JPH0566663B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a blank detection device for detecting a tape blank portion in a magnetic recording/reproducing device using a rotary head to detect a tape position where a new recording is to be made.

[Prior art and its problems] Magnetic recording and reproducing devices using rotating heads, e.g.
In a VTR (video tape recorder), when performing continuous shooting or cueing, accurate positional information for each field is often required. When performing continuous shooting or cueing as described above, conventional methods often used in radio cassettes, etc., record a position detection signal between pieces of information, or record a thread with a signal level of the read information. It is detected depending on whether it is higher or lower than the Tushijord level. However, in the above-mentioned conventional method, an integrating circuit with a large time constant must be provided in the detection circuit in order to eliminate the influence of dropouts and the like. Further, by providing the above-mentioned integrating circuit, there is a problem that the length of the tape from when information is missing to when the running system actually stops varies greatly due to variations in its time constant.

[Object of the Invention] The present invention has been made in view of the above points, and provides a method for reliably detecting the end or start position of recorded information on a magnetic tape during high-speed playback without recording a positioning signal even during high-speed running. The object of the present invention is to provide a blank detection device that can perform the following tasks.

[Summary of the Invention] The present invention takes advantage of the fact that the envelope signal is interrupted between tracks during high-speed playback, pulses it and counts it, and even when there is no position readout signal, the relative position/relative time to the recorded information can be determined. This allows accurate detection.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numerals 11a and 11b are first and second heads that read out video signals recorded on a videotape and input them to the reproduction amplifier 12.
This reproduction amplifier 12 is connected to the heads 11a and 11.
The playback signal from b is sent to the head switch pulse HSW.
The signals are alternately selected field by field, amplified to an appropriate level, and output to the color signal processing circuit (not shown) and the high-pass filter 13. This high-pass filter 13 is a filter that passes only the FM signal, and its output is sent to a luminance signal processing circuit (not shown) and an AGC circuit 14. This AGC circuit 14 holds the FM signal level from the high-pass filter 13 constant and inputs it to the dropout detection circuit 16 in the blank detection section 15. This dropout detection circuit 16 detects a state in which the FM signal level is below a threshold and outputs a signal.The detection signal is sent to a dropout compensation circuit (not shown), and is also sent to a low pass filter 17 and a waveform shaping circuit. The signal is inputted to the first counter 19 via 18 as a count-up signal. Further, the head switch pulse HSW is inputted to the reset terminal of the first counter 19 via a frequency dividing circuit 21 and a pulse shaping circuit 22. The frequency dividing circuit 21 has a head switch pulse.
When the HSW is input, the frequency is divided into a signal with a period of about 3 seconds, for example, and output to the pulse shaping circuit 22. This pulse shaping circuit 22 shapes the waveform of the input signal, changes the duty ratio for a reset pulse, and sends the output signal to a pulse generating circuit 23 that generates a continuous pulse equivalent to a dropout detection pulse and a second counter 24 as a reset signal. Enter as . In addition, the first counter 19 and the second counter 24
A control signal instructing to start and stop counting is given from a counting start/stop control circuit 25. The first counter 19 and the second counter 24
The count radial numbers are set so that the most significant bit MSB is output at the same period and at a slightly shorter period than the period of the reset pulse RST outputted from the pulse shaping circuit 22. Then, the most significant bit of the first counter 19 and the second counter 24
The MSB output is an exclusive OR circuit (hereinafter referred to as EX
(abbreviated as an OR circuit) 26, and the output of the EX OR circuit 26 is sent to a CPU (not shown) as a blank detection signal.

Next, the operation of the above embodiment will be explained with reference to the timing chart of FIG. When a cue operation is performed on the videotape, a control command is sent from the CPU to the count start/stop control circuit 25, and the count start/stop control circuit 25 commands the first counter 19 and the second counter 24 to start counting. is given. As a result, the first counter 1
9 and the second counter 24 become operational. As shown in FIG. 2, the reproduction amplifier 12 receives a head switch pulse HSW whose signal level is switched between high and low for each field. The reproduction sample 12 alternately selects the video heads 11a and 11b for each field by the head switch pulse HSW, and amplifies the read signal to an appropriate level. The output signal of this reproduction amplifier 12 is then passed through a high pass filter 1.
3, only the FM signal is extracted and the AGC circuit 14
is maintained at a constant level. Therefore, when searching for the beginning of a tape, the forward search cue is performed at a speed that is, for example, 11 times the normal playback speed. In this way, when the forward search cue is 11 times the speed, the video heads 11a and 11b cross 11 tracks as shown in FIG. (The shaded area in Figure 3)
Only the image signal is output. Therefore, AGC circuit 1
4, five diamond-shaped waveform signals A are output corresponding to tracks with matching azimuths, as shown in FIG. 2, and the envelope signal is interrupted between the tracks. As a result, when the speed is 11x as mentioned above, noise bars appear, one at the top and bottom of the screen, and four noise bars at the center of the screen. However, the above AGC
The output signal of the circuit 14 is input to a dropout detection circuit 16 within the blank detection section 15. This dropout detection circuit 16 is connected to the AGC circuit 14.
When the signal level of the output signal A becomes below the threshold level, this state is detected and a signal is output. The dropout detection signal output from the dropout detection circuit 16 is
The low-pass filter 17 removes noise and small-scale dropout detection signal components, and then the waveform shaping circuit 18 shapes the waveform, and the output signal C of the waveform shaping circuit 18 is sent to the first counter 19 as a count-up signal. On the other hand,
The head switch pulse HSW is frequency-divided by a frequency dividing circuit 21 in the blank detecting section 15 into a signal having a cycle of about 3 seconds, further waveform-shaped by a pulse shaping circuit 22, and outputted as a reset pulse RST. Therefore, while the tape is being fast-forwarded by the forward search cue, the first counter 19 and the second counter 24 are reset at regular intervals by the reset pulse RST. and,
The first counter 19 counts the dropout detection signal C from the waveform shaping circuit 18, and the second counter 24 counts the output pulses D from the pulse generation circuit 23. In this case, pulse generation circuit 2
Since the output signal D of No. 3 is a continuous pulse equivalent to the dropout detection signal, the video head 11
While the recording signal is being read from the video tape by the signals a and 11b, the first counter 19 and the second counter 24 perform exactly the same counting operation, as shown in FIG. The count contents are the same.

When the video tape is run to an area where no video signal is recorded and the output of the AGC circuit 14 becomes "0", the dropout detection circuit 16, the low-pass filter 17, the waveform shaping circuit 18
The output signal of becomes a constant level, and the first counter 1
The counting operation of 9 stops. However, the second counter 24 receives the output pulse D of the pulse generation circuit 23.
, so the counting operation continues as it is. At this point, the output signals E and F of the first counter 19 and the second counter 24 are both “0”.
, and the output of the EX OR circuit 26 is held at "0". After that, the second counter 24
The bits count up sequentially, and the most significant bit is reached after a little less than 3 seconds have elapsed since the start of the counting operation.
When the MSB becomes "1", that is, when the output E of the first counter 19 is "0", the second counter 24
When the output F becomes "1", the EX OR circuit 26 outputs a "1" signal. Then, the output signal G of this EX OR circuit 26 is sent to the CPU as a blank detection signal of the blank detection section 15. CPU
When the blank detection signal is sent from the EX OR circuit 26, the videotape stops running, and if necessary, the videotape is rotated in the opposite direction.
Fast-forward for ~3 seconds, return to the recording end, and stop. The beginning of the videotape is located as described above.

In the above embodiment, the first counter 19 and the second counter 24 are provided, and both the counters 19 and 24
Although the blank detection signal is obtained by comparing the outputs of the two, the blank detection signal may be obtained in other ways as shown in FIGS. 4a and 4b. That is, in FIG. 4a, the dropout detection signal is counted by the sampling counter 31, and the count output is inputted to the count terminal of the counter 32. The sampling counter 31 is set to 1.5 msec for each track, for example.
The input signal is sampled and counted 16 times within the period, and NO is selected if the number of low level signals is more than a certain number.
A blank signal NBL (L) is output, and when the number is less than a certain value, a blank signal BL (H) is output. The counter 32 performs a count-up operation based on the blank signal BL output from the sampling counter 31. Further, this counter 32 is reset by the output of the counter 33. This counter 33
is a counter for determining the search period, which counts clock pulses ck and provides a reset signal to the counter 32 at regular intervals. Therefore, the counter 32
If the counter 32 overflows before being reset by the counter 33, a blank detection signal is output from the counter 32 and sent to the CPU.

4b, the counter 33 is omitted in the circuit of FIG. 4a, and the counter 32 is
is counted up, and the counter 32 is reset by the NO blank signal NBL. That is, in FIG. 4b, when the sampling counter 31 outputs a predetermined number of consecutive blank signals BL, the counter 32 outputs a blank detection signal and sends it to the CPU. If the NO blank signal NBL is output even once while the blank signal BL is being output from the counter 31, the counter 32 is reset and no blank detection signal is output.

In each of the above embodiments, a forward search at 11 times speed has been described, but the present invention can also be applied to a backward search, and the search speed is not limited.

[Effects of the Invention] As detailed above, according to the present invention, the discontinuation of the envelope signal between tracks is used to pulse it and count it, thereby detecting the relative position/time relative to recorded information. Therefore, there is no need to record a position readout signal, and even if the videotape is being fed at high speed, the end or start position of the recorded information can be accurately detected. Furthermore, since the position information is detected digitally, the detection operation can be performed very stably, and the same operation can be performed even if the equipment or tape is different. It is not affected by the winding position.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; Fig. 1 is a block diagram showing the circuit configuration, Fig. 2 is a timing chart for explaining the operation, and Fig. 3 is a track diagram for forward search at 11x speed. FIGS. 4a and 4b are block diagrams showing other embodiments of blank detection. 11a, 11b...video head, 12...playback amplifier, 13...high pass filter, 14...
AGC circuit, 15...Blank detection section, 16...
Dropout detection circuit, 17... Low pass filter, 18... Waveform shaping circuit, 19... First counter, 21... Frequency dividing circuit, 22... Pulse shaping circuit, 23... Pulse generation circuit, 24... Second Counter, 25... Count start/stop control circuit, 2
6...Exclusive OR circuit (EX OR circuit), 31...Sampling counter, 32,3
3...Counter.

Claims (1)

[Claims] 1. In a blank detection device for a magnetic recording/reproducing device using a rotating head, a dropout detection circuit detects a dropout of tape read information during high-speed playback, a counter that counts a dropout detection signal output from the dropout detection circuit, and the contents of this counter. A blank detection device comprising means for detecting a state in which the dropout detection signal is interrupted for a set time or more and outputting a blank detection signal.