2 signal f ₃ of the previous recording. It

The positions of the ATF pilot signal are different on the on-track and on both adjacent tracks, and the level of the on-track pilot signal and the level of the pilot signal on both adjacent tracks are temporally different, and three types of levels are sampled respectively. Are arranged so that they can.

Five blocks are allocated to each ATF area of ATF-1 and ATF-2, and pilot signals are allocated to two blocks of them.
f ₁ is recorded. The sync signals f ₂ and f ₃ are one block from the center of the position where one adjacent track is recorded or
It is recorded using 0.5 blocks. The pilot signal f ₁ of the other adjacent track is recorded such that the center thereof is located two blocks after the beginning of the sync signal recorded on the on-track. The sync signal of one block is assigned to the odd frame and the sync signal of 0.5 block is assigned to the even frame.

As described above, in the ATF, the sync signal frequency differs depending on the A head and the B head, and the sync signal recording length differs between the odd frame and the even frame. Therefore, all four consecutive tracks have different ATF,
It can be distinguished. The above ATF pattern is a complete type in which 4 tracks are repeated every 4 tracks.

By the way, when the magnetic tape recorded in the format as shown in FIG. 3A is reproduced by the rotary head, the RF signal as shown in FIG. 5A is obtained from the rotary head.
When this RF signal is obtained, for example, by reproducing the odd-numbered frame track (A) in FIG. 4, a pilot signal f ₁ as shown in (b) is obtained by passing it through a bandpass filter (BPF) of 130 KHz. Is obtained.

The section I is based on the on-track pilot signal, and the sections II and III are (B) odd frame track and (B)
This is due to the crosstalk of the pilot signals of the even frame tracks. When the rotary head is scanning correctly on the on-track, the envelope levels of sections II and III, that is, VII and VIII in (c) should be the same, but if there is a track deviation, VII ≠ VIII, and The amount and direction of displacement of the rotary head with respect to the on-track can be known from the size and polarity. Therefore, it becomes possible to drive the rotary head on the on-track by finely adjusting the tape speed by operating the capstan servo by the difference between VII and VIII.

Conventionally, ATF for performing tracking control as described above
A circuit as shown in FIG. 6 has been generally used.

In the figure, 1 is a sync equalizer amplifier that emphasizes and amplifies a sync signal frequency component in an RF signal obtained by reproduction by a rotary head, 2 is a sync detection circuit that detects a sync signal from the output signal of the sync equalizer amplifier 1, 3 Is a sample pulse generation circuit that generates sample pulses SP1 and SP2 according to the sync signal detected by the sync detection circuit 2.

Reference numeral 4 is a pilot detection circuit for detecting a pilot signal frequency component in the RF signal, and 5 is a rectification circuit for rectifying the detection output signal of the pilot detection circuit 4 and outputting a DC voltage signal having a magnitude corresponding to the pilot signal level.

Reference numeral 6 denotes a first sampling hold (S / S) for sampling and holding the level of the voltage signal from the rectifier circuit 5 with the sample pulse SP1 from the sample pulse generating circuit 3.
H) circuit, 7 is the level of the voltage signal from the rectifier circuit 5 and S / H
A differential circuit that takes the difference from the level held in the circuit 5, and 8 is the sample pulse from the ampoule pulse generation circuit 3 for the level of the level difference signal obtained at the output of the differential circuit 7.
This is the second S / H circuit that samples and holds by SP2.

The generation of the sample pulse SP1 by the sample pulse generation circuit 3 is performed in response to the detection of the sync signal, and the generation of the sample pulse SP2 is performed two blocks after the generation of the sample pulse SP1. Therefore, the voltage signal level held in the S / H circuit 6 corresponds to the level of the crosstalk component of the pilot signal of one adjacent track, and the S / H
The level difference signal level held in the circuit 8 corresponds to the level difference of the crosstalk components of the pilot signals of both adjacent tracks. The level difference held in the S / H circuit 8 has a magnitude and polarity according to the amount of displacement of the rotary head from on-track and its direction. Therefore, by returning this as a control signal for the capstan servo 9, Tracking is possible.

The tracking as described above is performed at four points during one rotation of the rotary drum having the two rotary heads A and B.
That is, the rotary heads A and B are alternately operated by switching with a head switching pulse (HSWP) signal as shown in FIG. 7 (a) to reproduce the A channel track and the B channel track on the magnetic tape, respectively. Then, an RF signal as shown in FIG. 7 (b) is obtained. In the RF signal obtained by reproduction by each rotary head,
ATF-1 and ATF-2 are included, and tracking is performed in each ATF.

[Problems to be solved by the invention]

In the case of R-DAT, tracking is performed using the above-mentioned ATF circuit not only in the normal reproduction mode but also in the after-recording mode, but there is a problem that the tracking becomes unstable in the after-recording mode.

That is, at the time of after-recording, an extra high-frequency writing can be performed by setting up after-recording pulses of about two blocks wide before and after the data to be written so that the previous signal remains unerased even when the recording position shift occurs. Done.

If the timing of the after-recording timing pulse (AFRETP) is shifted, its width is increased, or its trailing edge is blunted, the after-recording recording voltage signal is ATF.
Will be superposed on the pilot signal. Therefore, it becomes impossible to sample and hold the level according to the correct track deviation amount in the S / H circuit 8, and the tracking becomes unstable.

For example, at the time of post-recording of the SUB code, in the case of ATF-1 of the A channel track, as shown in FIG.
In case of ATF-2, 5 blocks by 1 generation timing,
As shown in FIG. 8B, there is a margin of 6 blocks from the generation timing of the sample pulse SP2 to the rising edge of the post-recording timing pulse. On the other hand, the margins for ATF-1 and ATF-2 of the B channel track are 2 blocks and 3 blocks as shown in FIGS. 9 (a) and 9 (b), respectively.

Also, at the time of PCM dubbing, ATF of A channel track
The margins of -1 and ATF-2 are 3 blocks and 1 block respectively as shown in FIG. 10, and the margins of ATF-1 and ATF-2 of the B channel track are 6 blocks and 1 block respectively as shown in FIG. There are 3 blocks.

As is apparent from the above, the tracking instability phenomenon during post-recording is particularly likely to occur in the ATF-1 of the B channel track during the SUB after-recording and in the ATF-2 of the A channel track during the PCM after-recording.

[Object of the Invention]

The present invention has been made in order to eliminate the above-mentioned drawbacks of the prior art, and provides an ATF circuit of a rotary head type digital audio tape recorder which prevents unstable tracking during SUB code dubbing or PCM. It is an object.

[Outline of Invention]

In the SUB code after-recording mode, the tracking operation by the signal in the ATF-1 area of the B channel track among the signals in the four AF areas reproduced by the two rotating heads is prohibited. The unstable tracking operation is eliminated by prohibiting the tracking operation by the signals in the ATF-2 area of the A channel track among the signals in the four ATF areas reproduced by.

〔Example〕

An embodiment of the ATF circuit according to the present invention will be described below with reference to the drawings. However, the same parts as those of the conventional one described with reference to FIG. 6 are designated by the same reference numerals, and detailed description thereof will be omitted. ing.

FIG. 1 is a circuit block diagram showing an embodiment of an ATF circuit according to the present invention. In the figure, head switching pulse (HSW
As shown in FIG. 2 (b), P) shows the A channel track at the L level by one of the two rotary heads,
The B channel track is reproduced by the other at the level so that the RF signals of the A channel track and the B channel track as shown in FIG. 2 (a) can be obtained. The RF signal length of each track is 7.5 ms.

The RF window pulse (RFW) is at the L level for a certain period of time as shown in FIG. 2 (c). SUB post-recording signal (SUBAFRE) and PCM
The dubbing signal (PCMAFRE) is always kept at H level in dubbing mode.

The RF window pulse is a mono-multivibrator (MM) that is triggered when the input falls from H to L level and generates a pulse that goes to H level for 3.8ms at the output.
Applied to 10 inputs. The output of the mono multivibrator 10 is connected to the other inputs of the NAND gate 11 and the OR gate 12, respectively, to which the head switching pulse is applied to one input.

The output of the NAND gate 11 is input to the other input of the AND gate 13 where the SUB after-recording signal is input to one input, and the output of the OR gate 12 is input to the other input of the AND gate 14 where the PCM after-recording signal is input to one input. It is connected.

The SUB dubbing signal and the PCM dubbing signal are also applied to the input of the OR gate 15. The output of the OR gate 15 is connected via the inverter 16 to one input of the OR gate 17. The other input of OR gate 17 is AND gate 13 and
14 outputs are connected. The output of the OR gate 17 is connected to the other input of each of the AND gates 18 and 19 to which the sample pulses SP1 and SP2 are applied, respectively.

With the above configuration, in the normal reproduction mode, the SUB after-recording signal and the PCM after-recording signal are both at the L level, so that the output of the OR gate 17 is always at the H level and the AND gates 18 and 19 are in the open state. . Therefore, the sample pulses SP1 and S from the sample pulse generating circuit 3 are
All of P2 are S / H via AND gates 18 and 19, respectively.
The signals are applied to the circuits 6 and 8, and tracking is performed by signals in all ATF regions.

In the SUB after-recording mode, the output of the NAND gate 11 becomes L level and the output of the OR gate 12 becomes H level in the first half of the B channel track.
Since the other input of the OR gate 17 is at the L level, all the inputs of the OR gate 17 are at the L level and its output is also at the L level. Therefore, the AND gates 18 and 19 are closed during this period, the sample pulses SP1 and SP2 are not applied to the S / H circuits 6 and 8, and the tracking of the B channel track at ATF-1 is not performed. The ATF-1 of this B channel track is 2 as described above with reference to FIG. 9 (a).
Since there is only a margin of blocks, the unstable tracking operation is eliminated by prohibiting the tracking operation.

In the PCM dubbing mode, the output of the AND gate 13 is always L level, and the output of the AND gate 14 is L level only in the latter half of the A channel track. Therefore, the AND gates 18 and 19 are closed in the latter half period of the A channel track, and the sample pulses SP1 and SP2 are S / S through the gate.
It is not applied to the H circuits 6 and 8. Therefore, ATF-2 tracking of the A channel track is not performed. As described above with reference to FIG. 10, the ATF-2 of the A channel track has a margin of one block and is likely to cause tracking disturbance. Therefore, by prohibiting this tracking operation, tracking is stabilized.

When both SUB dubbing and PCM dubbing are performed at the same time, the tracking operation in the ATF-2 of the A channel and the ATF-1 of the B channel track is prohibited to prevent the disturbance of the tracking.

In the illustrated embodiment, when SUB dubbing and PCM dubbing are performed at the same time, tracking in two ATFs is prohibited. However, if two or more ATFs are killed, a tracking error will increase, so either one should be used. It may be preferable to set it to.

Further, in the illustrated embodiment, the head switching signal, the RF window pulse and the output of the mono multivibrator are used to control the inhibition of the tracking operation, but the present invention is not limited to this, and during the after-recording operation, As long as at least one of the four places that disturbs tracking can be selected, the same effect as the above-described embodiment can be obtained.

[Effect]

As described above, according to the present invention, when the SUB code is recorded in the after-recording mode, it is reproduced by two rotary heads.
Among the signals in the ATF area at some locations, the tracking operation by the signal in the ATF-1 area of the B channel track, which has a small margin with the after-recording timing and is easily affected by the after-recording recording voltage, is prohibited. You can do SUB code dubbing with.

Also, in the PCM post-recording mode, among the signals in the four ATF areas reproduced by the two rotary heads, the signal in the ATF-2 area of the A channel track, which has a small margin with the post-recording timing and is easily affected by the post-recording voltage. Since the tracking operation by is prohibited, PCM dubbing can be performed under stable tracking.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a circuit according to the present invention, FIG. 2 is a timing chart showing the state of each part in FIG. 1, and FIG. 3 is a track format and block format of R-DAT. FIG. 4 is a diagram showing an ATF track pattern of R-DAT, FIG. 5 is a diagram for explaining the principle of tracking control by the track pattern of FIG. 4,
FIG. 6 is a circuit block diagram showing a conventional circuit example, FIG. 7 is a timing chart diagram showing a head switching signal and an RF signal, and FIGS. 8 and 9 are positional relationships between after-recording and ATF during SUB after-recording. And Fig. 10 and Fig. 11 show P
It is explanatory drawing which shows the positional relationship between after-recording at the time of CM after-recording, and ATF. 10 …… Mono multi-vibrator, 11 …… Nand gate,
12,17 …… OR gate, 13,14,18,19 …… AND gate,
16 ... Inverter.

Claims (2)

[Claims] 1. An ATF-1 area and an ATF which are respectively recorded on the tracks reproduced by the respective rotary heads by sequentially reproducing the A channel track and the B channel track on the magnetic tape by each of the two rotary heads. -In the ATF circuit of the rotary head type digital audio tape recorder which performs tracking by the signal of the -2 area, in the after-recording mode of the SUB code, among the signals of the four ATF areas reproduced by the two rotary heads, the B channel track An ATF circuit for a rotary head type digital audio tape recorder, characterized in that it has circuit means for prohibiting a tracking operation by a signal in the ATF-1 region. 2. An ATF-1 area and an ATF which are respectively recorded on the tracks reproduced by the respective rotary heads by sequentially reproducing the A channel track and the B channel track on the magnetic tape by each of the two rotary heads. In the ATF circuit of the rotary head type digital audio tape recorder which performs tracking by the signal of the -2 area, the ATF of the A channel track among the signals of the four ATF areas reproduced by the two rotary heads in the PCM dubbing mode. An ATF circuit for a rotary head type digital audio tape recorder, characterized in that it has circuit means for prohibiting tracking operation by signals in two areas.