IE65895B1 - Video recorder with distortion corrector circuit - Google Patents

Abstract

In the signal path (1) for the frequency-modulated luminance signal of a video recorder, an equalising circuit (11) is disposed between the video band (2) and the frequency demodulator (3) which, whenever the luminance signals fall below a specific switching level (U16), operates in the mode of a bandpass filter (19) which is tuned to the carrier frequencies of the luminance signals and, whenever the luminance signals exceed this switching level in the direction of higher values, operates in the mode of an amplitude-controlled delay unit. In the latter mode, phase errors caused by recording and transmission are largely cancelled, whereas, in the former mode, oscillation patterns with deteriorated oscillations are again refreshed in terms of amplitude through the resonance effect. The height of switching level (U16) is set by a noise detection circuit (21) which detects the rate of the oscillations which do not pass through a specific detection level of the noise detection circuit situated in the vicinity of the sound point line of the frequency demodulator. The equalising circuit is thereby adapted to the different reproduction quality levels of different video tapes in such a way that image reproduction with minimum interference and maximum definition is achieved.

Description

Video recorder with distortion corrector circuit * * The present invention relates to a video recorder with an equalizing circuit in accordance with the precharacterizing part of Claim 1 or Claim 6.

From the German patent specification DE-3809394 there is known an equalizing circuit arranged in the signal path for processing the frequency-modulated luminance signals of a video recorder and containing a band-pass filter that is tuned to the deflection range of the part of the luminance signal that actually reproduces the luminance. This band-pass filter consists of a filter circuit component located in the signal path and a coupling component arranged downstream thereof, λ diode switch is also connected in parallel with the output of the filter circuit component. When the oscillation amplitudes of the frequency-modulated luminance signal at the output side of the filter circuit component exceed a switching voltage of the diode switch, the said voltage being defined in the vicinity of the flection point of the diode switch characteristic, ’ the diode switch will pass from a blocked state (off-state) to a conducting state (on-state) in this part of the characteristic and, together with the filter circuit component and the conducting state d.c. resistance of the diode switch, will form a transit-time controller with an amplitude-dependent delay of the transit time of the frequencymodulated luminance signal. In this control state of the equalizing circuit the transit time of the frequency-modulated luminance signals is therefore delayed in a manner proportional to the amplitude of their oscillations, so that these , sig1E. nals have their transit time corrected. This transit I □ time delay compensates frequency and phase frequency characteristic errors, especially in the lower-frequency range of the lower sideband of the carrier frequencies of the frequency-modulated luminance signal immediately adjacent to the range of variation of the carrier oscillations, so that the amplitude-modulated luminance signals at the 25 output side of the frequency modulator will maintain a linear frequency characteristic up to very high video frequencies (beyond 3 MHz), thereby making it possible to attain a very high image resolution in 30 the image reproduction from the videotape without any additional noise.

On the other hand, given small oscillation amplitudes of the transmitted frequency-modulated luminance signals that do not exceed the threshold value of the diode switch and therefore maintain the diode switch in its off-state, so that the entire distortion corrector circuit will be in the state of bandpass filter operation, the resonance effects of the band-pass filter, which to all intents and purposes trigger the basic or carrier oscillations of the frequency-modulated luminance signal, will make themselves felt.. This leads to the suppression,^ of Ί_ the low oscillations of the lower sideband of the frequency-modulated luminance signals, the said frequencies having superposed on them the carrier frequencies of the frequency-modulated luminance signals and being capable .- given adequate amplitudes in the vicinity of their maximum amplitude of taking the carrier frequencies of the frequencymodulated luminance signal out of the switching range of the frequency modulator. Furthermore, this will also increase the amplitude of the carrier oscillations themselves and reduce the noise signals in the frequency range above the carrier oscillations.

These measures ensure that a sharper image will be reproduced on the screen. Furthermore, the arrangement substantially eliminates the edge noises that' disturb image reproduction, especially the noises due to vertical luminance edges, as well as disturbing reflections and the defects described as '’flitter .

However, the practical application of these measures has shown that the quality of the recording of video * * information on the tape of a video cassette and the quality of the video tapes themselves are so widely divergent as to make it impossible to find a design or dimensioning of the known equalizing circuit that can cover in a satisfactory manner this wide range of differences in quality of the video'* cassettes to be reproduced.

Starting from this insight, the present invention is therefore underlain by the task of further develop20 ing a video recorder of the type just described and of doing so in such a manner that - over a very wide range of the disturbed oscillation or interference behaviour of the frequency-modulated luminance signal - the ?5 equalizing circuit will perform the amplitude-dependent compensation of the transit time and will further compensate the disturbed oscillations in such a way as to ensure image reproduction with the least possible disturbances while maintaining the greatest possible sharpness of the image. According to the present invention, this task is solved by the measures described in the characterizing part of Claim 1 or Claim 6.

The starting point of the solution is represented by the insight that disturbances will occur during the reproduction of video images above all when the amplitudes of the slow oscillations of the lower sideband of the frequency-modulated brightness signals arrive at the order of magnitude of the carrier oscillations of the frequency-modulated luminance signals. A substantial attenuation of these reproduction disturbances can therefore be obtained by reducing the ratio between the amplitudes of the low oscillations of the lower sideband and the amplitudes of the carrier oscillations of the frequencymodulated luminance signal. These measures of the present invention have the effect* of setting the starting level of a transmission circuit preceding the equalizing circuit or the switching level of the trigger via the ascertained average fault rate and an appropriate control signal formed therefrom and to do this in such a manner that the equalizing circuit will to all intents and purposes still be working as an amplitude-controlled transit-time delay circuit and ensure playback of the image with the best possible sharpness and the least possible disturbances due to flitter and edge noises.

As soon as image reproduction becomes subject to additional disturbances with an error rate that substantially exceeds the average error rate, the level of the frequency-modulated luminance signal on the input side of the equalizing circuit or the threshold voltage of the trigger is changed to such an extent that the equalizing circuit will be caused by these disturbed frequency-modulated luminance signals to pass predominantly into the control state of a band-pass filter circuit and - for the entire duration of this high disturbance rate - will work predominantly in the band-pass filter state and will therefore compensate the disturbed pattern of the oscillations of the frequency-modulated luminance signal in such a manner as to ensure that these oscillations will no longer produce any noticeable disturbances on the screen.

The setting of the level of the frequency-modulated luminance signal on the input side of the equalizing circuit, just like the setting of the switching level of the trigger Of the equalizing circuit, acts like a displacement into a range in which the equalizing circuit is always set for the reproduction of video images with optimal sharpness (definition). In this ’ way the image reproduction of a video recorder in accordance with the present invention is optimally matched to the quality of the video recording on a video tape, to the quality of the tape material itself, and the reproduction characteristics of the video recorder. The measures in accordance with the present invention therefore make it possible to reproduce video images on a screen with a considerable quality improvement as compared with the previous state of the art of image reproduction, i.e. relatively free of disturbances and with the best possible definition, and this even, when the quality,of the recording is poor and the reproduction channel employed is of poor transmission quality.

The dependent claims describe advantageous embodiments of the invention, which will be discussed in greater detail in the description hereinbelow. The appended drawings can be briefly described as follows: Figure 1 shows the block diagram of a signal path in accordance with the invention to be followed by the frequency-modulated luminance signals scanned from a recording support in a video recorder.

Figure 2 shows the diagrams a), b) and c) illustrating the production of the control signal to set an optimal quality of image reproduction, such signal being dependent on the rate of disturbed oscillations.

Figure 3 shows the diagrams of the frequency pattern of the frequency-modulated luminance signal on the input side of the equalizing circuit of the embodiment illustrated in Figure 1 for a recording and FM transmission of high, medium and low quality, Figure 4 shows diagrams (a) to (d3) of the sequence of oscillations of the frequency-modulated luminance signal on the input side of the equalizing circuit side of the trigger ,(.4a)' and on. the input (4b), of- the output signals of the disturbed oscillation or interference detector (4cl, 4c2, 4c3) and the rate of interference (4dl, 4d2, 4d3) in the case of high, medium and low transmission quality, Figure 5 shows- the block diagram of another embodiment of the signal path in accordance with the invention to be followed by the frequency-modulated luminance signals scanned from a recording support in a video recorder, and Figure 6 shows diagrams (a) to (c2) illustrating the 30 mode of. action of the interference detector contained . in the disturbance detection circuit of the embodiment shown in Figure 5 in the event of a particularly high local interference rate.

Figure 1 shows the block diagram of an Amhod j of the signal path 1 in a video recorder for the fre quency-raodulated luminance signals scanned from a video tape 2. This embodiment extends from the video tape 2 inserted in the video recorder right through to the frequency demodulator 3 included in the signal path l, the said frequency demodulator being used to convert the frequency-modulated luminance signal from an FM signal into an AM signal. The video signals recorded on the video tape 2 are scanned by the video head 4 of .the video recorder and then pass to the signal input 13 of the frequency demodulator 3 via a head amplifier 5, a separating filter circuit 6, a buffer amplifier 10, an equalizing circuit ii, and a further buffer amplifier 12. The separating filter circuit 6 serves to separate the frequency-modulated luminance signals from other signals scanned from the video tape 2. In the embodiment here illustrated the equalizing circuit 11 consists of an inductive filter circuit component 14, preceded by a capacitative coupling component 15, and a trigger ±6 connected to the signal path 1 at a point between the said filter circuit component 14 and the said coupling component 15, where the switching level U16 of the trigger 16 can be set by means of a control signal acting via the control input 27. The filter circuit component 14 and the coupling component 15 of the equalizing circuit 11 are designed and dimensioned in such a manner that - when the trigger 16 is in the nonconducting or first control state - these two circuit components will form a band-pass filter 19 with a bandwidth such as to transmit the range of variation of the carrier oscillation of the frequency-modulated video signal, the frequency of the said oscillation being the direct representation of the luminance of the image line to be transmitted. Furthermore, the filter circuit component 14 is so designed and so dimensioned that - when the trigger 16 is in the conducting or second control state - the filter circuit 14, together with the conducting-state resistance 25 of the trigger, will constitute an amplitude controlled monostable element 14/25 to control the transit time’ as a function of the amplitude. This transit time controller substantially compensates the phase errors that the frequency-modulated luminance signal has > suffered during the recording on the video tape 2 and the subsequent scanning therefrom.

An interference recognition circuit 21 is connected to the signal path 1 in the equalizing circuit 11 via another buffer amplifier 20. In the embodiment here illustrated this disturbance recogni- ..... tion circuit contains a missing-oscillation detector 22, a default rate circuit 23, and a current generator 24. The missing- oscillation detector 22 recognizes individual oscillations of the frequency-modulated luminance signal transmitted through the signal path 1 that are either missing or do not exceed a certain recognition threshold, producing an error signal F every time such a missing oscillation is detected. The default rate circuit 23 uses the rate of these error signals F to form an electric default rate signal 30 (Figure 2a) and this signal is then used by the current generator 24 to produce a control signal 31 (Figure 2b) for the control input 27 of the trigger ig that corresponds to the magnitude of the default rate signal 30.

Given the presence of the interference recognition circuit 21 and the adjustable value of the operating level U16 that it controls, it becomes possible to match the equalizing circuit 11 to the different recording qualities of the video tapes 2 and the transmission quality of the scanned signal up to the signal input 28 of the equalizing circuit in the signal path 1 for the frequencymodulated luminance signals. The diagram of Figure 3 shows the frequency response of the amplitudes A(FM) of the frequency-modulated ‘luminance signals plotted over the frequency axis f for three different recording qualities at the signal input 28 of the equalizing circuit 11, namely high quality (Curve 32), normal quality (Curve 33) and poor quality (Curve 34). This diagram indicates a range of variation 35 of the carrier oscillations 36 of the frequency-modulated luminance signal the frequency f(L) of these oscillations characterizing the actual luminance value of the transmitted signal. This range is followed on the lowfrequency side by the lower sideband 37, of which the oscillations 38 are responsible for the resolution and/or the sharpness of the reproduced' video image. In the embodiment here illustrated the frequency f(L) of the schematically represented carrier oscillation is 2.5 times greater than the frequency f(SB) of the sideband oscillation represented by the vertical distance 38 that is superposed on the carrier oscillation 36. The effect of this superposition is that the oscillation sequence of the carrier oscillation will from time to time go beyond the zero line area of the frequency-modulated luminance signals transmitted in signal path 1 and thus cause disturbances during the demodulation in the frequency demodulator 3 (as schematically illustrated in diagram a) of Figure 4). This diagram provides a schematic illustration of the oscillation sequences 38.1, 38.2 and 38.3 of the sideband oscillation 38 for a recording of high quality (38.1), a recording of normal quality (38.2) and a recordinq of poor quality (38.3) onto which there are superposed the carrier oscillations 36 of a recording of high quality, a recording of normal quality and a recording of poor quality, thus producing the oscillation sequences 39.1, 39.2 and 39.3 of a frequencymodulated luminance signal of a recording of high quality (39.1), normal quality (39.2) and poor quality (39.3) shown in diagram a). It can be seen from this diagram that the half-wave 39.22 of the oscillation sequence 39.2 of a normal recording quality and the'half-waves 39.32 and 39.35 of the oscillation sequence 39.3 of a poor recording quality do not overstep the zero line 26 of the frequency-modulated luminance signal. Also plotted in I diagram a) of Figure 4 are the lines 40.1, 40.2 and 40.3, which correspond to the operating values U16.1, U16.2 and U16.3 of the trigger that are set by the control signal 31 of the interference recognition circuit 21 at the control -. input 27 of the trigger χβ during the transmission of frequency-modulated luminance signals in a recording of high quality (Line 40.1), normal quality (Line 40.2) and poor quality (Line 40.3). Within the area round the zero line 26 that is delimited by the lines 40.1 or 40.2 or 40.3 the equalizing circuit 11 acts as a band-pass filter for the carrier oscillations 36 of the frequency-modulated luminance signals, while outside this area it behaves as an amplitude-controlled transit-time retarder whose delay time is determined by the part of the amplitude that lies beyond these delimitation lines 40.1, 40.2 and 40.3. In the embodiment here illustrated the switching process takes place with a switching pattern that corresponds to that of a switching diode at the flection point of its characteristic. Demodulation disturbances due to the switching process are therefore avoided.

Diagram b) of Figure 4 illustrates the oscillation sequences 45.1, 45.2 and 45.3 that the equalizing . circuit 11, acting under the influence of the set operating levels U16.1, U16.2 and Ό16.3, has formed at the signal input 29 of the trigger from the oscillation sequences 39.1 -to 39.3 of the frequency-modulated luminance signals in the signal path 1 illustrated in Figure 4a and which are evaluated by the i nterference recognition circuit 21. Given the inductive intermediate storage of the electric energy of the part of the half-waves that exceeds the operating level while the equalizing circuit operates as a transit-time retarder, the amplitude of the subsequent half-wave 39.22 will become considerably enlarged when the . equalizing circuit acts as a band-pass filter, so that in the embodiment here illustrated the half14 wave 45.22 of the oscillation sequence 45.2 in the signal path 1 at the signal input 29 of the trigger 16 will overstep the zero line 46 (Figure 4b), which is also- the switching-point line of the frequency demodulator 3. Consequently, all the half-waves of the oscillation sequences 39.1 to 39.3 illustrated in diagram a) of Figure 4, which have their counterpart in the oscillation sequences 45.1 to 45.3 in diagram b) of Figure 4, will be evaluated by the f requency modulator . 3. In diagram b) of Figure 4, there. are also shown - on -either side of the zero line (or switching-point line) 46 and lying close to it - the lines 47.1 and 47.2 which, form the a switching threshold for recognition thresholds Uel and Ue2 of the missing-oscillation detector 22 of the interference recognition circuit 21 referred to the signal path 1. As soon as one of the oscillations of the oscillation sequences 45.1 to 45.3 shown in diagram b) of Figure 4 exceeds one of the recognition thresholds 47.1 or 47.2, the discharge switch 41 (in the example here illustrated) will discharge the charging capacitor 42 of a charging component 43 of the missing oscillation detector 22. This discharge takes in a fraction of the length of a halfoscillation, so that the charging capacitor 42 can recharge before the attainment of a charging limit or the next discharge through the discharge switch 41. The charging circuit is dimensioned in such a manner as to ensure that the charging voltage U42 at the charging capacitor 42 will not exceed a charging threshold U44 of a charge detector 44 connected to 5 the said charging capacitor 42 within the greatest possible oscillation width TB of a half-wave of the carrier oscillations in the equalizing circuit 11. The charging threshold U44, in its turn, is so dimensioned .that the charging voltage U42 of the charging capacitor. 42 will be greater than the charging threshold U44 when the charging capacitor 42 is charged during the' smallest oscillation time of a .carrier oscillation 36. The curves . of the charging voltages U4 2 at the charging capacitor 42 are shown schematically in Figure 4 for a record20 ing of high quality (ci), a recording of normal quality (c2), and a recording of. poor quality (c3). These diagrams include a line 49 representing the charging threshold U44. Although the half-wave 45.22 for a normal-quality recording in diagram 4b does cross the switching-point line 46, this is no longer the case as regards the subsequent recognition threshold 47.2. Consequently, the charging . curve 48 in diagram 4c2 will cross the line 49 Of the charging threshold U44 at time t23, so that the charge detector 44 will at this time produce a default signal F for the default (disturbance) rate 35 circuit 23, as illustrated in diagram d2) of Figure for the scanning of a video tape with normal recording quality. During the schematically represented transmission of a recording of low quality (oscillation sequence 45.3) the half-wave 45.32 does not reach the appropriate recognition threshold 47.2 and the half-wave 45.35 of the same oscillation sequence 45.3 - after overstepping the switching-point line 46 - does not reach the re10 cognition threshold 47.1, so that the oscillation sequence 48 in diagram 4c3 will overstep the line 49 of the charging threshold U44 at both time-133 ' and time t36; the charging defector 44 - as illus15 trated in diagram d3) of Figure 4 for the reproduction of a poor-quality image of the video tape 2 - will therefore produce an error signal F at both moments of time.

As can be seen from diagrams dl) to d3) of Figure 4, of which diagram dl does not contain any default signals F, the density or rate of the default signals F increases as the recording quality diminishes, so that the default rate signal 30, which is formed by the defaul t rate circuit 23 and illustrated in diagram b) of Figure 2, represents a measure of the record30 ing quality and the transmission quality of the frequency-modulated luminance signals up to the signal input 28 of the equalizing circuit 11. The setting signal generator 24 preceding the default rate circuit 23 uses default rate signal 30 to form a control signal 31 for setting the operating level U16 of the trigger in such a way that - as far as possible - all the half-waves of the oscillation sequence of the frequency-modulated luminance signals passing through the equalizing circuit 11 will at least just cross the switching-point line 46. The inter-: ference recognition circuit 21 will therefore set a operating level ui6 at the trigger that will correspond to the average recording, quality of the image playback that is being transmitted at that instant and yield the best possible image definition with an image reproduction that is just free of disturbance. In the embodiment here illustrated, the operating level U16 of the of the trigger ie £s gradually lowered (from U16.1 to U16.3) as the recording quality diminishes (from curve 32 to curve 34 in the diagram of Figure 3).

Figure 5 shows another embodiment of the signal path for the frequency-modulated luminance signals scanned from a video support 2 in a video recorder according to the present invention. Identical circuit components and signals always bear the same reference number as in Figure 1. The embodiment illustrated by Figure 5 essentially differs from the embodiment of such a signal path shown in Figure 1 by virtue of the fact that the equalizing circuit is preceded by an adjustable transmission circuit in the fora of damping circuit 8 and, further, that the control signal 31 produced by the i nterference recognition circuit 21 is applied to the control input 27 of the damping circuit 8 and that the trigger 17 of this embodiment is made up of two antiparallel switching diodes 18, whence its operating level U17 is determined by the flection point of the characteristic of the two antiparallel switching diodes 18. In the embodiment here illustrated, the damping circuit 8 consists essentially of two derivation diodes 50 connected to the signal path 1 and a series resistance 51 arranged in the signal path upstream of the said derivation diodes i The series resistance 51, together with the volume resistances of the derivation diodes (which can be set by means of a d.c. setting voltage), constitutes a voltage divider for the frequency-modulated luminance signals arriving at the signal input 7 of the damping circuit 8. Damping of the frequency-modulated luminance signals in the embodiment according to Figure 5 has its counterpart in a raising of the operating level U16 from, for example, U16.3 to U16.1 in the embodiment according to Figure 1.

The thin unbroken line 52 in diagram a) of Figure represents an oscillation sequence of the frequency-modulated luminance signals at the control input 28 of the equalizing circuit 11 for normal recording quality of image reproduction. This recording quality has its counterpart in a rate of default signals p that is shown in diagram a) of Figure 2 to the left of the dividing line 53 and which produces a default rate signal 30 in the default rate circuit 23. This default rate signal, in its turn, produces a control current I in the current generator 24 of the interference recognition circuit 21 that will set the damping factor of the damping circuit 8 in such a manner that the mean value of the amplitudes of the normal half-oscillations 52.0 to 52.2 and 52.8 and 52.9 of the frequency-modulated luminance signals at the signal input 28 of the equalizing circuit 11 will constitute a certain ratio with the threshold level U17.0 applied to the said signal input 28. By means of the direct-current control voltage, this ratio is set in such a manner that the reproduced image will have the best possible definition and the least possible disturbances. A disturbance is indicated between the half-waves 52.2 and 52.8 of the oscillation sequence 52 of the frequency-modulated luminance signals. As is shown in diagrams bl) and cl) of Figure 6, this disturbance triggers additional default signals f in the interference recognition circuit 21. As these additional default signals accumulate, they will cause a considerable increase in the rate of the default signals this new condition being indicated in diagram a) of Figure 2 to the right of the dividing line 53. As can clearly be seen from diagram b) of Figure 2, this leads to a considerable step-up in the default rate signal 30. This temporary increase of the default rate signal 30 causes a change in the control current I produced by the · current generator 24, so that the damping factor of the damping circuit 8 will become greater. The oscillation sequence of the more strongly damped . luminance signal corresponding to the greater interference rate shown to the right of the dividing line 53 cf the diagrams in Figure 2 is represented in diagram a) of Figure 6 by the thick unbroken line 54. Given this damping of the original oscillation sequence 52 of the frequencymodulated luminance signals, proportionally greater parts of the oscillation sequence of the frequencymodulated luminance signals will now fall within the range in which the equalizing circuit operates as a band-pass filter, namely the parts of the oscillation sequence 54 that are projected between the lines 40.4 and 40.5 of the operating level U17 of the trigger 17 applied to the signal input 28 of the equalizing circuit ll. This measure ensures that the equalizing circuit 11 will tend to centre the oscillations of the disturbed parts of the oscillation sequence 54 more closely around the zero line 46 of the oscillation sequence 54 of the frequencymodulated luminance signals. The said zero line 46 is also the switching-point line of the frequency demodulator 3. In the disturbed zone, therefore, the disturbance signals on the screen will be considerably reduced and, at one and the same time, the image sharpness will be enhanced to the greatest possible extent. The disturbance zone thus regulated by the disturbed signal recognition circuit 21 produces an appropriately higher rate of default signals F that is added to the default rate corresponding to the recording quality as indicated in diagram a) of Figure 2 to the right of the dividing line 55; for as long as this higher default rate pertains, it will raise the value of the . defaultrate signal 30 shown schematically in diagrams b) and c) of Figure 2. This current signal shown in diagram c) of Figure 2, which will remain in being for as long as . the greater default rate prevails, will set the damping circuit 8 in such a manner that the oscillation sequence 54 of the frequency-modulated luminance signal will be applied to the signal input 28 of the equalizing circuit 11. The additional rate of default signals F (diagram c2 of Figure 6), which in the regulated state of the setting signal 31 (diagram c of Figure 2) characterizes the magnitude of the inter’'. ference of the disturbed part of the signal and whose production process is schematically illustrated by diagrams b) and c) of Figure 6, will maintain this setting until such time as the local interference causing the higher default rate has disappeared.

In the embodiment illustrated in Figure 5, moreover, an integrating level regulator 56 is connected to the signal path 1 upstream of the signal input 28 of the equalizing circuit 11. The level regulator 56 measures the average signal level in the signal path 1 upstream of the signal input 28 of the equalizing circuit 11 and, in the embodiment here illustrated, will set the control current through the derivation diodes 50 of the damping circuit 8, always provided that this proves necessary, in such a manner as to ensure that the average signal level upstream of the signal input 28 of the equalizing circuit 11 will not fall below a value below which the image reproduction quality would be substantially reduced on account of an excessively low signal level.

In a further embodiment, which will not be discussed in greater detail, the adjustable transmission ircuit 8 upstream of the signal input 28 of the equalizing circuit 11 takes the form of a symmetrical amplifier with a setting input that permits its amplification factor to be set, by means of an appropriate setting signal, to such value as may from time to time be required.

Claims (9)

1. Video Recorder - having an equalizing circuit (11) arranged in the signal path (1) for processing the frequency-modulated luminance signals, which equalizing circuit 10 - in a first control state forms a band-pass filter (19) adapted to the deviation range of the carriers of the frequency-modulated luminance signal portion representative of the luminance and - in a second control state forms an amplitude-controlled 15 monostable element (14/18) which progressively delays the phase of the frequency-modulated luminance signal as the signal amplitude increases, - and having a trigger (17) that switches over the equalizing circuit from a first to a second control state when the cycle 20 (52) of the frequency-modulated luminance signal passes a predetermined operating level (U17) in the equalizing circuit, characterised in that - the equalizing circuit (11) is preceded by a transmission circuit (8) that can be adjusted to a given output level via a control 25 input (27) - and that an interference recognition circuit (21) is connected to the signal path (1) for detecting missing individual oscillations of the frequency-modulated luminance signals transmitted in the equalizing circuit, or any such oscillations that do not pass a 30 given recognition level (Ue) of the interference recognition circuit, and for generating a control signal (31) representative of the rate (default rate signal (30)) of such individual oscillations for the control input (27) of the transmission circuit of a shape such that as the default rate of an 35 oscillation curve of the frequency-modulated luminance signal increases, the equalizing circuit is switched to the band-pass filter circuit state for an increasing portion of that oscillation curve. - 25

2. Video recorder according to claim 1, characterised in that the transmission circuit (8) is an attenuator circuit whose attenuation factors can be adjusted via a control input (27).

3. Video recorder according to claim 1, characterised in that the transmission circuit (8) is an adjustable amplifier with a control input whose amplification factor can be adjusted via that control input.

4. Video recorder according to claim 2, characterised in that the attenuator circuit (8) is a symmetrical voltage divider circuit comprising a series resistance (51) in the signal path (1) of the frequency-modulated luminance signals and two d.c.-controlled diode paths (50) arranged symmetrically therewith.

5. Video recorder according to any of claims 1 to 4 characterised in that there is connected between the signal path (1) and the transmission circuit (8) an intergrat.ing gain control (56) which additionally controls the output level of the transmission circuit in such a way that the average signal level of the frequencymodulated luminance signal (54) at the signal input (28) of the equalizing circuit (11) does not drop below a predetermined minimum level.

6. Video recorder - having an equalizing circuit (11) arranged in the signal path (1) for processing the frequency-modulated luminance signals, which equalizing circuit - in a first control state forms a band-pass filer (19) adapted to the deviation range of the carriers of the frequencymodulated luminance signal portion representative of the luminance and - 26 - in a second control state forms an amplitude-controlled monostable element (14/25) which progressively delays the phase of the frequency-modulated luminance signal as the signal amplitude increased, - and having a trigger (16) that switches over the equalizing circuit from a first to a second control state when the oscillation cycle (39) of the frequency-modulated luminance signal passes a predetermined operating level (U16) in the equalizing circuit, characterised in that - the operating level (U16) of the trigger (16) can be adjusted via a control input (27) - and that an interference recognition circuit (21) is connected to the signal path (1) for detecting missing individual oscillations (45.22, 45.32, 45.35) of the frequency-modulated luminance signals (45) transmitted in the equalizing circuit, or any such oscillations that do not pass a given recognition level (Ue) of the interference recognition circuity and for generating a control signal (31) representative of the rate (default rate signal (30)) of such individual oscillations for the control input (27) of the trigger (16) of a shape such that as the default rate of an oscillation curve of the frequencymodulated luminance signal increases, the equalising circuit is switched to the band-pass filter circuit state for an increasing portion of that oscillation curve.

7. Video recorder according to any of claims 1 to 6, characterised in that the interference recognition circuit (21) comprises the following functional groups: a missing-oscillation detector (22) for detecting in the frequency-modulated luminance signal (39,54), and indicating via a default signal (F), any missing individual oscillations or oscillations that do not pass a given recognition level (Ue) of the interference recognition circuit, a default rate circuit (23) for generating a default rate signal (30) from the default signal (F), and a current generator (24) connected downstream for generating a control signal (31) in response to the shape of the default rate signal. - z7

8. Video recorder according to any of claims 1 to 7 characterised in that the operating level of the trigger (16,17) is the mean value of a switching range formed in the manner of a diode switch changing over from the blocking range to the conducting range.

9. A video recorder, according to claim 1, substantially as described herein with reference to the accompanying drawings.