DE4302748B4 - Method for playing a long game recording in a video recorder - Google Patents

Abstract

Method for reproducing a long-game recording in a video recorder at a tape speed which deviates from the nominal value, the magnetic tape being scanned using a plurality of heads, characterized in that a comparator signal is generated which indicates which of the heads in each case delivers the maximum signal amplitude, that of the Heads supplied useful signal is delayed by amounts dependent on the comparator signal and the amounts of the delay are dimensioned such that the lines of the useful signal assume their correct position within the prescribed line grid, and are dimensioned such that within the color signal the color synchronizing signal has a continuous phase alternation, and that the amount of delay is equal to a fraction of the line duration H, in particular 0 H, 0.25 H, 0.5 H, 0.75 H.

Description

The invention is based on one Playback procedure according to the generic term of claim 1.

At certain belt speeds, e.g. in LP (long play) there are tracking schemes that are used for trick play functions (Search, freeze frame, slow motion) Jump points in the line grid of the Let video signal arise. These irregularities in the sync pulse train cause failures in the monitor devices connected to the video recorder Horizontal sync. This is also called horizontal image shift (SKEW).

The necessary correction will be made known by a changeover switch and a delay line reached. The undelayed PB signal is sent to the switch inputs (Playback signal) and the PB signal delayed by a certain time is applied. through time information is switched between the two signals. The corrected output signal that will be fed to the monitor is tapped at the switch output. To trigger the switching operations mentioned above there are special detection circuits that use a line PLL Detect deviation from a continuous line grid. (Data sheet AN 3592, BA 7023).

In the search mode, the tracks from the video heads sampled. Because of the azimuth damping, each head can Read only every second track at a time. This results in the Scanning the FM packets of a double azimuth head at the inputs of the head amplifier applied signals. Depending on whether the LP head or the SP head on the accesses the respective track, there is a respective FM envelope. With a comparator signal the signal with the larger FM amplitude is then generated to the head amplifier connected through. At the head amplifier output becomes a continuous one FM signal generated without noise strips. This operating mode (Noiseless-Search) has so far only been implemented in the SP search.

The video tracks are in the LP search only scanned with a pair of heads (LP or SP heads). The result resulting FM has during the lane change strong level drops that turn out to be more or make less wide noise streaks noticeable on the screen (dependent the scan speed and the width of the video heads). conditioned due to the LP tracking scheme, the video signals have two successive ones FM packets have an offset of 0.5 H since only every other track is read can be.

For there is the restoration of the correct sync pulse sequence special detection circuits which use a line PLL to deviate from detect a continuous line grid. It will be a correction signal with a 0.5 H delay line for the SKEW correction is switched on or off. These special detection circuits also include a burst phase identifier / conditioning, a balance modulator and switching logic for the chrome correction. This detection circuit is not for the LP Noiseless Search mode use.

From the US 4,851,930 a method for playing back at a tape speed deviating from the nominal value in a video recorder is known, in which the magnetic tape is scanned with several heads. In this case, a comparator signal is generated, which supplies the phase offset of the heads, the useful signal supplied by the heads being delayed as a function of the comparator signal. From the DE 1 272 962 B a method for a video recorder is known in which a comparator signal is generated which indicates which of the heads delivers the maximum signal amplitude in each case. From the US 4,456,932 A playback method is known in which, in a special playback mode, the video signal is delayed by a fraction of the line duration H, for example 0 H, 0.25 H, 0.5 H, 0.75 H.

The invention is based on the object Procedure for a playback of LP recordings with changed tape speed without image and color disturbances to accomplish. This object is achieved by the specified in claim 1 Invention solved. Advantageous developments of the invention are specified in the subclaims.

The LP search results in an offset line grid and an irregular color signal sequence. The comparator signal, which from a head amplifier delivered, shows in a known manner which head of the the currently engaged head pair the larger FM supplies. Be in transition from one scanned track to another with this comparator signal the heads switched over, the comparator signal thus indicates that at the moment a tipping change takes place. Because the tracking scheme is known, the temporal offset of the now sampled signal in relation to to be known to that of the last track scanned. That is, through The switch is controlled by evaluating the comparator signal to compensate for the time error. The comparator signal becomes more suitable Processed further, the color signal is also corrected become.

The comparator signal controls one delay the line grid and the color signal sequence such that a continuous line grid results and a uniform alternating Color signal sequence is ensured.

The comparator signal thus becomes Correction of principle-related signal offsets when playing back LP recordings with modified Belt speed used. Furthermore control the comparator signal or control signals derived therefrom, a sequence of delays necessary for recovery of a continuous line grid. From the comparator signal derived pulse trains are used in conjunction with the delay train to control a color correction circuit for restoration the correct color signal sequence. A special sequence of delays, controlled by the comparator signal or control signals derived therefrom, serves for the simultaneous restoration of a continuous Line grid and correct color signal sequence, without additional effort for special Color signal processing.

The advantages of the invention lie in that none Decoder circuit for detecting a synchronous offset or one Error in the color sequence is necessary. The control logic is with Standard logic components or existing microprocessor very easy to implement. The effort for color correction can be omitted due to the special delay sequence described. On LP Noiseless Search is now feasible.

The invention is illustrated below the drawing explained. In it show:

1 Tracking scheme for SP and LP (known),

2 line screen correction according to the invention,

3 . 4 Delay circuits

5 an inventive tracking scheme for correct line grid and color signal sequence,

6 . 7 Color correction signal circuits

8th Waveforms

9 Corrected track position scheme with changed deceleration,

10 Waveforms of the delay correction circuit,

11 Tracking scheme with again changed delay times and

12 Delay waveforms.

1 shows the tracking schemes for the video recording types standard play SP and long play LP. While in SP the synchronizing pulses of adjacent tracks on the magnetic tape are always arranged next to each other, in LP they are offset from field to field by ¼ line. This offset has disadvantages, especially in trick modes such as search forward-reverse. In search mode, the changed tape speed scans several tracks per field.

With every transition from one track to the other others with LP there is an offset of the complete video signal by 0.25 H, which is a horizontal image offset on the connected TV noticeable. This line offset is activated by switching on delay lines balanced.

The head speed VH runs in the shown Direction. The belt speed VT runs in the direction shown with SP with 23.39 mm / s and with LP with 11.7 mm / s. The burst phases of ± 135 ° are different hatched.

2 represents the template scheme LP. The tracks a - i shown 2.1 are in 2.2 have been shifted by delays, so that the tracks a1 - i1 result. This results in a continuous line grid in the search run.

The delays for the individual lines are:
a to a1: 0 H (last scanned track before changing in the search)
b to b1: 0.25 H
c to c1: 0.5 H
d to d1: 0.75 H
e to e1: 0 H (from here the sequence repeats again)
f to f1: 0.25 H

The controlled delays result in a continuous line grid. The comparator signal is used to switch to the different delay lines. The comparator signal (H, L) indicates when the head is moving from one track to another, which head of the engaged double azimuth head pair delivers the higher FM level. When the head pair changes from one track to the adjacent track, the most suitable head is always switched on with this signal. The comparator signal therefore indicates whether the track is azimuth 2 CH2 or the track with azimuth 1 CH1 is read, or whether a transition has taken place. With this information, the above sequence of delays is switched.

3 shows a control of the individual delays, which is carried out with a digital circuit or a microprocessor. The signal profiles A and B drive the delay lines 0.25 H and 0.5 H in such a way that the corresponding delay sequence of 0 H, 0.25 H, 0.5 H, 0.75 H results, where H is the line duration , The PB signal is applied to the delay line 0.25 H and is then present at X1 of the switch S1. The PB signal is also present at switch S1 without delay. The output Z1 of the switch S1 is controlled by the signal course A. The signal W resulting at Z1 reaches the delay line 0.5 H on the one hand and then to the input X2 of the switch S2 and on the other hand to the input Y2 of the switch S2. The signal curve B then controls the switch S2 in such a way that the output signal StS (signal to scart) results at Z2.

4 makes another variant of the product development of the delay sequence. The PB signal reaches the input X1 of switch S1 without delay and via the delay stages 1 . 2 and 3 to inputs Y1, U1 and V1 of switch S1. The switch S1 continuously switches through the inputs X1, Y1, U1 and V1, so that the corresponding delay sequence results at the output Z1 of the switch S1, which is then output as a signal to Scart StS.

5 shows different tracking schemes 5a LP tracking schemes 5b a tracking scheme corrected by deceleration and 5c Tracking position scheme with a uniformly alternating color signal sequence corrected by a color correction signal FKS. According to 5b a correction for the color signal after the correction for luminance would only be unnecessary when moving from track d1 to e1 or h1 to i1. In order to obtain a correct color signal sequence for all track transitions, the color signal, controlled by a color correction signal FKS, is corrected. The color correction signal FKS controls a circuit 6 or 7 such that the alternation of the PAL burst phase (+ 135 °, -135 °) is maintained when changing lanes in the search from line to line.

6 shows a balanced modulator 4 , The Pb color signal COL is in the balanced modulator 4 mixed with the doubled ink carrier Fsc. After filtering out the lower sideband, the signal Col * is obtained. The switch S3 is controlled by the color correction signal FKS and switches the signal Col * or Col additively to the luminance L.

7 shows a 1 H delay line. The color signal Col is through the delay stage 6 delayed by one line and thus supplied to switch S3 as signal Col *. The switch S3 in turn switches the signal Col * or the signal Col additively to the luminance L depending on the activation of the color correction signal.

8th shows how the color correction signal FKS is obtained from the comparator signal via an auxiliary signal auxiliary. An auxiliary signal auxiliary, which is obtained from a counter, is used to switch between the comparator signal and the inverted comparator signal.

9 also shows a correction for luminance and color, but with the difference that a 1.25 H line is used instead of a 0.25 H delay line.

The delay for the individual lines is:
a to a3: 0 H (last scanned track until was changed in the search)
b to b3: 1.25 H
c to c3: 0.5 H
d to d3: 0.75 H
e to e3: 0 H (from here the sequence is repeated)
f to f3: 1.25 H

This shift results in 9b a continuous line grid. The color correction signal FKS 'adjusts a circuit 6 or 7 on. In addition to the continuous line grid, this also results in a uniform alternating color signal sequence when changing lanes in the search run.

10 shows the comparator signal Komp, the delay 0.75 H, the delay 0.5 H and the color correction signal FKS '. The delay then expires: 0 H; 1.25 H; 0.5 H; 0.75 H; 0 H; 1.25 H .... The simple generation of the color correction signal FKS 'and the signals for switching the delay with only one binary counter is advantageous.

11 shows the simultaneous correction of both components, luminance and color. So are the delay frequencies:
a to a5: 0 H (last scanned track before changing in the search)
b to b5: 1.25 H
c to c5: 0.5 H
d to d5: 1.75 H
e to e5: 1 H
f to f5: 0.25 H
g to g5: 1.5 H
h to h5: 0.75 H

The Pb signal is shifted from track to track so that color and luminance are corrected simultaneously. The great advantage here is that no effort is required for color signal processing. The sequences of the different delay times described so far apply only to LP operating modes "search forward" (reading the tracks in direction a to i). In the case of "reverse search" (reading the tracks in direction i to a), the delays must be switched on in reverse order. The pulse sequences of the color correction signal must also run from right to left. For 5 with the pulse trains 8th this results in the delay sequences: 0 H; 0.75 H; 0.5 H; 0.25 H; 0 H; 0.75 H ...

12 shows the corresponding pulse diagram. 12b shows the forward search with the comparator signal and the individual lines, the auxiliary signal and the color correction signal. 12a shows the search backwards with the comparator signal and the individual lines, the auxiliary signal and the color correction signal.

Claims (3)

Method for reproducing a long-game recording in a video recorder at a tape speed which deviates from the nominal value, the magnetic tape being scanned with a plurality of heads, characterized in that a comparator signal is generated which indicates which of the heads in each case delivers the maximum signal amplitude, that of the Heads delivered useful signal is delayed by amounts dependent on the comparator signal and the amounts of the delay so be are measured that the lines of the useful signal take their correct position within the prescribed line grid, and are dimensioned such that within the color signal the color synchronizing signal has a continuous phase alternation, and that the amount of delay is equal to a fraction of the line duration H, in particular 0 H , 0.25H, 0.5H, 0.75H. A method according to claim 1, characterized in that the comparator signal is based on the amplitude of a derived with the luminance signal frequency-modulated image carrier becomes. A method according to claim 1, characterized in that the amount of delay is dimensioned such that in each case by a specific value of the comparator signal a predetermined time sequence of delays with different amounts is triggered.