JPS60173749A - Automatic discriminating device of tape recording speed - Google Patents

Abstract

PURPOSE:To discriminate a recording speed by detecting an envelope of the reproduced output of a rotary magnetic head in the state where a magnetic tape is run at a prescribed speed at a reproducing start time and shaping the waveform of the detection output and measuring the period of one level of the shaped output with a timer. CONSTITUTION:When a reproducing key is operated, a control circuit 28 generates a reset pulse P1 to reset a flip-flop 29. A Q' output of the flip-flop 29 goes to the high level, and the control circuit 28 controls a motor driving amplifier 26 so that the tape running speed coincides with the LP mode. When data is recorded on a magnetic tape 1 in the LP mode, a counter 34 does not count FG pulses P3 at all. When data is recorded on the magnetic tape 1 in the SP mode, the counter 34 counts FG pulses P3 while pulses are in the low level. The envelope of the reproduced output of a pilot signal is detected, and the period of the low level is measured by the counter 34 to discriminate the recording speed.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a tape recording system for automatically determining the recording speed of a magnetic tape, for example, in a helical scan video tape recorder (hereinafter referred to as VTR). This invention relates to an automatic speed determination device.

[Technical background of the invention]

For example, in a beta format VTR,
It is now possible to record video signals on magnetic tape at different recording speeds.

In such a VTR, the speed at which the magnetic tape was recorded is determined at the time of playback, and -! - It is necessary to switch the H correction circuit, switch the audio system equalizer amplifier, switch the servo system loop gain, etc.

For the switching, generally a control pulse recorded on a control track is used. That is, the regenerated control pulse is transferred to the FG of the capstan.
The recording speed is determined by counting how many FG pulses are present per cycle of the (frequency generator) pulse and control pulse.

[Problems with background technology]

However, with the above configuration, if the control pulse is missing over a wide range for some reason, the recording speed cannot be determined.Furthermore, in the so-called 4-frequency pilot system VTR, which has undergone significant research and development in recent years, the control pulse is not applied to the magnetic tape. pulse? It is assumed that it will not be recorded. Therefore, in such a VTR, there is a problem that the recording speed cannot be determined at all using the above-described determination method.

[Purpose of the invention]

The present invention has been made in order to cope with the above-mentioned circumstances, and an object of the present invention is to provide an automatic tape recording speed determination device that can determine the tape recording speed without using control pulses.

[Summary of the invention]

This invention first uses a magnetic tape when starting playback.

is driven at a predetermined speed, and in this state, the envelope of the reproduction output of the rotating magnetic head is detected, the detected output is waveform-shaped into a pulse, and the period of one level of the shaped output is measured using a timer. By measuring the speed, the recording speed can be determined.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In the following description, a case where the present invention is applied to a four-frequency pilot system VTR will be described as a representative example.

As mentioned above, this four-frequency pilot type VTR does not record control pulses on the magnetic tape, and the tracking control of the rotating magnetic head is performed by pilot No. 1g recorded on the video track.

Here, first, we will discuss 1. Control of the tracking phase in MTR using the 4-frequency pilot system. This will be explained using an example.

FIG. 1 shows an example of a tape recording pattern of a four-frequency pilot type VTR.

In this case there is no traditional control track.

Tape 1 has video tracks 2, 3, 4, 5°6.7.
... are formed in order. Truck 2.4.6u
One of the two rotating magnetic heads (referred to as head A)
Tracks 3 and 5.7 were recorded using the other head (head B). A pilot signal is recorded on these tracks in a superimposed manner with a video signal, and these pilot signals are recorded on the video track in a predetermined order as pilot signals of four different frequencies. That is, tracks 2 to 7 all have false frequencies fx -ft -fs, f+
-fl, fz (hereinafter referred to as f).

, f4, . . . ) pilot signals are recorded superimposed on the video signal. Note that arrow A indicates the tape running direction, and arrow opening indicates the scanning direction of the rotating magnetic head.

During reproduction, the rotating magnetic head B scans, for example, track 5 as shown in the figure. At this time, this head B is on track 5.
The pilot signal P(f4) to the frequency recorded in n
(and video <g) and at the same time, from tracks 4 and 6 on both sides respectively
No. PCf*) - PCJ'l) is played (
Since the frequency of the pilot signal is low and the influence of azimuth loss is small, the pilot signals of adjacent tracks are also reproduced at the same time).

Based on the reproduced output of the pilot signal, the head (Al, (B
) will be described with reference to FIG. 2.

The signals reproduced from the rotating magnetic head &sB are input to reproduction preamplifiers 12m and 12b via rotary transformers 11a and 11bk, respectively, and are opened and closed by a head switching pulse PK input from a terminal 10. The signal is input to the switch SW. The outputs of the amplifiers 128 and 12b are taken out alternately from the switch SW, and this output is sent to the amplifier '13 for AGC (automatic gain control).
is input, and its amplitude is adjusted.

The output signal of this amplifier 13 is equalized by an equalizer amplifier J4'i.
i'' to a low-pass filter (LYE) 15, and the pilot signal is extracted.

This pilot signal output is supplied to the AGC detection circuit NOR. Furthermore, this pilot signal output is a converted pilot signal having the same frequency and order as the pilot signal supplied to heads A and H during recording.
1, the signal is input to a manually operated balanced modulator (BM) J6i and subjected to balanced modulation. At this time, as shown in the table, if the frequencies of the pilot signals P (fl) to P Cf4) are determined (the converted pilot signal naturally has a frequency equal to each of these pilot signal frequencies), then this Signals with frequency components of 3fH and fH are distributed from 8M16.

For example, when the head B is scanning the track 5 as shown in FIG. 1, as mentioned above, the pilot signal P(j'4)t of the frequency f4 is replayed from the track 5, and the adjacent tracks 4° on both sides 6 to reproduce pilot signals P Cfs ) -P (J't ) of frequency fs=fx, respectively. At this time, as a converted pilot signal, a converted pilot signal having the same frequency as the pilot signal P (, j'4) is supplied from the terminal 161 at 8M16VC (the servo is in the same state as before).

Therefore, the above frequency components are synthesized from 8M16,
In this case, the frequency component lf+- corresponding to the advance of the tape
Frequency component If corresponding to the ftl signal and tape delay
a-fsl signals are obtained. Note that the frequency component corresponding to the footing of track 5 is zero (Cf+ f+=o)
.

The level of the signal having frequency components of 3fH and fH from 8M16 is proportional to how far the head A or [BO scan is shifted to the left or right. In other words, depending on whether the scanning of heads A and B is delayed or ahead, the level of one of the signals having frequency components of 3fH and fH will be higher than the other. Delayed at B (
The frequency component corresponding to the head switching pulse P5 is inverted, as will be explained later.
It is sufficient to switch switch sw, 1 from K.1 Table (however, fH is the horizontal synchronization frequency) The output of 8M16 is a band pass filter (BPF) is, i to extract the frequency components of glaze and 3fH, respectively.
input to s. f extracted in BPFIB and 19
It has frequency components of H and 31H, and their levels are detected by the fc multiplied signal level detectors 20 and 21, and the switch sw
2 is input. This switch sw is as described above.

Head person and B's advance, slow 7'1. Since the frequency components corresponding to 1 and 2 are reversed, it can be used for switching. In other words, when playing with Head B, the frequency component corresponding to the advance is 111 ((the delay is the same 3 fH), and when playing with Head B, the frequency component corresponding to the advance is 3 fHC.
Since the delay is fH], this switch sw2 is set such that when the head is playing, BPFJ 9 for afH is output to the voltage comparator 22 terminal, and BPFM 8 for fH is output to the voltage comparator 22 terminal. It can be switched so that one terminal can be operated manually.
When head B is performing playback 1, the situation is exactly reversed. The levels of the frequency component signals of the voltage comparator 22, 1fH, and 23fH are compared, and the difference is output.

This phase difference output is passed through the loop filter 23 to the adder 2.
4. Then, the adder 24 discriminates the capstan motor MO rotation frequency and adds it to the output signal of the AFC (automatic frequency control) discriminator 25 for setting it to a predetermined value, and the output signal is added to the output signal of the AFC (automatic frequency control) discriminator 25 to set the capstan motor MO rotation frequency to a predetermined value. The signal is supplied to the motor M as a motor control signal. Due to the above,
Since APC (automatic phase control) of the capstan motor M that drives the tape is applied so that the phase difference output becomes the reference level, tracking control is performed so that Heraton and B accurately scan their own video tracks. That is, tape feeding is controlled so that two signal levels having frequency components of fH and 3fH always have the same or constant voltage difference.

Next, what is the configuration and operation for determining tape recording speed, which is a feature of this invention? explain.

In a four-frequency pilot type VTR, two types of tape recording speeds are currently being considered: a short time mode (hereinafter referred to as -8P mode) and a long time mode (hereinafter referred to as LP mode). SP mode has already been standardized, but LP mode has not yet been standardized.This LP mode is % 1/2 speed of SP mode.

Although direct settings such as 1/3 speed and 1/4 speed are possible, 1/2 speed is currently considered promising.

Therefore, in the following explanation, %SP is used as the tape recording speed.
Consider two types: SP mode and P mode.

The case where the LP mode is the sound speed of the SP mode will be described as a representative example.

In this invention, at the start of playback, either the magnetic tape 1tl-8P mode or the LP mode is run in the LP mode, and during this time the envelope of the playback output of the pilot signal is detected, and the level change of the detected output is monitored. By doing so, it is determined whether the tape recording speed is in SP mode or LP mode.

To explain this using FIG. 2, in the figure, 27 is a keyboard that has various operation keys such as record and playback keys, and 28 is a keyboard that uses keys manually from the keyboard 27.
This is a control circuit that outputs control signals that control various operations of the TR.

Now, assuming that the playback key is operated at time t as shown in FIG. 3(a), the control circuit 28 generates reset pulses p, c
(see FIG. 3(b)) t-occurs, flip-flop 29
Reset. Due to this.

The Q output of the flip 7a knob 29 is at the Nohei level (hereinafter referred to as
In response to this, the control circuit 28 controls the motor drive amplifier 26 so that the tape running speed matches the LP mode. The rotational speed of the motor M gradually increases as shown in FIG.
After T.

The tape running speed reaches a speed that matches the LP mode.

The output of the LPFZ 5 is further supplied to an envelope detection circuit 30, where the envelope of the reproduced output of the pilot No. 1g is detected. This detection output is supplied to an inverter circuit 33 through a waveform shaping circuit 31 capable of converting an AC signal into a pulse waveform.The inverter circuit 33 inverts the shaped output of the waveform shaping circuit 31 and stores the initial data (set) in a down counter 34. data) is given as a load pulse pt.

Now, as mentioned above, since the playback speed is set to LP mode, if magnetic tape 1 is recorded in LP mode, it will be played back at 1x speed, and the envelope detection output will be as shown in Figure 4 (a). As shown, the result is a flat DC signal.

On the other hand, if the magnetic tape was recorded in the SP mode, the playback mode will be double speed playback. In this case, the scanning trajectories of heads A and B span three video tracks, as shown by flashes in FIG. rL
Oh, in the diagram.

A typical case is shown in which head B scans across tracks 4, 5, and 6. In this case, head B scans across three tracks as described above. Because of scanning, three pilot signals P(fs)=P (74) - P Cjs ) can be obtained without considering crosstalk from adjacent tracks. However, since VTRs generally use azimuth recording, even if the pilot signal is set to a low frequency range where it is difficult to completely eliminate the influence of the azimuth loss effect, as mentioned above, the main track Compared to the pilot signal p (74) from track) 5, the levels of pilot signals P Cf s) and P(fl) from tracks 4 and 6 formed by other heads A are so small that they can be ignored. Therefore, as the envelope detection output of the pilot signal, it is safe to consider only the detection output of the pilot signal from the main track +f, and this also applies when head A is scanning.

The total reproduced output of the pilot signal in this case is shown in Figure 4(b), and the detected output is shown in Figure 4(c).This repetition period is for one field (IF).Waveform shaping circuit 31 converts this detected output into pulses as shown in FIG. 4(d).

From the above, when the magnetic tape 1 is recorded in the LP mode, the output terminal of the waveform shaping circuit 31 receives a DC 1B signal, that is, an H level signal as shown in Fig. 84(a). When n'fc is recorded in the SP mode, a pulse as shown in FIG. 4(d) is obtained. These signals are inverted by an inverter circuit 33, and then sent to a counter 3.
It is supplied to the load terminal LO of No. 4.

A down counter 34 counts the FG pulse Psk given to the AFC valve gain divider.

Set 1, counting down from the 1st shift of a certain set.
Directly, it is binary and 4 bits ABCD”=”1llll”
The value of is given. in this case.

The counter 34 receives a load input (FIG. 4(a) or (d)
) is a low level (hereinafter referred to as L
During the period (denoted as level), continue to load set 1 shift,
JIJ [does not perform 121 operation, but the load input is H level, stops loading the set value,
Executes all counting operations.

Therefore, when the magnetic tape 1 is recorded in LP mode, the counter 34 is completely %FG Balloon
P, is not counted, whereas magnetic tape 1 is S.
If it was recorded in P mode, please refer to Figure 4 (dl
During the period when the pulse shown in is at L level, the FG pulse Pst- is counted as shown in FIG. 4(f). counter 34
The set value is set to such a value that the counter 34 counts down to 'oooo' during period 1 when the load input is at H level. Therefore, if the magnetic tape is recorded in SP mode, , while the load input is at H level, a borrow signal sB is always obtained from the counter 34 as shown in FIG. 4(g), and the flip-flop 29 is set. The output becomes L level, and in response to this, the control circuit 28 controls the motor drive amplifier 26 to drive the magnetic tape 1 in the SP mode. Therefore, even if the magnetic tape 1 is recorded in SP mode, it can be automatically reproduced in SP mode. If the magnetic tape 1 is recorded in LP mode, the counter 34 will not output the borrow signal SB.

It plays in LP mode without any problems.

The control circuit 28 applies a reset pulse P, (see FIG. 3(e)) to the counter 34 at the start of playback, and during the unstable period until the tape running speed reaches the LP mode, the counter 34 performs a counting operation. to prevent malfunctions.

As described in detail above, in this embodiment, the recording speed is determined by detecting the envelope of the reproduced output of the pilot signal and measuring the period of the L level with the counter 34. Even without the control pulse, the recording speed is The discrimination becomes 0T ability. In this case, by appropriately setting the set value of the counter 34, it is possible to minimize malfunctions due to changes in the envelope due to instantaneous loss of pilot signals due to some cause.

In the explanation above, the case where the envelope of the reproduced output of the pilot signal is detected is explained, but it goes without saying that the envelope of the video signal may also be detected.

In addition, in the above explanation, the case where the LP mode is the connecting speed of the SP mode has been explained, but - 2 speeds with film formation...
・It is also applicable when . Even in such a case, the recording speed can be determined because the detection output of the envelope fluctuates when reproduction is performed at a speed different from the recording speed. Note that the fluctuation frequency of the detection output is in the LP mode; however, 'EsW: the frequency of the head switching pulse.

Further, in the above description, the case where the magnetic tape is first driven to run in the LP mode at the start of reproduction has been described, but it is of course possible to start from the 8F mode.

Furthermore, the running drive may be started at a speed different from either the LP mode or the SP mode. In this case, the detection output of the envelope will vary no matter which mode the magnetic tape 1 is recorded in. However, since the fluctuation frequencies (A) are different, it is possible to determine the recording speed.

Further, the counting operation may not be performed in four lines during the L level period, but may be performed during the H level period.

In addition, to measure the period of one level of the envelope detection output, a digital counter can be used to measure the period of one level of the envelope detection output. It may be better to process it separately.

〔Effect of the invention〕

Furthermore, according to the present invention, it is possible to provide an automatic tape recording speed discrimination device that can discriminate based on tape recording speed without using control pulses.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a tape recording pattern in the 4-frequency pilot system, Fig. 2 is a circuit diagram showing an embodiment of the tape recording speed automatic discrimination device according to the present invention, and Fig. 3 is the operation of one embodiment. 4th time chart to explain
The figure is a signal waveform diagram of each part for explaining the entire operation of one embodiment, and FIG. 5 is a diagram showing a head scanning pattern for explaining the entire operation of one embodiment. 26... Motor drive amplifier, 1M... Capstan motor % 27... Keyboard, 28... Control circuit, 29... Flip-flop, 30... Envelope detection circuit, 31... Waveform Shaping circuit, 33... Inverter, 34... Down counter. Applicant's agent Patent attorney Takehiko Suzue No. 1-7 No. 3-j (e) P4-f-]-1111

Claims (1)

[Claims] A helical scan type magnetic recording and reproducing device that records signals on a magnetic tape using a rotating magnetic head so as to form oblique tracks. and a tape running means for driving the entire magnetic tape to run at a predetermined speed during reproduction. an envelope detection means for detecting an envelope of a signal reproduced by the rotating magnetic head from a magnetic tape being driven to run by the tape running means; Waveform shaping means for shaping the entire waveform of the detected output from the envelope detection means to obtain pannonce. An automatic tape recording speed discrimination device is provided with a timer means for measuring the period of one level of the waveform shaping output from the waveform shaping means and a timer means for discriminating the recording speed of the magnetic tape.